Part 5: FAA Aeronautical… | FAA Aeronautical…

AIM2/20/258/7/25 AIM

Section 5. Pilot/Controller Roles and Responsibilities

5−5−1. General

a. The roles and responsibilities of the pilot and controller for effective participation in the ATC system are

contained in several documents. Pilot responsibilities are in the CFRs and the air traffic controllers’ are in the

FAA Order JO 7110.65, Air Traffic Control, and supplemental FAA directives. Additional and supplemental

information for pilots can be found in the current Aeronautical Information Manual (AIM), Notices to Airmen,

Advisory Circulars and aeronautical charts. Since there are many other excellent publications produced by

nongovernment organizations, as well as other government organizations, with various updating cycles,

questions concerning the latest or most current material can be resolved by cross-checking with the above

mentioned documents.

b. The pilot−in−command of an aircraft is directly responsible for, and is the final authority as to the safe

operation of that aircraft. In an emergency requiring immediate action, the pilot−in−command may deviate from

any rule in the General Subpart A and Flight Rules Subpart B in accordance with 14 CFR section 91.3.

c. The air traffic controller is responsible to give first priority to the separation of aircraft and to the issuance

of radar safety alerts, second priority to other services that are required, but do not involve separation of aircraft

and third priority to additional services to the extent possible.

d. In order to maintain a safe and efficient air traffic system, it is necessary that each party fulfill their

responsibilities to the fullest.

e. The responsibilities of the pilot and the controller intentionally overlap in many areas providing a degree

of redundancy. Should one or the other fail in any manner, this overlapping responsibility is expected to

compensate, in many cases, for failures that may affect safety.

f. The following, while not intended to be all inclusive, is a brief listing of pilot and controller responsibilities

for some commonly used procedures or phases of flight. More detailed explanations are contained in other

portions of this publication, the appropriate CFRs, ACs and similar publications. The information provided is

an overview of the principles involved and is not meant as an interpretation of the rules nor is it intended to extend

or diminish responsibilities.

5−5−2. Air Traffic Clearance

a. Pilot.

1. Acknowledges receipt and understanding of an ATC clearance.

2. Reads back any hold short of runway instructions issued by ATC.

3. Requests clarification or amendment, as appropriate, any time a clearance is not fully understood or

considered unacceptable from a safety standpoint.

4. Promptly complies with an air traffic clearance upon receipt except as necessary to cope with an

emergency. Advises ATC as soon as possible and obtains an amended clearance, if deviation is necessary.

NOTE−

A clearance to land means that appropriate separation on the landing runway will be ensured. A landing clearance does

not relieve the pilot from compliance with any previously issued altitude crossing restriction.

b. Controller.

1. Issues appropriate clearances for the operation to be conducted, or being conducted, in accordance with

established criteria.

2. Assigns altitudes in IFR clearances that are at or above the minimum IFR altitudes in controlled airspace.

Pilot/Controller Roles and Responsibilities 5−5−1

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3. Ensures acknowledgement by the pilot for issued information, clearances, or instructions.

4. Ensures that readbacks by the pilot of altitude, heading, or other items are correct. If incorrect, distorted,

or incomplete, makes corrections as appropriate.

5−5−3. Contact Approach

a. Pilot.

1. Must request a contact approach and makes it in lieu of a standard or special instrument approach.

2. By requesting the contact approach, indicates that the flight is operating clear of clouds, has at least one

mile flight visibility, and reasonably expects to continue to the destination airport in those conditions.

3. Assumes responsibility for obstruction clearance while conducting a contact approach.

4. Advises ATC immediately if unable to continue the contact approach or if encounters less than 1 mile

flight visibility.

5. Is aware that if radar service is being received, it may be automatically terminated when told to contact

the tower.

REFERENCE−

Pilot/Controller Glossary Term− Radar Service Terminated.

b. Controller.

1. Issues clearance for a contact approach only when requested by the pilot. Does not solicit the use of this

procedure.

2. Before issuing the clearance, ascertains that reported ground visibility at destination airport is at least 1

mile.

3. Provides approved separation between the aircraft cleared for a contact approach and other IFR or special

VFR aircraft. When using vertical separation, does not assign a fixed altitude, but clears the aircraft at or below

an altitude which is at least 1,000 feet below any IFR traffic but not below Minimum Safe Altitudes prescribed

in 14 CFR section 91.119.

4. Issues alternative instructions if, in their judgment, weather conditions may make completion of the

approach impracticable.

5−5−4. Instrument Approach

a. Pilot.

1. Be aware that the controller issues clearance for approach based only on known traffic.

2. Follows the procedure as shown on the IAP, including all restrictive notations, such as:

(a) Procedure not authorized at night;

(b) Approach not authorized when local area altimeter not available;

(d) Procedure not authorized when glide slope not used;

(e) Straight-in minimums not authorized at night; etc.

(f) Radar required; or

(g) The circling minimums published on the instrument approach chart provide adequate obstruction

clearance and pilots should not descend below the circling altitude until the aircraft is in a position to make final

descent for landing. Sound judgment and knowledge of the pilot’s and the aircraft’s capabilities are the criteria

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for determining the exact maneuver in each instance since airport design and the aircraft position, altitude and

airspeed must all be considered.

REFERENCE−

AIM, Para 5−4−20, Approach and Landing Minimums.

3. Upon receipt of an approach clearance while on an unpublished route or being radar vectored:

(a) Complies with the minimum altitude for IFR; and

(b) Maintains the last assigned altitude until established on a segment of a published route or IAP, at

which time published altitudes apply.

4. There are currently two temperature limitations that may be published in the notes box of the middle

briefing strip on an instrument approach procedure (IAP). The two published temperature limitations are:

(a) A temperature range limitation associated with the use of baro−VNA V that may be published on a

United States PBN IAP titled RNA V (GPS) or RNA V (RNP); and/or

(b) A Cold Temperature Airport (CTA) limitation designated by a snowflake ICON and temperature in

Celsius (C) that is published on every IAP for the airfield.

5. Any planned altitude correction for the intermediate and/or missed approach holding segments must be

coordinated with ATC. Pilots do not have to advise ATC of a correction in the final segment.

REFERENCE−

AIM, Chapter 7, Section 3, Cold Temperature Barometric Altimeter Errors, Setting Procedures, and Cold Temperature Airports (CTA).

b. Controller.

1. Issues an approach clearance based on known traffic.

2. Issues an IFR approach clearance only after the aircraft is established on a segment of published route

or IAP, or assigns an appropriate altitude for the aircraft to maintain until so established.

5−5−5. Missed Approach

a. Pilot.

1. Executes a missed approach when one of the following conditions exist:

(a) Arrival at the Missed Approach Point (MAP) or the Decision Height (DH) and visual reference to the

runway environment is insufficient to complete the landing.

(b) Determines that a safe approach or landing is not possible (see subparagraph 5−4−21h).

2. Advises ATC that a missed approach will be made. Include the reason for the missed approach unless

the missed approach is initiated by ATC.

3. Complies with the missed approach instructions for the IAP being executed from the MAP, unless other

missed approach instructions are specified by ATC.

4. If executing a missed approach prior to reaching the MAP, fly the lateral navigation path of the instrument

procedure to the MAP. Climb to the altitude specified in the missed approach procedure, except when a maximum

altitude is specified between the final approach fix (FAF) and the MAP. In that case, comply with the maximum

altitude restriction. Note, this may require a continued descent on the final approach.

5. When applicable, apply cold temperature correction to missed approach segments. Advise ATC when

intending to apply cold temperature correction and of the amount of correction required for each affected

segment on initial contact (or as soon as possible). This information is required for ATC to provide aircraft

appropriate vertical separation between known traffic. The pilot must not apply an altitude correction to an

assigned altitude when provided an initial heading to fly or radar vector in lieu of published missed approach

procedures, unless approved by ATC.

Pilot/Controller Roles and Responsibilities 5−5−3

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REFERENCE−

AIM, Para 5−1−17, Cold Temperature Operations.

AIM, Chapter 7, Section 3, Cold Temperature Barometric Altimeter Errors, Setting Procedures, and Cold Temperature Airports (CTA).

6. Following a missed approach, requests clearance for specific action; i.e., another approach, hold for

improved conditions, proceed to an alternate airport, etc.

b. Controller.

1. Issues an approved alternate missed approach procedure if it is desired that the pilot execute a procedure

other than as depicted on the instrument approach chart.

2. May vector a radar identified aircraft executing a missed approach when operationally advantageous to

the pilot or the controller.

3. In response to the pilot’s stated intentions, issues a clearance to an alternate airport, to a holding fix, or

for reentry into the approach sequence, as traffic conditions permit.

5−5−6. Vectors

a. Pilot.

1. Promptly complies with headings and altitudes assigned to you by the controller.

2. Questions any assigned heading or altitude believed to be incorrect.

3. If operating VFR and compliance with any radar vector or altitude would cause a violation of any CFR,

advises ATC and obtains a revised clearance or instructions.

b. Controller.

1. Vectors aircraft in Class A, Class B, Class C, Class D, and Class E airspace:

(a) For separation.

(b) For noise abatement.

2. Vectors aircraft in Class A, Class B, Class C, Class D, Class E, and Class G airspace when requested by

the pilot.

3. Except where authorized for radar approaches, radar departures, special VFR, or when operating in

accordance with vectors below minimum altitude procedures, vector IFR aircraft at or above minimum vectoring

altitudes.

4. May vector aircraft off assigned procedures. When published altitude or speed restrictions are included,

controllers must assign an altitude, or if necessary, a speed.

5. May vector VFR aircraft, not at an A TC assigned altitude, at any altitude. In these cases, terrain separation

is the pilot’s responsibility.

5−5−7. Safety Alert

a. Pilot.

1. Initiates appropriate action if a safety alert is received from ATC.

2. Be aware that this service is not always available and that many factors affect the ability of the controller

to be aware of a situation in which unsafe proximity to terrain, obstructions, or another aircraft may be

developing.

b. Controller.

1. Issues a safety alert if aware an aircraft under their control is at an altitude which, in the controller’s

judgment, places the aircraft in unsafe proximity to terrain, obstructions or another aircraft. Types of safety alerts

are:

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(a) Terrain or Obstruction Alert. Immediately issued to an aircraft under their control if aware the

aircraft is at an altitude believed to place the aircraft in unsafe proximity to terrain or obstructions.

(b) Aircraft Conflict Alert. Immediately issued to an aircraft under their control if aware of an aircraft

not under their control at an altitude believed to place the aircraft in unsafe proximity to each other. With the alert,

they offer the pilot an alternative, if feasible.

2. Discontinue further alerts if informed by the pilot action is being taken to correct the situation or that the

other aircraft is in sight.

5−5−8. See and Avoid

a. Pilot. When meteorological conditions permit, regardless of type of flight plan or whether or not under

control of a radar facility, the pilot is responsible to see and avoid other traffic, terrain, or obstacles.

b. Controller.

1. Provides radar traffic information to radar identified aircraft operating outside positive control airspace

on a workload permitting basis.

2. Issues safety alerts to aircraft under their control if aware the aircraft is at an altitude believed to place

the aircraft in unsafe proximity to terrain, obstructions, or other aircraft.

5−5−9. Speed Adjustments

a. Pilot.

1. Advises A TC any time cruising airspeed varies plus or minus 5 percent or 10 knots, whichever is greater,

from that given in the flight plan.

2. Complies with speed adjustments from ATC unless:

(a) The minimum or maximum safe airspeed for any particular operation is greater or less than the

requested airspeed. In such cases, advises ATC.

NOTE−

It is the pilot’ s responsibility and prerogative to refuse speed adjustments considered excessive or contrary to the aircraft’ s

operating specifications.

(b) Operating at or above 10,000 feet MSL on an ATC assigned SPEED ADJUSTMENT of more than

250 knots IAS and subsequent clearance is received for descent below 10,000 feet MSL. In such cases, pilots

are expected to comply with 14 CFR section 91.117(a).

3. When complying with speed adjustment assignments, maintains an indicated airspeed within plus or

minus 10 knots or 0.02 Mach number of the specified speed.

b. Controller.

1. Assigns speed adjustments to aircraft when necessary but not as a substitute for good vectoring technique.

2. Adheres to the restrictions published in FAA Order JO 7110.65, Air Traffic Control, as to when speed

adjustment procedures may be applied.

3. Avoids speed adjustments requiring alternate decreases and increases.

4. Assigns speed adjustments to a specified IAS (KNOTS)/Mach number or to increase or decrease speed

using increments of 5 knots or multiples thereof.

5. Terminates ATC-assigned speed adjustments when no longer required by issuing further instructions to

pilots in the following manner:

(a) Advises pilots to “resume normal speed” when the aircraft is on a heading, random routing, charted

procedure, or route without published speed restrictions.

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(b) Instructs pilots to “comply with speed restrictions” when the aircraft is joining or resuming a charted

procedure or route with published speed restrictions.

CAUTION−

The phraseology “Climb via SID” requires compliance with all altitude and/or speed restrictions depicted on the

procedure.

procedure that contains published speed restrictions.

(d) Advises aircraft to “delete speed restrictions” when ATC assigned or published speed restrictions on

a charted procedure are no longer required.

(e) Clears pilots for approach without restating previously issued speed adjustments.

REFERENCE−

Pilot/Controller Glossary Term − Resume Normal Speed.

Pilot/Controller Glossary Term − Resume Published Speed.

6. Gives due consideration to aircraft capabilities to reduce speed while descending.

7. Does not assign speed adjustments to aircraft at or above FL 390 without pilot consent.

5−5−10. Traffic Advisories (Traffic Information)

a. Pilot.

1. Acknowledges receipt of traffic advisories.

2. Informs controller if traffic in sight.

3. Advises ATC if a vector to avoid traffic is desired.

4. Does not expect to receive radar traffic advisories on all traffic. Some aircraft may not appear on the radar

display. Be aware that the controller may be occupied with higher priority duties and unable to issue traffic

information for a variety of reasons.

5. Advises controller if service is not desired.

b. Controller.

1. Issues radar traffic to the maximum extent consistent with higher priority duties except in Class A

airspace.

2. Provides vectors to assist aircraft to avoid observed traffic when requested by the pilot.

3. Issues traffic information to aircraft in the Class B, Class C, and Class D surface areas for sequencing

purposes.

4. Controllers are required to issue traffic advisories to each aircraft operating on intersecting or

nonintersecting converging runways where projected flight paths will cross.

5−5−11. Visual Approach

a. Pilot.

1. If a visual approach is not desired, advises ATC.

2. Complies with controller’s instructions for vectors toward the airport of intended landing or to a visual

position behind a preceding aircraft.

3. The pilot must, at all times, have either the airport or the preceding aircraft in sight. After being cleared

for a visual approach, proceed to the airport in a normal manner or follow the preceding aircraft. Remain clear

of clouds while conducting a visual approach.

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4. If the pilot accepts a visual approach clearance to visually follow a preceding aircraft, you are required

to establish a safe landing interval behind the aircraft you were instructed to follow. You are responsible for wake

turbulence separation.

5. Advise A TC immediately if the pilot is unable to continue following the preceding aircraft, cannot remain

clear of clouds, needs to climb, or loses sight of the airport.

6. In the event of a go−around, the pilot is responsible to maintain terrain and obstruction avoidance until

reaching an ATC assigned altitude if issued.

7. Be aware that radar service is automatically terminated, without being advised by ATC, when the pilot

is instructed to change to advisory frequency.

8. Be aware that there may be other traffic in the traffic pattern and the landing sequence may differ from

the traffic sequence assigned by approach control or ARTCC.

b. Controller.

1. Do not clear an aircraft for a visual approach unless reported weather at the airport is ceiling at or above

1,000 feet and visibility is 3 miles or greater. When weather is not available for the destination airport, inform

the pilot and do not initiate a visual approach to that airport unless there is reasonable assurance that descent and

flight to the airport can be made visually.

2. Issue visual approach clearance when the pilot reports sighting either the airport or a preceding aircraft

which is to be followed.

3. Provide separation except when visual separation is being applied by the pilot.

4. Continue flight following and traffic information until the aircraft has landed or has been instructed to

change to advisory frequency.

5. For all aircraft, inform the pilot when the preceding aircraft is a heavy. Inform the pilot of a small aircraft

when the preceding aircraft is a B757. Visual separation is prohibited behind super aircraft.

6. When weather is available for the destination airport, do not initiate a vector for a visual approach unless

the reported ceiling at the airport is 500 feet or more above the MV A and visibility is 3 miles or more. If vectoring

weather minima are not available but weather at the airport is ceiling at or above 1,000 feet and visibility of 3

miles or greater, visual approaches may still be conducted.

5−5−12. Visual Separation

a. Pilot.

1. Acceptance of instructions to follow another aircraft or to provide visual separation from it is an

acknowledgment that the pilot will maneuver the aircraft as necessary to avoid the other aircraft or to maintain

in-trail separation. Pilots are responsible to maintain visual separation until flight paths (altitudes and/or courses)

diverge.

2. If instructed by ATC to follow another aircraft or to provide visual separation from it, promptly notify

the controller if you lose sight of that aircraft, are unable to maintain continued visual contact with it, or cannot

accept the responsibility for your own separation for any reason.

3. The pilot also accepts responsibility for wake turbulence separation under these conditions.

b. Controller. Applies visual separation only:

1. Within the terminal area when a controller has both aircraft in sight or by instructing a pilot who sees the

other aircraft to maintain visual separation from it.

2. Pilots are responsible to maintain visual separation until flight paths (altitudes and/or courses) diverge.

3. Within en route airspace when aircraft are on opposite courses and one pilot reports having seen the other

aircraft and that the aircraft have passed each other.

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5−5−13. VFR-on-top

a. Pilot.

1. This clearance must be requested by the pilot on an IFR flight plan, and if approved, allows the pilot the

choice (subject to any ATC restrictions) to select an altitude or flight level in lieu of an assigned altitude.

NOTE−

VFR−on−top is not permitted in certain airspace areas, such as Class A airspace, certain restricted areas, etc. Consequently,

IFR flights operating VFR−on−top will avoid such airspace.

REFERENCE−

AIM, Para 4−4−8, IFR Clearance VFR−on−top.

AIM, Para 4−4−11, IFR Separation Standards.

AIM, Para 5−3−2, Position Reporting.

AIM, Para 5−3−3, Additional Reports.

2. By requesting a VFR-on-top clearance, the pilot assumes the sole responsibility to be vigilant so as to

see and avoid other aircraft and to:

(a) Fly at the appropriate VFR altitude as prescribed in 14 CFR section 91.159.

(b) Comply with the VFR visibility and distance from clouds criteria in 14 CFR section 91.155, Basic

VFR Weather Minimums.

position reporting, radio communications, course to be flown, adherence to ATC clearance, etc.

3. Should advise ATC prior to any altitude change to ensure the exchange of accurate traffic information.

b. Controller.

1. May clear an aircraft to maintain VFR-on-top if the pilot of an aircraft on an IFR flight plan requests the

clearance.

2. Informs the pilot of an aircraft cleared to climb to VFR-on-top the reported height of the tops or that no

top report is available; issues an alternate clearance if necessary; and once the aircraft reports reaching

VFR-on-top, reclears the aircraft to maintain VFR-on-top.

3. Before issuing clearance, ascertain that the aircraft is not in or will not enter Class A airspace.

5−5−14. Instrument Departures

a. Pilot.

1. Prior to departure considers the type of terrain and other obstructions on or in the vicinity of the departure

airport.

2. Determines if obstruction avoidance can be maintained visually or that the departure procedure should

be followed.

3. Determines whether an obstacle departure procedure (ODP) and/or DP is available for obstruction

avoidance. One option may be a Visual Climb Over Airport (VCOA). Pilots must advise ATC as early as possible

of the intent to fly the VCOA prior to departure.

4. At airports where IAPs have not been published, hence no published departure procedure, determines

what action will be necessary and takes such action that will assure a safe departure.

b. Controller.

1. At locations with airport traffic control service, when necessary, specifies direction of takeoff, turn, or

initial heading to be flown after takeoff, consistent with published departure procedures (DP) or diverse vector

areas (DV A), where applicable.

2. At locations without airport traffic control service but within Class E surface area when necessary to

specify direction of takeoff, turn, or initial heading to be flown, obtains pilot’s concurrence that the procedure

will allow the pilot to comply with local traffic patterns, terrain, and obstruction avoidance.

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3. When the initial heading will take the aircraft off an assigned procedure (for example, an RNA V SID with

a published lateral path to a waypoint and crossing restrictions from the departure end of runway), the controller

will assign an altitude to maintain with the initial heading.

4. Includes established departure procedures as part of the ATC clearance when pilot compliance is

necessary to ensure separation.

5. At locations with both SIDs and DV As, ATC will provide an amended departure clearance to cancel a

previously assigned SID and subsequently utilize a DV A or vice versa. The amended clearance will be provided

to the pilot in a timely manner so that the pilot may confirm adequate climb performance exists to determine if

the amended clearance is acceptable, and brief the changes in advance of entering the runway.

6. At locations with a DV A, ATC is not permitted to utilize a SID and DV A concurrently.

5−5−15. Minimum Fuel Advisory

a. Pilot.

1. Advise A TC of your minimum fuel status when your fuel supply has reached a state where, upon reaching

destination, you cannot accept any undue delay.

2. Be aware this is not an emergency situation, but merely an advisory that indicates an emergency situation

is possible should any undue delay occur.

3. On initial contact the term “minimum fuel” should be used after stating call sign.

EXAMPLE−

Salt Lake Approach, United 621, “minimum fuel.”

4. Be aware a minimum fuel advisory does not imply a need for traffic priority.

5. If the remaining usable fuel supply suggests the need for traffic priority to ensure a safe landing, you

should declare an emergency due to low fuel and report fuel remaining in minutes.

REFERENCE−

Pilot/Controller Glossary Term− Fuel Remaining.

b. Controller.

1. When an aircraft declares a state of minimum fuel, relay this information to the facility to whom control

jurisdiction is transferred.

2. Be alert for any occurrence which might delay the aircraft.

5−5−16. RNAV and RNP Operations

a. Pilot.

1. If unable to comply with the requirements of an RNA V or RNP procedure, pilots must advise air traffic

control as soon as possible. For example, “N1234, failure of GPS system, unable RNA V , request amended

clearance.”

2. Pilots are not authorized to fly a published RNA V or RNP procedure (instrument approach, departure,

or arrival procedure) unless it is retrievable by the procedure name from the current aircraft navigation database

and conforms to the charted procedure. The system must be able to retrieve the procedure by name from the

aircraft navigation database, not just as a manually entered series of waypoints.

3. Whenever possible, RNA V routes (Q− or T−route) should be extracted from the database in their entirety,

rather than loading RNA V route waypoints from the database into the flight plan individually. However, selecting

and inserting individual, named fixes from the database is permitted, provided all fixes along the published route

to be flown are inserted.

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4. Pilots must not change any database waypoint type from a fly−by to fly−over, or vice versa. No other

modification of database waypoints or the creation of user−defined waypoints on published RNA V or RNP

procedures is permitted, except to:

(a) Change altitude and/or airspeed waypoint constraints to comply with an ATC clearance/instruction.

(b) Insert a waypoint along the published route to assist in complying with ATC instruction, example,

“Descend via the WILMS arrival except cross 30 north of BRUCE at/or below FL 210.” This is limited only to

systems that allow along−track waypoint construction.

5. Pilots of FMS−equipped aircraft, who are assigned an RNA V DP or STAR procedure and subsequently

receive a change of runway, transition or procedure, must verify that the appropriate changes are loaded and

available for navigation.

6. For RNA V 1 DPs and STARs, pilots must use a CDI, flight director and/or autopilot, in lateral navigation

mode. Other methods providing an equivalent level of performance may also be acceptable.

7. For RNA V 1 DPs and STARs, pilots of aircraft without GPS, using DME/DME/IRU, must ensure the

aircraft navigation system position is confirmed, within 1,000 feet, at the start point of take−off roll. The use of

an automatic or manual runway update is an acceptable means of compliance with this requirement. Other

methods providing an equivalent level of performance may also be acceptable.

8. For procedures or routes requiring the use of GPS, if the navigation system does not automatically alert

the flight crew of a loss of GPS, the operator must develop procedures to verify correct GPS operation.

9. RNA V terminal procedures (DP and STAR) may be amended by ATC issuing radar vectors and/or

clearances direct to a waypoint. Pilots should avoid premature manual deletion of waypoints from their active

“legs” page to allow for rejoining procedures.

10. RAIM Prediction: If TSO−C129 equipment is used to solely satisfy the RNA V and RNP requirement,

GPS RAIM availability must be confirmed for the intended route of flight (route and time). If RAIM is not

available, pilots need an approved alternate means of navigation.

REFERENCE−

AIM, Para 5−1−16, RNAV and RNP Operations.

11. Definition of “established” for RNA V and RNP operations. An aircraft is considered to be

established on-course during RNA V and RNP operations anytime it is within 1 times the required accuracy for

the segment being flown. For example, while operating on a Q-Route (RNA V 2), the aircraft is considered to be

established on-course when it is within 2 NM of the course centerline.

NOTE−

1. Pilots must be aware of how their navigation system operates, along with any AFM limitations, and confirm that the

aircraft’ s lateral deviation display (or map display if being used as an allowed alternate means) is suitable for the accuracy

of the segment being flown. Automatic scaling and alerting changes are appropriate for some operations. For example,

TSO-C129 systems change within 30 miles of destination and within 2 miles of F AF to support approach operations. For

some navigation systems and operations, manual selection of scaling will be necessary.

2. Pilots flying FMS equipped aircraft with barometric vertical navigation (Baro-VNAV) may descend when the aircraft is

established on-course following FMS leg transition to the next segment. Leg transition normally occurs at the turn bisector

for a fly-by waypoint (reference paragraph 1-2-1 for more on waypoints). When using full automation, pilots should monitor

the aircraft to ensure the aircraft is turning at appropriate lead times and descending once established on-course.

3. Pilots flying TSO-C129 navigation system equipped aircraft without full automation should use normal lead points to

begin the turn. Pilots may descend when established on-course on the next segment of the approach.

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Section 6. National Security and Interception Procedures

5−6−1. National Security

National security in the control of air traffic is governed by 14 Code of Federal Regulations (CFR) part 99,

Security Control of Air Traffic.

5−6−2. National Security Requirements

a. Pursuant to 14 CFR 99.7, Special Security Instructions, each person operating an aircraft in an Air Defense

Identification Zone (ADIZ) or Defense Area must, in addition to the applicable rules of part 99, comply with

special security instructions issued by the FAA Administrator in the interest of national security, pursuant to

agreement between the FAA and the Department of Defense (DoD), or between the FAA and a U.S. Federal

security or intelligence agency.

b. In addition to the requirements prescribed in this section, national security requirements for aircraft

operations to or from, within, or transiting U.S. territorial airspace are in effect pursuant to 14 CFR 99.7; 49

United States Code (USC) 40103, Sovereignty and Use of Airspace; and 49 USC 41703, Navigation of Foreign

Civil Aircraft. Aircraft operations to or from, within, or transiting U.S. territorial airspace must also comply with

all other applicable regulations published in 14 CFR.

c. Due to increased security measures in place at many areas and in accordance with 14 CFR 91.103, Preflight

Action, prior to departure, pilots must become familiar with all available information concerning that flight.

Pilots are responsible to comply with 14 CFR 91.137 ( Temporary flight restrictions in the vicinity of

disaster/hazard areas), 91.138 (Temporary flight restrictions in national disaster areas in the State of Hawaii),

91.141 (Flight restrictions in the proximity of the Presidential and other parties), and 91.143 (Flight limitation

in the proximity of space flight operations) when conducting flight in an area where a temporary flight restrictions

area is in effect, and should check appropriate NOTAMs during flight planning. In addition, NOTAMs may be

issued for National Security Areas (NSA) that temporarily prohibit flight operations under the provisions of 14

CFR 99.7.

REFERENCE−

AIM, Para 3−4−8, National Security Areas.

AIM, Para 3−5−3, Temporary Flight Restrictions.

d. Noncompliance with the national security requirements for aircraft operations contained in this section

may result in denial of flight entry into U.S. territorial airspace or ground stop of the flight at a U.S. airport.

e. Pilots of aircraft that do not adhere to the procedures in the national security requirements for aircraft

operations contained in this section may be intercepted, and/or detained and interviewed by federal, state, or local

law enforcement or other government personnel.

5−6−3. Definitions

a. Air Defense Identification Zone (ADIZ) means an area of airspace over land or water, in which the ready

identification, location, and control of all aircraft (except Department of Defense and law enforcement aircraft)

is required in the interest of national security.

b. Defense Area means any airspace of the contiguous U.S. that is not an ADIZ in which the control of aircraft

is required for reasons of national security.

c. U.S. territorial airspace, for the purposes of this section, means the airspace over the U.S., its territories,

and possessions, and the airspace over the territorial sea of the U.S., which extends 12 nautical miles from the

baselines of the U.S., determined in accordance with international law.

d. To U.S. territorial airspace means any flight that enters U.S. territorial airspace after departure from a

location outside of the U.S., its territories or possessions, for landing at a destination in the U.S., its territories

or possessions.

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e. From U.S. territorial airspace means any flight that exits U.S. territorial airspace after departure from a

location in the U.S., its territories or possessions, and lands at a destination outside the U.S., its territories or

possessions.

f. Within U.S. territorial airspace means any flight departing from a location inside of the U.S., its territories

or possessions, which operates en route to a location inside the U.S., its territories or possessions.

g. Transit or transiting U.S. territorial airspace means any flight departing from a location outside of the U.S.,

its territories or possessions, which operates in U.S. territorial airspace en route to a location outside the U.S.,

its territories or possessions without landing at a destination in the U.S., its territories or possessions.

h. Aeronautical facility, for the purposes of this section, means a communications facility where flight plans

or position reports are normally filed during flight operations.

5−6−4. ADIZ Requirements

a. To facilitate early identification of all aircraft in the vicinity of U.S. airspace boundaries, Air Defense

Identification Zones (ADIZ) have been established. All aircraft must meet certain requirements to facilitate early

identification when operating into, within, and across an ADIZ, as described in 14 CFR 99.

b. Requirements for aircraft operations are as follows:

1. Transponder Requirements. Unless otherwise authorized by ATC, each aircraft conducting operations

into, within, or across the contiguous U.S. ADIZ must be equipped with an operable radar beacon transponder.

The transponder must be turned on and squawking a discrete beacon code assigned by ATC or issued by FSS

and displaying the aircraft altitude. Use of beacon code 1200 is not authorized. Use of the Universal Access

Transceiver (UAT) anonymity mode is not authorized.

(a) For air defense purposes, aircraft equipped with an operable 1090es (DO−260b) ADS−B system

operating outbound across the contiguous U.S. ADIZ may also be identified by the ICAO aircraft address

(otherwise known as the aircraft Mode S code). Therefore, use of a privacy ICAO aircraft address by outbound

aircraft is not authorized.

(b) Pilots of outbound VFR aircraft must squawk a discrete beacon code assigned by ATC or issued by

FSS.

REFERENCE−

14 CFR 99.13, Transponder−On Requirements.

14 CFR 91.225, Automatic Dependent Surveillance−Broadcast (ADS−B) Out equipment and use.

2. Two−way Radio. In accordance with 14 CFR 99.9, Radio Requirements , any person operating in an

ADIZ must maintain two−way radio communication with an appropriate aeronautical facility. For two −way

radio communications failure, follow instructions contained in 14 CFR 99.9.

3. Flight Plan. In accordance with 14 CFR 99.11, Flight Plan Requirements, and 14 CFR 99.9, except as

specified in subparagraph 5−6−4e, no person may operate an aircraft into, within, or from a departure point within

an ADIZ, unless the person files, activates, and closes a flight plan with an appropriate aeronautical facility, or

is otherwise authorized by air traffic control as follows:

(a) Pilots must file an Instrument Flight Rules (IFR) flight plan or file a Defense Visual Flight Rules

(DVFR) flight plan containing the time and point of ADIZ penetration;

(b) The pilot must activate the DVFR flight plan with U.S. Flight Service and set the aircraft transponder

to the assigned discrete beacon code prior to entering the ADIZ;

in the flight plan, except for (d) below;

(d) If the airport of departure within the Alaskan ADIZ has no facility for filing a flight plan, the flight

plan must be filed immediately after takeoff or when within range of an appropriate aeronautical facility;

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(e) State aircraft (U.S. or foreign) planning to operate through an ADIZ should enter ICAO Code M in

Item 8 of the flight plan to assist in identification of the aircraft as a state aircraft.

c. Position Reporting Before Penetration of ADIZ.

In accordance with 14 CFR 99.15, Position Reports, before entering the ADIZ, the pilot must report to an

appropriate aeronautical facility as follows:

1. IFR flights in controlled airspace. The pilot must maintain a continuous watch on the appropriate

frequency and report the time and altitude of passing each designated reporting point or those reporting points

specified or requested by ATC, except that while the aircraft is under radar control, only the passing of those

reporting points specifically requested by ATC need be reported. (See 14 CFR 91.183(a), IFR Communications.)

2. DVFR flights and IFR flights in uncontrolled airspace:

(a) The time, position, and altitude at which the aircraft passed the last reporting point before penetration

and the estimated time of arrival over the next appropriate reporting point along the flight route;

(b) If there is no appropriate reporting point along the flight route, the pilot reports at least 15 minutes

before penetration: the estimated time, position, and altitude at which the pilot will penetrate; or

from complying with (a) or (b) above, the pilot must report immediately after departure: the time of departure,

the altitude, and the estimated time of arrival over the first reporting point along the flight route.

3. Foreign civil aircraft. If the pilot of a foreign civil aircraft that intends to enter the U.S. through an ADIZ

cannot comply with the reporting requirements in subparagraphs c1 or c2 above, as applicable, the pilot must

report the position of the aircraft to the appropriate aeronautical facility not less than 1 hour and not more than

2 hours average direct cruising distance from the U.S.

d. Land−Based ADIZ. Land−Based ADIZ are activated and deactivated over U.S. metropolitan areas as

needed, with dimensions, activation dates and other relevant information disseminated via NOTAM. Pilots

unable to comply with all NOTAM requirements must remain clear of Land −Based ADIZ. Pilots entering a

Land−Based ADIZ without authorization or who fail to follow all requirements risk interception by military

fighter aircraft.

e. Exceptions to ADIZ requirements.

1. Except for the national security requirements in paragraph 5−6−2, transponder requirements in

subparagraph 5−6−4b1, and position reporting in subparagraph 5−6−4c, the ADIZ requirements in 14 CFR part

99 described in this section do not apply to the following aircraft operations pursuant to section 99.1(b),

Applicability:

(a) Within the 48 contiguous States or within the State of Alaska, on a flight which remains within 10

NM of the point of departure;

(b) Operating at true airspeed of less than 180 knots in the Hawaii ADIZ or over any island, or within

12 NM of the coastline of any island, in the Hawaii ADIZ;

continuous listening watch on the appropriate frequency; or

(d) Operating at true airspeed of less than 180 knots in the Guam ADIZ.

2. An FAA air route traffic control center (ARTCC) may exempt certain aircraft operations on a local basis

in concurrence with the DoD or pursuant to an agreement with a U.S. Federal security or intelligence agency.

(See 14 CFR 99.1 for additional information.)

f. A VFR flight plan filed inflight makes an aircraft subject to interception for positive identification when

entering an ADIZ. Pilots are therefore urged to file the required DVFR flight plan either in person or by telephone

prior to departure when able.

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5−6−5. Civil Aircraft Operations To or From U.S. Territorial Airspace

a. Civil aircraft, except as described in subparagraph 5−6−5b below, are authorized to operate to or from U.S.

territorial airspace if in compliance with all of the following conditions:

1. File and are on an active flight plan (IFR, VFR, or DVFR);

2. Are equipped with an operational transponder with altitude reporting capability, and continuously

squawk an ATC assigned transponder code;

3. Maintain two−way radio communications with ATC;

4. Comply with all other applicable ADIZ requirements described in paragraph 5 −6−4 and any other

national security requirements in paragraph 5−6−2;

5. Comply with all applicable U.S. Customs and Border Protection (CBP) requirements, including Advance

Passenger Information System (APIS) requirements (see subparagraph 5−6−5c below for CBP APIS

information), in accordance with 19 CFR part 122, Air Commerce Regulations; and

6. Are in receipt of, and are operating in accordance with, an FAA routing authorization if the aircraft is

registered in a U.S. State Department−designated special interest country or is operating with the ICAO three

letter designator (3LD) of a company in a country listed as a U.S. State Department−designated special interest

country, unless the operator holds valid FAA part 129 operations specifications. VFR and DVFR flight

operations are prohibited for any aircraft requiring an FAA routing authorization. (See paragraph 5 −6−11 for

FAA routing authorization information).

b. Civil aircraft registered in the U.S., Canada, or Mexico with a maximum certificated takeoff gross weight

of 100,309 pounds (45,500 kgs) or less that are operating without an operational transponder, and/or the ability

to maintain two−way radio communications with ATC, are authorized to operate to or from U.S. territorial

airspace over Alaska if in compliance with all of the following conditions:

1. Depart and land at an airport within the U.S. or Canada;

2. Enter or exit U.S. territorial airspace over Alaska north of the fifty−fourth parallel;

3. File and are on an active flight plan;

4. Comply with all other applicable ADIZ requirements described in paragraph 5 −6−4 and any other

national security requirements in paragraph 5−6−2;

5. Squawk 1200 if VFR and equipped with a transponder; and

6. Comply with all applicable U.S. CBP requirements, including Advance Passenger Information System

(APIS) requirements (see subparagraph 5−6−5c below for CBP APIS information), in accordance with 19 CFR

part 122, Air Commerce Regulations.

c. CBP APIS Information. Information about U.S. CBP APIS requirements is available at

http://www.cbp.gov.

5−6−6. Civil Aircraft Operations Within U.S. Territorial Airspace

a. Civil aircraft with a maximum certificated takeoff gross weight less than or equal to 100,309 pounds

(45,500 kgs) are authorized to operate within U.S. te rritorial airspace in accordance with all applicable

regulations and VFR in airport traffic pattern areas of U.S. airports near the U.S. border, except for those

described in subparagraph 5−6−6b below.

b. Civil aircraft with a maximum certificated takeoff gross weight less than or equal to 100,309 pounds

(45,500 kgs) and registered in a U.S. State Department−designated special interest country or operating with the

ICAO 3LD of a company in a country listed as a U.S. State Department −designated special interest country,

unless the operator holds valid FAA part 129 operations specifications, must operate within U.S. territorial

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airspace in accordance with the same requirements as civil aircraft with a maximum certificated takeoff gross

weight greater than 100,309 pounds (45,500 kgs), as described in subparagraph 5−6−6c below.

c. Civil aircraft with a maximum certificated takeoff gross weight greater than 100,309 pounds (45,500 kgs)

are authorized to operate within U.S. territorial airspace if in compliance with all of the following conditions:

1. File and are on an active flight plan (IFR or VFR);

2. Equipped with an operational transponder with altitude reporting capability, and continuously squawk

an ATC assigned transponder code;

3. Equipped with an operational ADS−B Out when operating in airspace specified in 14 CFR 91.225;

4. Maintain two−way radio communications with ATC;

5. Aircraft not registered in the U.S. must operate under an approved Transportation Security

Administration (TSA) aviation security program (see paragraph 5 −6−10 for TSA aviation security program

information) or in accordance with an FAA/TSA airspace waiver (see paragraph 5−6−9 for FAA/TSA airspace

waiver information), except as authorized in 5−6−6c7. below;

6. Are in receipt of, and are operating in accordance with an FAA routing authorization and an FAA/TSA

airspace waiver if the aircraft is registered in a U.S. State Department−designated special interest country or is

operating with the ICAO 3LD of a company in a country listed as a U.S. State Department−designated special

interest country, unless the operator holds valid FAA part 129 operations specifications. VFR and DVFR flight

operations are prohibited for any aircraft requiring an FAA routing authorization. (See paragraph 5 −6−11 for

FAA routing authorization information.); and

7. Aircraft not registered in the U.S., when conducting post −maintenance, manufacturer, production, or

acceptance flight test operations, are exempt from the requirements in 5 −6−6c5 above if all of the following

requirements are met:

(a) A U.S. company must have operational control of the aircraft;

(b) An FAA−certificated pilot must serve as pilot in command;

(d) “Maintenance Flight” is included in the remarks section of the flight plan.

5−6−7. Civil Aircraft Operations Transiting U.S. Territorial Airspace

a. Civil aircraft (except those operating in accordance with subparagraphs 5 −6−7b, 5−6−7c, 5−6−7d, and

5−6−7e) are authorized to transit U.S. territorial airspace if in compliance with all of the following conditions:

1. File and are on an active flight plan (IFR, VFR, or DVFR);

2. Equipped with an operational transponder with altitude reporting capability and continuously squawk

an ATC assigned transponder code;

3. Equipped with an operational ADS−B Out when operating in airspace specified in 14 CFR 91.225;

4. Maintain two−way radio communications with ATC;

5. Comply with all other applicable ADIZ requirements described in paragraph 5 −6−4 and any other

national security requirements in paragraph 5−6−2;

6. Are operating under an approved TSA aviation security program (see paragraph 5−6−10 for TSA aviation

security program information) or are operating with and in accordance with an FAA/TSA airspace waiver (see

paragraph 5−6−9 for FAA/TSA airspace waiver information), if:

(a) The aircraft is not registered in the U.S.; or

(b) The aircraft is registered in the U.S. and its maximum takeoff gross weight is greater than 100,309

pounds (45,500 kgs);

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7. Are in receipt of, and are operating in accordance with, an FAA routing authorization if the aircraft is

registered in a U.S. State Department−designated special interest country or is operating with the ICAO 3LD of

a company in a country listed as a U.S. State Department−designated special interest country, unless the operator

holds valid FAA part 129 operations specifications. VFR and DVFR flight operations are prohibited for any

aircraft requiring an FAA routing authorization. (See paragraph 5−6−11 for FAA routing authorization

information.)

b. Civil aircraft registered in Canada or Mexico, and engaged in operations for the purposes of air ambulance,

firefighting, law enforcement, search and rescue, or emergency evacuation are authorized to transit U.S.

territorial airspace within 50 NM of their respective borders with the U.S., with or without an active flight plan,

provided they have received and continuously transmit an ATC−assigned transponder code.

c. Civil aircraft registered in Canada, Mexico, Bahamas, Bermuda, Cayman Islands, or the British Virgin

Islands with a maximum certificated takeoff gross weight of 100,309 pounds (45,500 kgs) or less are authorized

to transit U.S. territorial airspace if in compliance with all of the following conditions:

1. File and are on an active flight plan (IFR, VFR, or DVFR) that enters U.S. territorial airspace directly

from any of the countries listed in this subparagraph 5−6−7c. Flights that include a stop in a non−listed country

prior to entering U.S. territorial airspace must comply with the requirements prescribed by subparagraph 5−6−7a

above, including operating under an approved TSA aviation security program (see paragraph 5−6−10 for TSA

aviation program information) or operating with, and in accordance with, an FAA/TSA airspace waiver (see

paragraph 5−6−9 for FAA/TSA airspace waiver information).

2. Equipped with an operational transponder with altitude reporting capability and continuously squawk

an ATC assigned transponder code;

3. Equipped with an operational ADS−B Out when operating in airspace specified in 14 CFR 91.225;

4. Maintain two−way radio communications with ATC; and

5. Comply with all other applicable ADIZ requirements described in paragraph 5 −6−4 and any other

national security requirements in paragraph 5−6−2.

d. Civil aircraft registered in Canada, Mexico, Bahamas, Bermuda, Cayman Islands, or the British Virgin

Islands with a maximum certificated takeoff gross weight greater than 100,309 pounds (45,500 kgs) must

comply with the requirements subparagraph 5 −6−7a, including operating under an approved TSA aviation

security program (see paragraph 5 −6−10 for TSA aviation program information) or operating with, and in

accordance with, an FAA/TSA airspace waiver (see paragraph 5−6−9 for FAA/TSA airspace waiver

information).

e. Civil aircraft registered in the U.S., Canada, or Mexico with a maximum certificated takeoff gross weight

of 100,309 pounds (45,500 kgs) or less that are operating without an operational transponder and/or the ability

to maintain two−way radio communications with ATC, are authorized to transit U.S. territorial airspace over

Alaska if in compliance with all of the following conditions:

1. Enter and exit U.S. territorial airspace over Alaska north of the fifty−fourth parallel;

2. File and are on an active flight plan;

3. Squawk 1200 if VFR and equipped with a transponder.

4. Comply with all other applicable ADIZ requirements described in paragraph 5 −6−4 and any other

national security requirements in paragraph 5−6−2.

5−6−8. Foreign State Aircraft Operations

a. Foreign state aircraft are authorized to operate in U.S. territorial airspace if in compliance with all of the

following conditions:

1. File and are on an active IFR flight plan;

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2. Equipped with an operational transponder with altitude reporting capability and continuously squawk

an ATC assigned transponder code;

3. Equipped with an operational ADS−B Out when operating in airspace specified in 14 CFR 91.225;

4. Maintain two−way radio communications with ATC; and

5. Comply with all other applicable ADIZ requirements described in paragraph 5 −6−4 and any other

national security requirements in paragraph 5−6−2.

b. Diplomatic Clearances. Foreign state aircraft may operate to or from, within, or in transit of U.S. territorial

airspace only when authorized by the U.S. State Department by means of a diplomatic clearance, except as

described in subparagraph 5−6−8i below.

1. Information about diplomatic clearances is available at the U.S. State Department website

https://www.state.gov/diplomatic−aircraft−clearance−procedures−for−foreign−state−aircraft−to−operate−in−

united−states−national−airspace/ (lower case only).

2. A diplomatic clearance may be initiated by contacting the U.S. State Department via email at

[email protected] or via phone at (202) 453−8390.

NOTE−

A diplomatic clearance is not required for foreign state aircraft operations that transit U.S. controlled oceanic airspace but

do not enter U.S. territorial airspace. (See subparagraph 5−6−8d for flight plan information.)

c. An FAA routing authorization for state aircraft operations of special interest countries listed in

subparagraph 5−6−11b. is required before the U.S. State Department will issue a diplomatic clearance for such

operations. (See subparagraph 5−6−11 for FAA routing authorizations information).

d. Foreign state aircraft operating with a diplomatic clearance must navigate U.S. territorial airspace on an

active IFR flight plan, unless specifically approved for VFR flight operations by the U.S. State Department in

the diplomatic clearance.

NOTE−

Foreign state aircraft operations to or from, within, or transiting U.S. territorial airspace; or transiting any U.S. controlled

oceanic airspace, should enter ICAO code M in Item 8 of the flight plan to assist in identification of the aircraft as a state

aircraft.

e. A foreign aircraft that operates to or from, within, or in transit of U.S. territorial airspace while conducting

a state aircraft operation is not authorized to change its status as a state aircraft during any portion of the approved,

diplomatically cleared itinerary.

f. A foreign aircraft described in subparagraph 5 −6−8e above may operate from or within U.S. territorial

airspace as a civil aircraft operation, once it has completed its approved, diplomatically cleared itinerary, if the

aircraft operator is:

1. A foreign air carrier that holds valid FAA part 129 operations specifications; and

2. Is in compliance with all other requirements applied to foreign civil aircraft operations from or within

U.S. territorial airspace. (See paragraphs 5−6−5 and 5−6−6.)

g. Foreign state aircraft operations are not authorized to or from Ronald Reagan Washington National Airport

(KDCA).

h. Foreign state aircraft operating with a U.S. Department of State issued Diplomatic Clearance Number in

the performance of official missions are author ized to deviate from the Automatic Dependent

Surveillance−Broadcast (ADS−B) Out requirements contained in 14 CFR §§ 91.225 and 91.227. All foreign state

aircraft and/or operators associated with Department of Defense missions should contact their respective offices

for further information on handling. Foreign state aircraft not associated with Department of Defense should

coordinate with U.S. Department of State through the normal diplomatic clearance process.

i. Diplomatic Clearance Exceptions. State aircraft operations on behalf of the governments of Canada and

Mexico conducted for the purposes of air ambulance, firefighting, law enforcement, search and rescue, or

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emergency evacuation are authorized to transit U.S. territorial airspace within 50 NM of their respective borders

with the U.S., with or without an active flight plan, provided they have received and continuously transmit an

ATC assigned transponder code. State aircraft operations on behalf of the governments of Canada and Mexico

conducted under this subparagraph 5−6−8h are not required to obtain a diplomatic clearance from the U.S. State

Department.

5−6−9. FAA/TSA Airspace Waivers

a. Operators may submit requests for FAA/TSA airspace waivers at https://waivers.faa.gov by selecting

“international” as the waiver type.

b. Information regarding FAA/TSA airspace waivers can be found at:

http://www.tsa.gov/for−industry/general−aviation or can be obtained by contacting TSA at (571) 227−2071.

c. All existing FAA/TSA waivers issued under previous FDC NOTAMS remain valid until the expiration date

specified in the waiver, unless sooner superseded or rescinded.

5−6−10. TSA Aviation Security Programs

a. Applicants for U.S. air operator certificates will be provided contact information for TSA aviation security

programs by the U.S. Department of Transportation during the certification process.

b. For information about applicable TSA security programs:

1. U.S. air carriers and commercial operators must contact their TSA Principal Security Specialist (PSS);

and

2. Foreign air carriers must contact their International Industry Representative (IIR).

5−6−11. FAA Flight Routing Authorizations

a. Information about FAA routing authorizations for U.S. State Department −designated special interest

country flight operations to or from, within, or transiting U.S. territorial airspace is available by country at:

1. FAA website http://www.faa.gov/air_traffic/publications/us_restrictions/; or

2. Phone by contacting the FAA System Operations Support Center (SOSC) at (202) 267−8115.

b. Special Interest Countries. The U.S. State Department−designated special interest countries are Cuba, Iran,

The Democratic People’s Republic of Korea (North Korea), The People’s Republic of China, The Russian

Federation, Sudan, and Syria.

NOTE−

F AA flight routing authorizations are not required for aircraft registered in Hong Kong, Taiwan, or Macau.

c. Aircraft operating with the ICAO 3LD assigned to a company or entity from a country listed as a State

Department−designated special interest country and holding valid FAA part 129 operations specifications do not

require FAA flight routing authorization.

d. FAA routing authorizations will only be granted for IFR operations. VFR and DVFR flight operations are

prohibited for any aircraft requiring an FAA routing authorization.

5−6−12. Emergency Security Control of Air Traffic (ESCAT)

a. During defense emergency or air defense emergency conditions, additional special security instructions

may be issued in accordance with 32 CFR part 245, Plan for the Emergency Security Control of Air Traffic

(ESCAT).

b. Under the provisions of 32 CFR part 245, the military will direct the action to be taken in regard to landing,

grounding, diversion, or dispersal of aircraft in the defense of the U.S. during emergency conditions.

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c. At the time a portion or all of ESCAT is implemented, ATC facilities will broadcast appropriate instructions

received from the Air Traffic Control System Command Center (ATCSCC) over available ATC frequencies.

Depending on instructions received from the ATCSCC, VFR flights may be directed to land at the nearest

available airport, and IFR flights will be expected to proceed as directed by ATC.

d. Pilots on the ground may be required to file a flight plan and obtain an approval (through FAA) prior to

conducting flight operation.

5−6−13. Interception Procedures

a. General.

1. In conjunction with the FAA, Air Defense Sectors monitor air traffic and could order an intercept in the

interest of national security or defense. Intercepts during peacetime operations are vastly different than those

conducted under increased states of readiness. The interceptors may be fighters or rotary wing aircraft. The

reasons for aircraft intercept include, but are not limited to:

(a) Identify an aircraft;

(b) Track an aircraft;

(d) Divert an aircraft;

(e) Establish communications with an aircraft.

2. When specific information is required (i.e., markings, serial numbers, etc.) the interceptor pilot(s) will

respond only if, in their judgment, the request can be conducted in a safe manner. Intercept procedures are

described in some detail in the paragraphs below. In all situations, the interceptor pilot will consider safety of

flight for all concerned throughout the intercept procedure. The interceptor pilot(s) will use caution to avoid

startling the intercepted crew or passengers and understand that maneuvers considered normal for interceptor

aircraft may be considered hazardous to other aircraft.

3. All aircraft operating in US national airspace are highly encouraged to maintain a listening watch on

VHF/UHF guard frequencies (121.5 or 243.0 MHz). If subjected to a military intercept, it is incumbent on

civilian aviators to understand their responsibilities and to comply with ICAO standard signals relayed from the

intercepting aircraft. Specifically, aviators are expected to contact air traffic control without delay (if able) on

the local operating frequency or on VHF/UHF guard. Noncompliance may result in the use of force.

b. Fighter intercept phases (see FIG 5−6−1).

1. Approach Phase.

As standard procedure, intercepted aircraft are approached from behind. Typically, interceptor aircraft will be

employed in pairs, however, it is not uncommon for a single aircraft to perform the intercept operation. Safe

separation between interceptors and intercepted aircraft is the responsibility of the intercepting aircraft and will

be maintained at all times.

2. Identification Phase.

Interceptor aircraft will initiate a controlled closure toward the aircraft of interest, holding at a distance no closer

than deemed necessary to establish positive identification and to gather the necessary information. The

interceptor may also fly past the intercepted aircraft while gathering data at a distance considered safe based on

aircraft performance characteristics.

3. Post Intercept Phase.

An interceptor may attempt to establish communications via standard ICAO signals. In time-critical situations

where the interceptor is seeking an immediate response from the intercepted aircraft or if the intercepted aircraft

remains non-compliant to instruction, the interceptor pilot may initiate a divert maneuver. In this maneuver, the

interceptor flies across the intercepted aircraft’s flight path (minimum 500 feet separation and commencing from

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slightly below the intercepted aircraft altitude) in the general direction the intercepted aircraft is expected to turn.

The interceptor will rock its wings (daytime) or flash external lights/select afterburners (night) while crossing

the intercepted aircraft’s flight path. The interceptor will roll out in the direction the intercepted aircraft is

expected to turn before returning to verify the aircraft of interest is complying. The intercepted aircraft is

expected to execute an immediate turn to the direction of the intercepting aircraft. If the aircraft of interest does

not comply, the interceptor may conduct a second climbing turn across the intercepted aircraft’s flight path

(minimum 500 feet separation and commencing from slightly below the intercepted aircraft altitude) while

expending flares as a warning signal to the intercepted aircraft to comply immediately and to turn in the direction

indicated and to leave the area. The interceptor is responsible to maintain safe separation during these and all

intercept maneuvers. Flight safety is paramount.

NOTE−

1. NORAD interceptors will take every precaution to preclude the possibility of the intercepted aircraft experiencing jet

wash/wake turbulence; however, there is a potential that this condition could be encountered.

2. During Night/IMC, the intercept will be from below flight path.

FIG 5−6−1

Intercept Procedures

c. Helicopter Intercept phases (see FIG 5−6−2).

1. Approach Phase. Aircraft intercepted by helicopter may be approached from any direction, although

the helicopter should close for identification and signaling from behind. Generally, the helicopter will approach

off the left side of the intercepted aircraft. Safe separation between the helicopter and the unidentified aircraft

will be maintained at all times.

2. Identification Phase. The helicopter will initiate a controlled closure toward the aircraft of interest,

holding at a distance no closer than deemed necessary to establish positive identification and gather the necessary

information. The intercepted pilot should expect the interceptor helicopter to take a position off his left wing

slightly forward of abeam.

3. Post Intercept Phase. Visual signaling devices may be used in an attempt to communicate with the

intercepted aircraft. Visual signaling devices may include, but are not limited to, LED scrolling signboards or

blue flashing lights. If compliance is not attained through the use of radios or signaling devices, standard ICAO

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2/20/25 AIM

intercept signals (TBL 5−6−1) may be employed. In order to maintain safe aircraft separation, it is incumbent

upon the pilot of the intercepted aircraft not to fall into a trail position (directly behind the helicopter) if instructed

to follow the helicopter. This is because the helicopter pilot may lose visual contact with the intercepted aircraft.

NOTE−

Intercepted aircraft must not follow directly behind the helicopter thereby allowing the helicopter pilot to maintain visual

contact with the intercepted aircraft and ensuring safe separation is maintained.

FIG 5−6−2

Helicopter Intercept Procedures

d. Summary of Intercepted Aircraft Actions. An intercepted aircraft must, without delay:

1. Adhere to instructions relayed through the use of visual devices, visual signals, and radio

communications from the intercepting aircraft.

2. Attempt to establish radio communications with the intercepting aircraft or with the appropriate air traffic

control facility by making a general call on guard frequencies (121.5 or 243.0 MHz), giving the identity, position,

and nature of the flight.

3. If transponder equipped, select Mode 3/A Code 7700 unless otherwise instructed by air traffic control.

NOTE−

If instruction received from any agency conflicts with that given by the intercepting aircraft through visual or radio

communications, the intercepted aircraft must seek immediate clarification.

4. The crew of the intercepted aircraft must continue to comply with interceptor aircraft signals and

instructions until positively released.

5−6−14. Interception Signals

TBL 5−6−1 and TBL 5−6−2.

National Security and Interception Procedures 5−6−11

AIM 2/20/25

TBL 5−6−1

Intercepting Signals

INTERCEPTING SIGNALS

Signals initiated by intercepting aircraft and responses by intercepted aircraft

(as set forth in ICAO Annex 2-Appendix 1, 2.1)

Series INTERCEPTING Aircraft Signals Meaning INTERCEPTED Aircraft Responds Meaning

1 DAY−Rocking wings from a position

slightly above and ahead of, and normally

to the left of, the intercepted aircraft and,

after acknowledgement, a slow level turn,

normally to the left, on to the desired

heading.

NIGHT-Same and, in addition, flashing

navigational lights at irregular intervals.

NOTE 1 −Meteorological conditions or

terrain may require the intercepting

aircraft to take up a position slightly above

and ahead of, and to the right of, the

intercepted aircraft and to make the

subsequent turn to the right.

NOTE 2−If the intercepted aircraft is not

able to keep pace with the intercepting

aircraft, the latter is expected to fly a series

of race−track patterns and to rock its wings

each time it passes the intercepted aircraft.

You have

been

intercepted.

Follow me.

AEROPLANES:

DAY−Rocking wings and following.

NIGHT−Same and, in addition, flashing

navigational lights at irregular intervals.

HELICOPTERS:

DAY or NIGHT−Rocking aircraft, flashing

navigational lights at irregular intervals and

following.

Understood,

will comply.

2 DAY or NIGHT− An abrupt break −away

maneuver from the intercepted aircraft

consisting of a climbing turn of 90 degrees

or more without crossing the line of flight

of the intercepted aircraft.

You may

proceed.

AEROPLANES:

DAY or NIGHT-Rocking wings.

HELICOPTERS:

DAY or NIGHT−Rocking aircraft.

Understood,

will comply.

3 DAY−Circling aerodrome, lowering land-

ing gear and overflying runway in direction

of landing or, if the intercepted aircraft is a

helicopter, overflying the helicopter land-

ing area.

NIGHT−Same and, in addition, showing

steady landing lights.

Land at this

aerodrome.

AEROPLANES:

DAY−Lowering landing gear, following

the intercepting aircraft and, if after

overflying the runway landing is consid-

ered safe, proceeding to land.

NIGHT−Same and, in addition, showing

steady landing lights (if carried).

HELICOPTERS:

DAY or NIGHT-Following the intercepting

aircraft and proceeding to land, showing a

steady landing light (if carried).

Understood,

will comply.

National Security and Interception Procedures 5−6−12

2/20/25 AIM

TBL 5−6−2

Intercepting Signals

INTERCEPTING SIGNALS

Signals and Responses During Aircraft Intercept

Signals initiated by intercepted aircraft and responses by intercepting aircraft

(as set forth in ICAO Annex 2-Appendix 1, 2.2)

Series INTERCEPTED Aircraft Signals Meaning INTERCEPTING Aircraft Responds Meaning

4 DAY or NIGHT−Raising landing gear (if

fitted) and flashing landing lights while

passing over runway in use or helicopter

landing area at a height exceeding 300m

(1,000 ft) but not exceeding 600m

(2,000 ft) (in the case of a helicopter, at a

height exceeding 50m (170 ft) but not

exceeding 100m (330 ft) above the

aerodrome level, and continuing to circle

runway in use or helicopter landing area. If

unable to flash landing lights, flash any

other lights available.

Aerodrome

you have

designated is

inadequate.

DAY or NIGHT− If it is desired that the

intercepted aircraft follow the intercepting

aircraft to an alternate aerodrome, the

intercepting aircraft raises its landing gear

(if fitted) and uses the Series 1 signals

prescribed for intercepting aircraft.

If it is decided to release the intercepted

aircraft, the intercepting aircraft uses the

Series 2 signals prescribed for intercepting

aircraft.

Understood,

follow me.

Understood,

you may

proceed.

5 DAY or NIGHT−Regular switching on and

off of all available lights but in such a

manner as to be distinct from flashing

lights.

Cannot

comply.

DAY or NIGHT-Use Series 2 signals

prescribed for intercepting aircraft.

Understood.

6 DAY or NIGHT−Irregular flashing of all

available lights.

In distress. DAY or NIGHT-Use Series 2 signals

prescribed for intercepting aircraft.

Understood.

National Security and Interception Procedures 5−6−13

AIM 2/20/25

5−6−14 National Security and Interception Procedures

5−6−15. ADIZ Boundaries and Designated Mountainous Areas (See FIG 5−6−3.)

FIG 5−6−3

Air Defense Identification Zone Boundaries

Designated Mountainous Areas

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � ��

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � ��

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

� � � � � � � � � � � � � ��

� � � � � � � � � � � � � � � � � � � � � � � � � � � � �

� � � � � � � � � � � � � � � � � � � � � � � � � � �

� � � �

� � � � � � � ��

2/20/25 AIM

5−6−16. Visual Warning System (VWS)

The VWS signal consists of highly-focused red and green colored laser lights designed to illuminate in an

alternating red and green signal pattern. These lasers may be directed at specific aircraft suspected of making

unauthorized entry into the Washington, DC Special Flight Rules Area (DC SFRA) proceeding on a heading or

flight path that may be interpreted as a threat or that operate contrary to the operating rules for the DC SFRA.

The beam is neither hazardous to the eyes of pilots/aircrew or passengers, regardless of altitude or distance from

the source nor will the beam affect aircraft systems.

a. If you are communicating with ATC, and this signal is directed at your aircraft, you are required to contact

ATC and advise that you are being illuminated by a visual warning system.

b. If this signal is directed at you, and you are not communicating with ATC, you are advised to turn to the

most direct heading away from the center of the DC SFRA as soon as possible. Immediately contact ATC on an

appropriate frequency, VHF Guard 121.5 or UHF Guard 243.0, and provide your aircraft identification, position,

and nature of the flight. Failure to follow these procedures may result in interception by military aircraft. Further

noncompliance with interceptor aircraft or ATC may result in the use of force.

c. Pilots planning to operate aircraft in or near the DC SFRA are to familiarize themselves with aircraft

intercept procedures. This information applies to all aircraft operating within the DC SFRA including DoD, Law

Enforcement, and aircraft engaged in aeromedical operations and does not change procedures established for

reporting unauthorized laser illumination as published in FAA Advisory Circulars and Notices.

REFERENCE−

CFR 91.161.

d. More details including a video demonstration of the VWS are available from the following FAA website:

www.faasafety.gov/VisualWarningSystem/VisualWarning.htm.

National Security and Interception Procedures 5−6−15

2/20/25 AIM

Chapter 6. Emergency Procedures

Section 1. General

6−1−1. Pilot Responsibility and Authority

a. The pilot−in−command of an aircraft is directly responsible for and is the final authority as to the operation

of that aircraft. In an emergency requiring immediate action, the pilot−in−command may deviate from any rule

in 14 CFR part 91, Subpart A, General, and Subpart B, Flight Rules, to the extent required to meet that emergency.

NOTE−

In the event of a pilot incapacitation, an Emergency Autoland system or an emergency descent system may assume operation

of the aircraft and deviate to meet that emergency.

REFERENCE−

14 CFR Section 91.3(b).

b. If the emergency authority of 14 CFR section 91.3(b) is used to deviate from the provisions of an ATC

clearance, the pilot−in−command must notify ATC as soon as possible and obtain an amended clearance.

c. Unless deviation is necessary under the emergency authority of 14 CFR section 91.3, pilots of IFR flights

experiencing two-way radio communications failure are expected to adhere to the procedures prescribed under

“IFR operations, two-way radio communications failure.”

REFERENCE−

14 CFR Section 91.185.

6−1−2. Emergency Condition − Request Assistance Immediately

a. An emergency can be either a distress or urgency condition as defined in the Pilot/Controller Glossary.

Pilots do not hesitate to declare an emergency when they are faced with distress conditions such as fire,

mechanical failure, or structural damage. However, some are reluctant to report an urgency condition when they

encounter situations which may not be immediately perilous, but are potentially catastrophic. An aircraft is in

at least an urgency condition the moment the pilot becomes doubtful about position, fuel endurance, weather,

or any other condition that could adversely affect flight safety. This is the time to ask for help, not after the

situation has developed into a distress condition.

b. Pilots who become apprehensive for their safety for any reason should request assistance immediately.

Ready and willing help is available in the form of radio, radar, direction finding stations and other aircraft. Delay

has caused accidents and cost lives. Safety is not a luxury! Take action!

General 6−1−1

2/20/25 AIM

Section 2. Emergency Services Available to Pilots

6−2−1. Radar Service for VFR Aircraft in Difficulty

a. Radar equipped ATC facilities can provide radar assistance and navigation service (vectors) to VFR aircraft

in difficulty when the pilot can talk with the controller, and the aircraft is within radar coverage. Pilots should

clearly understand that authorization to proceed in accordance with such radar navigational assistance does not

constitute authorization for the pilot to violate CFRs. In effect, assistance is provided on the basis that

navigational guidance information is advisory in nature, and the responsibility for flying the aircraft safely

remains with the pilot.

b. Experience has shown that many pilots who are not qualified for instrument flight cannot maintain control

of their aircraft when they encounter clouds or other reduced visibility conditions. In many cases, the controller

will not know whether flight into instrument conditions will result from ATC instructions. To avoid possible

hazards resulting from being vectored into IFR conditions, a pilot in difficulty should keep the controller advised

of the current weather conditions being encountered and the weather along the course ahead and observe the

following:

1. If a course of action is available which will permit flight and a safe landing in VFR weather conditions,

noninstrument rated pilots should choose the VFR condition rather than requesting a vector or approach that will

take them into IFR weather conditions; or

2. If continued flight in VFR conditions is not possible, the noninstrument rated pilot should so advise the

controller and indicating the lack of an instrument rating, declare a distress condition; or

3. If the pilot is instrument rated and current, and the aircraft is instrument equipped, the pilot should so

indicate by requesting an IFR flight clearance. Assistance will then be provided on the basis that the aircraft can

operate safely in IFR weather conditions.

6−2−2. Transponder Emergency Operation

a. When a distress or urgency condition is encountered, the pilot of an aircraft with a coded radar beacon

transponder, who desires to alert a ground radar facility, should squawk Mode 3/A, Code 7700/Emergency and

Mode C altitude reporting and then immediately establish communications with the ATC facility.

b. Radar facilities are equipped so that Code 7700 normally triggers an alarm or special indicator at all control

positions. Pilots should understand that they might not be within a radar coverage area. Therefore, they should

continue squawking Code 7700 and establish radio communications as soon as possible.

6−2−3. Intercept and Escort

a. The concept of airborne intercept and escort is based on the Search and Rescue (SAR) aircraft establishing

visual and/or electronic contact with an aircraft in difficulty, providing in-flight assistance, and escorting it to

a safe landing. If bailout, crash landing or ditching becomes necessary, SAR operations can be conducted without

delay. For most incidents, particularly those occurring at night and/or during instrument flight conditions, the

availability of intercept and escort services will depend on the proximity of SAR units with suitable aircraft on

alert for immediate dispatch. In limited circumstances, other aircraft flying in the vicinity of an aircraft in

difficulty can provide these services.

b. If specifically requested by a pilot in difficulty or if a distress condition is declared, SAR coordinators will

take steps to intercept and escort an aircraft. Steps may be initiated for intercept and escort if an urgency condition

is declared and unusual circumstances make such action advisable.

c. It is the pilot’s prerogative to refuse intercept and escort services. Escort services will normally be provided

to the nearest adequate airport. Should the pilot receiving escort services continue onto another location after

Emergency Services Available to Pilots 6−2−1

AIM 2/20/25

reaching a safe airport, or decide not to divert to the nearest safe airport, the escort aircraft is not obligated to

continue and further escort is discretionary. The decision will depend on the circumstances of the individual

incident.

6−2−4. Emergency Locator Transmitter (ELT)

a. General.

1. ELTs are required for most General Aviation airplanes.

REFERENCE−

14 CFR SECTION 91.207.

2. ELTs of various types were developed as a means of locating downed aircraft. These electronic, battery

operated transmitters operate on one of three frequencies. These operating frequencies are 121.5 MHz, 243.0

MHz, and the newer 406 MHz. ELTs operating on 121.5 MHz and 243.0 MHz are analog devices. The newer

406 MHz ELT is a digital transmitter that can be encoded with the owner’s contact information or aircraft data.

The latest 406 MHz ELT models can also be encoded with the aircraft’s position data which can help SAR forces

locate the aircraft much more quickly after a crash. The 406 MHz ELTs also transmits a stronger signal when

activated than the older 121.5 MHz ELTs.

(a) The Federal Communications Commission (FCC) requires 406 MHz ELTs be registered with the

National Oceanic and Atmospheric Administration (NOAA) as outlined in the ELTs documentation. The FAA’s

406 MHz ELT Technical Standard Order (TSO) TSO−C126 also requires that each 406 MHz ELT be registered

with NOAA. The reason is NOAA maintains the owner registration database for U.S. registered 406 MHz

alerting devices, which includes ELTs. NOAA also operates the United States’ portion of the Cospas −Sarsat

satellite distress alerting system designed to detect activated 406 MHz ELTs and other distress alerting devices.

(b) As of 2009, the Cospas−Sarsat system terminated monitoring and reception of the 121.5 MHz and

243.0 MHz frequencies. What this means for pilots is that those aircraft with only 121.5 MHz or 243.0 MHz

ELTs onboard will have to depend upon either a nearby air traffic control facility receiving the alert signal or an

overflying aircraft monitoring 121.5 MHz or 243.0 MHz detecting the alert and advising ATC.

decode the owner’s information and provide that data to the appropriate search and rescue (SAR) center. In the

United States, NOAA provides the alert data to the appropriate U.S. Air Force Rescue Coordination Center

(RCC) or U.S. Coast Guard Rescue Coordination Center. That RCC can then telephone or contact the owner to

verify the status of the aircraft. If the aircraft is safely secured in a hangar, a costly ground or airborne search is

avoided. In the case of an inadvertent 406 MHz ELT activation, the owner can deactivate the 406 MHz ELT. If

the 406 MHz ELT equipped aircraft is being flown, the RCC can quickly activate a search. 406 MHz ELTs permit

the Cospas−Sarsat satellite system to narrow the search area to a more confined area compared to that of a 121.5

MHz or 243.0 MHz ELT. 406 MHz ELTs also include a low −power 121.5 MHz homing transmitter to aid

searchers in finding the aircraft in the terminal search phase.

(d) Each analog ELT emits a distinctive downward swept audio tone on 121.5 MHz and 243.0 MHz.

(e) If “armed” and when subject to crash−generated forces, ELTs are designed to automatically activate

and continuously emit their respective signals, analog or digital. The transmitters will operate continuously for

at least 48 hours over a wide temperature range. A properly installed, maintained, and functioning ELT can

expedite search and rescue operations and save lives if it survives the crash and is activated.

(f) Pilots and their passengers should know how to activate the aircraft’s ELT if manual activation is

required. They should also be able to verify the aircraft’s ELT is functioning and transmitting an alert after a crash

or manual activation.

(g) Because of the large number of 121.5 MHz ELT false alerts and the lack of a quick means of verifying

the actual status of an activated 121.5 MHz or 243.0 MHz analog ELT through an owner registration database,

U.S. SAR forces do not respond as quickly to initial 121.5/243.0 MHz ELT alerts as the SAR forces do to 406

6−2−2 Emergency Services Available to Pilots

2/20/25 AIM

MHz ELT alerts. Compared to the almost instantaneous detection of a 406 MHz ELT, SAR forces’ normal

practice is to wait for confirmation of an overdue aircraft or similar notification. In some cases, this confirmation

process can take hours. SAR forces can initiate a response to 406 MHz alerts in minutes compared to the potential

delay of hours for a 121.5/243.0 MHz ELT. Therefore, due to the obvious advantages of 406 MHz beacons and

the significant disadvantages to the older 121.5/243.0 MHz beacons, and considering that the International

Cospas−Sarsat Program stopped the monitoring of 121.5/243.0 MHz by satellites on February 1, 2009, all aircraft

owners/operators are highly encouraged by both NOAA and the FAA to consider making the switch to a digital

406 MHz ELT beacon. Further, for non−aircraft owner pilots, check the ELT installed in the aircraft you are

flying, and as appropriate, obtain a personal locator beacon transmitting on 406 MHz.

b. Testing.

1. ELTs should be tested in accordance with the manufacturer’s instructions, preferably in a shielded or

screened room or specially designed test container to prevent the broadcast of signals which could trigger a false

alert.

2. When this cannot be done, aircraft operational testing is authorized as follows:

(a) Analog 121.5/243 MHz ELTs should only be tested during the first 5 minutes after any hour. If

operational tests must be made outside of this period, they should be coordinated with the nearest FAA Control

Tower. Tests should be no longer than three audible sweeps. If the antenna is removable, a dummy load should

be substituted during test procedures.

(b) Digital 406 MHz ELTs should only be tested in accordance with the unit’s manufacturer’s

instructions.

c. False Alarms.

1. Caution should be exercised to prevent the inadvertent activation of ELTs in the air or while they are being

handled on the ground. Accidental or unauthorized activation will generate an emergency signal that cannot be

distinguished from the real thing, leading to expensive and frustrating searches. A false ELT signal could also

interfere with genuine emergency transmissions and hinder or prevent the timely location of crash sites. Frequent

false alarms could also result in complacency and decrease the vigorous reaction that must be attached to all ELT

signals.

2. Numerous cases of inadvertent activation have occurred as a result of aerobatics, hard landings,

movement by ground crews and aircraft maintenance. These false alarms can be minimized by monitoring 121.5

MHz and/or 243.0 MHz as follows:

(a) In flight when a receiver is available.

(b) Before engine shut down at the end of each flight.

(d) When maintenance is being performed near the ELT.

(e) When a ground crew moves the aircraft.

(f) If an ELT signal is heard, turn off the aircraft’s ELT to determine if it is transmitting. If it has been

activated, maintenance might be required before the unit is returned to the “ARMED” position. You should

contact the nearest Air Traffic facility and notify it of the inadvertent activation.

d. Inflight Monitoring and Reporting.

1. Pilots are encouraged to monitor 121.5 MHz and/or 243.0 MHz while inflight to assist in identifying

possible emergency ELT transmissions. On receiving a signal, report the following information to the nearest

air traffic facility:

Emergency Services Available to Pilots 6−2−3

AIM 2/20/25

(a) Your position at the time the signal was first heard.

(b) Your position at the time the signal was last heard.

(d) Your flight altitudes and frequency on which the emergency signal was heard: 121.5 MHz or 243.0

MHz. If possible, positions should be given relative to a navigation aid. If the aircraft has homing equipment,

provide the bearing to the emergency signal with each reported position.

6−2−5. FAA K −9 Explosives Detection Team Program

a. The FAA’s Office of Civil Aviation Security Operations manages the FAA K−9 Explosives Detection Team

Program which was established in 1972. Through a unique agreement with law enforcement agencies and airport

authorities, the FAA has strategically placed FAA−certified K−9 teams (a team is one handler and one dog) at

airports throughout the country. If a bomb threat is received while an aircraft is in flight, the aircraft can be

directed to an airport with this capability. The FAA provides initial and refresher training for all handlers,

provides single purpose explosive detector dogs, and requires that each team is annually evaluated in five areas

for FAA certification: aircraft (widebody and narrowbody), vehicles, terminal, freight (cargo), and luggage. If

you desire this service, notify your company or an FAA air traffic control facility.

b. The following list shows the locations of current FAA K−9 teams:

TBL 6−2−1

FAA Sponsored Explosives Detection Dog/Handler Team Locations

Airport Symbol Location

ATL Atlanta, Georgia

BHM Birmingham, Alabama

BOS Boston, Massachusetts

BUF Buffalo, New York

CLT Charlotte, North Carolina

ORD Chicago, Illinois

CVG Cincinnati, Ohio

DFW Dallas, Texas

DEN Denver, Colorado

DTW Detroit, Michigan

IAH Houston, Texas

JAX Jacksonville, Florida

MCI Kansas City, Missouri

LAX Los Angeles, California

MEM Memphis, Tennessee

Airport Symbol Location

MIA Miami, Florida

MKE Milwaukee, Wisconsin

MSY New Orleans, Louisiana

MCO Orlando, Florida

PHX Phoenix, Arizona

PIT Pittsburgh, Pennsylvania

PDX Portland, Oregon

SLC Salt Lake City, Utah

SFO San Francisco, California

SJU San Juan, Puerto Rico

SEA Seattle, Washington

STL St. Louis, Missouri

TUS Tucson, Arizona

TUL Tulsa, Oklahoma

c. If due to weather or other considerations an aircraft with a suspected hidden explosive problem were to land

or intended to land at an airport other than those listed in b above, it is recommended that they call the FAA’s

Washington Operations Center (telephone 202−267−3333, if appropriate) or have an air traffic facility with

which you can communicate contact the above center requesting assistance.

6−2−6. Search and Rescue

a. General. SAR is a lifesaving service provided through the combined efforts of the federal agencies

signatory to the National SAR Plan, and the agencies responsible for SAR within each state. Operational

resources are provided by the U.S. Coast Guard, DoD components, the Civil Air Patrol, the Coast Guard

Auxiliary, state, county and local law enforcement and other public safety agencies, and private volunteer

6−2−4 Emergency Services Available to Pilots

2/20/25 AIM

organizations. Services include search for missing aircraft, survival aid, rescue, and emergency medical help for

the occupants after an accident site is located.

b. National Search and Rescue Plan. By federal interagency agreement, the National Search and Rescue

Plan provides for the effective use of all available facilities in all types of SAR missions. These facilities include

aircraft, vessels, pararescue and ground rescue teams, and emergency radio fixing. Under the plan, the U.S. Coast

Guard is responsible for the coordination of SAR in the Maritime Region, and the USAF is responsible in the

Inland Region. To carry out these responsibilities, the Coast Guard and the Air Force have established Rescue

Coordination Centers (RCCs) to direct SAR activities within their regions. For aircraft emergencies, distress,

and urgency, information normally will be passed to the appropriate RCC through an ARTCC or FSS.

c. Coast Guard Rescue Coordination Centers. (See TBL 6−2−2.)

TBL 6−2−2

Coast Guard Rescue Coordination Centers

Alameda, CA

510−437−3701

Miami, FL

305−415−6800

Boston, MA

617−223−8555

New Orleans, LA

504−589−6225

Cleveland, OH

216−902−6117

Portsmouth, V A

757−398−6390

Honolulu, HI

808−541−2500

Seattle, WA

206−220−7001

Juneau, AK

907−463−2000

San Juan, PR

787−289−2042

d. Air Force Rescue Coordination Centers. (See TBL 6−2−3 and TBL 6−2−4.)

TBL 6−2−3

Air Force Rescue Coordination Center

48 Contiguous States

Air Force Rescue Coordination Center

Tyndall AFB, Florida Phone

Commercial 850−283−5955

WATS 800−851−3051

DSN 523−5955

TBL 6−2−4

Air Command Rescue Coordination Center

Alaska

Alaskan Air Command Rescue

Coordination Center

Elmendorf AFB, Alaska Phone

Commercial 907−428−7230

800−420−7230

(outside Anchorage)

DSN 317−551−7230

e. Joint Rescue Coordination Center. (See TBL 6−2−5.)

Emergency Services Available to Pilots 6−2−5

AIM 2/20/25

TBL 6−2−5

Joint Rescue Coordination Center

Hawaii

Honolulu Joint Rescue Coordination Center

HQ 14th CG District

Honolulu Phone

Commercial 808−541−2500

DSN 448−0301

f. Emergency and Overdue Aircraft.

1. ARTCCs and FSSs will alert the SAR system when information is received from any source that an

aircraft is in difficulty, overdue, or missing.

(a) Radar facilities providing radar flight following or advisories consider the loss of radar and radios,

without service termination notice, to be a possible emergency. Pilots receiving VFR services from radar

facilities should be aware that SAR may be initiated under these circumstances.

(b) A filed flight plan is the most timely and effective indicator that an aircraft is overdue. Flight plan

information is invaluable to SAR forces for search planning and executing search efforts.

2. Prior to departure on every flight, local or otherwise, someone at the departure point should be advised

of your destination and route of flight if other than direct. Search efforts are often wasted and rescue is often

delayed because of pilots who thoughtlessly takeoff without telling anyone where they are going. File a flight

plan for your safety.

3. According to the National Search and Rescue Plan, “The life expectancy of an injured survivor decreases

as much as 80 percent during the first 24 hours, while the chances of survival of uninjured survivors rapidly

diminishes after the first 3 days.”

4. An Air Force Review of 325 SAR missions conducted during a 23−month period revealed that “Time

works against people who experience a distress but are not on a flight plan, since 36 hours normally pass before

family concern initiates an (alert).”

g. VFR Search and Rescue Protection.

1. To receive this valuable protection, file a VFR or DVFR Flight Plan with an FAA FSS. For maximum

protection, file only to the point of first intended landing, and refile for each leg to final destination. When a

lengthy flight plan is filed, with several stops en route and an ETE to final destination, a mishap could occur on

any leg, and unless other information is received, it is probable that no one would start looking for you until 30

minutes after your ETA at your final destination.

2. If you land at a location other than the intended destination, report the landing to the nearest FAA FSS

and advise them of your original destination.

3. If you land en route and are delayed more than 30 minutes, report this information to the nearest FSS and

give them your original destination.

4. If your ETE changes by 30 minutes or more, report a new ETA to the nearest FSS and give them your

original destination. Remember that if you fail to respond within one-half hour after your ETA at final

destination, a search will be started to locate you.

5. It is important that you close your flight plan IMMEDIATELY AFTER ARRIVAL AT YOUR FINAL

DESTINATION WITH THE FSS DESIGNATED WHEN YOUR FLIGHT PLAN WAS FILED. The pilot is

responsible for closure of a VFR or DVFR flight plan; they are not closed automatically. This will prevent

needless search efforts.

6. The rapidity of rescue on land or water will depend on how accurately your position may be determined.

If a flight plan has been followed and your position is on course, rescue will be expedited.

6−2−6 Emergency Services Available to Pilots

2/20/25 AIM

h. Survival Equipment.

1. For flight over uninhabited land areas, it is wise to take and know how to use survival equipment for the

type of climate and terrain.

2. If a forced landing occurs at sea, chances for survival are governed by the degree of crew proficiency in

emergency procedures and by the availability and effectiveness of water survival equipment.

i. Body Signal Illustrations.

1. If you are forced down and are able to attract the attention of the pilot of a rescue airplane, the body signals

illustrated on these pages can be used to transmit messages to the pilot circling over your location.

2. Stand in the open when you make the signals.

3. Be sure the background, as seen from the air, is not confusing.

4. Go through the motions slowly and repeat each signal until you are positive that the pilot understands

you.

j. Observance of Downed Aircraft.

1. Determine if crash is marked with a yellow cross; if so, the crash has already been reported and identified.

2. If possible, determine type and number of aircraft and whether there is evidence of survivors.

3. Fix the position of the crash as accurately as possible with reference to a navigational aid. If possible,

provide geographic or physical description of the area to aid ground search parties.

4. Transmit the information to the nearest FAA or other appropriate radio facility.

5. If circumstances permit, orbit the scene to guide in other assisting units until their arrival or until you are

relieved by another aircraft.

6. Immediately after landing, make a complete report to the nearest FAA facility, or Air Force or Coast

Guard Rescue Coordination Center. The report can be made by a long distance collect telephone call.

Emergency Services Available to Pilots 6−2−7

NO.

AIM 2/20/25

FIG 6−2−1

Ground−Air Visual Code for Use by Survivors

NO. MESSAGEMESSAGE CODE SYMBOLCODE SYMBOL

1 Require assistanceRequire assistance V

2 Require medical assistanceRequire medical assistance X

3 No or NegativeNo or Negative N

4 Yes or AffirmativeYes or Affirmative Y

5 Proceeding in this directionProceeding in this direction

IF IN DOUBT, USE INTERNATIONAL SYMBOLIF IN DOUBT, USE INTERNATIONAL SYMBOL S O S

INSTRUCTIONSINSTRUCTIONS

1. Lay out symbols by using strips of fabric or parachutes, pieces of wood, stones, or any available material.

2. Provide as much color contrast as possible between material used for symbols and background against which symbols are exposed.

3. Symbols should be at least 10 feet high or larger. Care should be taken to lay out symbols exactly as shown.

4. In addition to using symbols, every effort is to be made to attract attention by means of radio, flares, smoke, or other available means.

5. On snow covered ground, signals can be made by dragging, shoveling or tramping. Depressed areas forming symbols will

appear black from the air.

6. Pilot should acknowledge message by rocking wings from side to side.

FIG 6−2−2

Ground−Air Visual Code for use by Ground Search Parties

CODE SYMBOLCODE SYMBOLNO. MESSAGEMESSAGE

1 Operation completed.Operation completed. L L L

2 L LWe have found all personnel.We have found all personnel.

3 We have found only some personnel.We have found only some personnel.

We are not able to continue.We are not able to continue.4 X XReturning to base.Returning to base.

Have divided into two groups.Have divided into two groups.5 Each proceeding in direction indicated.Each proceeding in direction indicated.

6 Information received that aircraft is in this direction.Information received that aircraft is in this direction.

7 Nothing found. Will continue search.Nothing found. Will continue search. N N

Note: These visual signals have been accepted for international use and appear in Annex 12 to the Convention on International

Civil Aviation.

Emergency Services Available to Pilots6−2−8

2/20/25 AIM

FIG 6−2−3

Urgent Medical Assistance

NEED MEDICAL

ASSISTANCE-URGENT

Used only when life is at stake

NEED MEDICAL

ASSISTANCE-URGENT

Used only when life is at stake

FIG 6−2−4

All OK

ALL OK-DO NOT WAIT

Wave one arm overhead

ALL OK-DO NOT WAIT

Wave one arm overhead

Emergency Services Available to Pilots 6−2−9

AIM 2/20/25

FIG 6−2−5

Short Delay

CAN PROCEED SHORTLY

WAIT IF PRACTICABLE

One arm horizontal

CAN PROCEED SHORTLY

WAIT IF PRACTICABLE

One arm horizontal

FIG 6−2−6

Long Delay

NEED MECHANICAL HELP

OR PARTS - LONG DELAY

Both arms horizontal

NEED MECHANICAL HELP

OR PARTS - LONG DELAY

Both arms horizontal

6−2−10 Emergency Services Available to Pilots

2/20/25 AIM

FIG 6−2−7

Drop Message

Make throwing motion

FIG 6−2−8

Receiver Operates

OUR RECEIVER IS

OPERATING

Cup hands over ears

OUR RECEIVER IS

OPERATING

Cup hands over ears

Emergency Services Available to Pilots 6−2−11

AIM 2/20/25

FIG 6−2−9

Do Not Land Here

DO NOT ATTEMPT

TO LAND HERE

Both arms waved across face

DO NOT ATTEMPT

TO LAND HERE

Both arms waved across face

FIG 6−2−10

Land Here

LAND HERE

Both arms forward horizontally,

squatting and point in direction

of landing - Repeat

LAND HERE

Both arms forward horizontally,

squatting and point in direction

of landing - Repeat

6−2−12 Emergency Services Available to Pilots

2/20/25 AIM

FIG 6−2−11

Negative (Ground)

NEGATIVE (NO)

White cloth waved horizontally

NEGATIVE (NO)

White cloth waved horizontally

FIG 6−2−12

Affirmative (Ground)

AFFIRMATIVE (YES)

White cloth waved vertically

AFFIRMATIVE (YES)

White cloth waved vertically

Emergency Services Available to Pilots 6−2−13

AIM 2/20/25

FIG 6−2−13

Pick Us Up

PICK US UP-

PLANE ABANDONED

Both arms vertical

PICK US UP-

PLANE ABANDONED

Both arms vertical

FIG 6−2−14

Affirmative (Aircraft)

Affirmative reply from aircraft:

AFFIRMATIVE (YES)

Dip nose of plane several times

6−2−14 Emergency Services Available to Pilots

2/20/25 AIM

FIG 6−2−15

Negative (Aircraft)

Negative reply from aircraft:Negative reply from aircraft:

NEGATIVE (NO)NEGATIVE (NO)

Fishtail planeFishtail plane

FIG 6−2−16

Message received and understood (Aircraft)

Message received and understood by aircraft:Message received and understood by aircraft:

Day or moonlight - Rocking wingsDay or moonlight - Rocking wings

Night - Green flashed from signal lampNight - Green flashed from signal lamp

Emergency Services Available to Pilots 6−2−15

AIM 2/20/25

6−2−16 Emergency Services Available to Pilots

FIG 6−2−17

Message received and NOT understood (Aircraft)

Message received and NOT understood by aircraft:

Day or moonlight - Making a complete right-hand circle

Night-Red flashes from signal lamp.

Message received and NOT understood by aircraft:

Day or moonlight - Making a complete right-hand circle

Night-Red flashes from signal lamp.

2/20/25 AIM

Section 3. Distress and Urgency Procedures

6−3−1. Distress and Urgency Communications

a. A pilot who encounters a distress or urgency condition can obtain assistance simply by contacting the air

traffic facility or other agency in whose area of responsibility the aircraft is operating, stating the nature of the

difficulty, pilot’s intentions and assistance desired. Distress and urgency communications procedures are

prescribed by the International Civil Aviation Organization (ICAO), however, and have decided advantages over

the informal procedure described above.

b. Distress and urgency communications procedures discussed in the following paragraphs relate to the use

of air ground voice communications.

c. The initial communication, and if considered necessary, any subsequent transmissions by an aircraft in

distress should begin with the signal MAYDAY , preferably repeated three times. The signal PAN−PAN should

be used in the same manner for an urgency condition.

d. Distress communications have absolute priority over all other communications, and the word MAYDAY

commands radio silence on the frequency in use. Urgency communications have priority over all other

communications except distress, and the word PAN−PAN warns other stations not to interfere with urgency

transmissions.

e. Normally, the station addressed will be the air traffic facility or other agency providing air traffic services,

on the frequency in use at the time. If the pilot is not communicating and receiving services, the station to be called

will normally be the air traffic facility or other agency in whose area of responsibility the aircraft is operating,

on the appropriate assigned frequency. If the station addressed does not respond, or if time or the situation

dictates, the distress or urgency message may be broadcast, or a collect call may be used, addressing “Any Station

(Tower)(Radio)(Radar).”

f. The station addressed should immediately acknowledge a distress or urgency message, provide assistance,

coordinate and direct the activities of assisting facilities, and alert the appropriate search and rescue coordinator

if warranted. Responsibility will be transferred to another station only if better handling will result.

g. All other stations, aircraft and ground, will continue to listen until it is evident that assistance is being

provided. If any station becomes aware that the station being called either has not received a distress or urgency

message, or cannot communicate with the aircraft in difficulty, it will attempt to contact the aircraft and provide

assistance.

h. Although the frequency in use or other frequenc ies assigned by ATC are preferable, the following

emergency frequencies can be used for distress or urgency communications, if necessary or desirable:

121.5 MHz and 243.0 MHz. Both have a range generally limited to line of sight. 121.5 MHz is guarded by

direction finding stations and some military and civil aircraft. 243.0 MHz is guarded by military aircraft. Both

121.5 MHz and 243.0 MHz are guarded by military towers, most civil towers, and radar facilities. Normally

ARTCC emergency frequency capability does not extend to radar coverage limits. If an ARTCC does not respond

when called on 121.5 MHz or 243.0 MHz, call the nearest tower.

6−3−2. Obtaining Emergency Assistance

a. A pilot in any distress or urgency condition should immediately take the following action, not necessarily

in the order listed, to obtain assistance:

1. Climb, if possible, for improved communications, and better radar and direction finding detection.

However, it must be understood that unauthorized climb or descent under IFR conditions within controlled

airspace is prohibited, except as permitted by 14 CFR section 91.3(b).

Distress and Urgency Procedures 6−3−1

AIM 2/20/25

2. If equipped with a radar beacon transponder (civil) or IFF/SIF (military):

(a) Continue squawking assigned Mode A/3 discrete code/VFR code and Mode C altitude encoding when

in radio contact with an air traffic facility or other agency providing air traffic services, unless instructed to do

otherwise.

(b) If unable to immediately establish communications with an air traffic facility/agency, squawk Mode

A/3, Code 7700/Emergency and Mode C.

3. Transmit a distress or urgency message consisting of as many as necessary of the following elements,

preferably in the order listed:

(a) If distress, MAYDAY , MAYDAY , MAY−DAY; if urgency, PAN−PAN, PAN−PAN, PAN−PAN.

(b) Name of station addressed.

(d) Nature of distress or urgency.

(e) Weather.

(f) Pilots intentions and request.

(g) Present position, and heading; or if lost, last known position, time, and heading since that position.

(h) Altitude or flight level.

(i) Fuel remaining in minutes.

(j) Number of people on board.

(k) Any other useful information.

REFERENCE−

Pilot/Controller Glossary Term− Fuel Remaining.

b. After establishing radio contact, comply with advice and instructions received. Cooperate. Do not hesitate

to ask questions or clarify instructions when you do not understand or if you cannot comply with clearance. Assist

the ground station to control communications on the frequency in use. Silence interfering radio stations. Do not

change frequency or change to another ground station unless absolutely necessary. If you do, advise the ground

station of the new frequency and station name prior to the change, transmitting in the blind if necessary. If

two−way communications cannot be established on the new frequency, return immediately to the frequency or

station where two−way communications last existed.

c. When in a distress condition with bailout, crash landing or ditching imminent, take the following additional

actions to assist search and rescue units:

1. Time and circumstances permitting, transmit as many as necessary of the message elements in

subparagraph a3 above, and any of the following that you think might be helpful:

(a) ELT status.

(b) Visible landmarks.

(d) Number of persons on board.

(e) Emergency equipment on board.

2. Actuate your ELT if the installation permits.

3. For bailout, and for crash landing or ditching if risk of fire is not a consideration, set your radio for

continuous transmission.

4. If it becomes necessary to ditch, make every effort to ditch near a surface vessel. If time permits, an FAA

facility should be able to get the position of the nearest commercial or Coast Guard vessel from a Coast Guard

Rescue Coordination Center.

6−3−2 Distress and Urgency Procedures

2/20/25 AIM

5. After a crash landing, unless you have good reason to believe that you will not be located by search

aircraft or ground teams, it is best to remain with your aircraft and prepare means for signaling search aircraft.

6−3−3. Ditching Procedures

FIG 6−3−1

Single Swell (15 knot wind)

SWELLSWELL

DITCHING

HEADING

WIND

FIG 6−3−2

Double Swell (15 knot wind)

PRIMARY

SWELL

PRIMARY

SWELL

SECONDARY

SWELL

SECONDARY

SWELL

HEADING

WIND

DITCHING

Distress and Urgency Procedures 6−3−3

AIM 2/20/25

FIG 6−3−3

Double Swell (30 knot wind)

PRIMARY

SWELL

PRIMARY

SWELL

SECONDARY

SWELL

SECONDARY

SWELL

WIND

DITCHING

HEADING

FIG 6−3−4

(50 knot wind)

SWELLSWELL

WINDWIND

Aircraft with low landing speeds - land into the wind.

Aircraft with high landing speeds - choose compromise

heading between wind and swell.

Both - land on back side of swell.

6−3−4 Distress and Urgency Procedures

2/20/25 AIM

FIG 6−3−5

Wind−Swell−Ditch Heading

GOOD FAIR

BESTBEST

DIRECTION OF

SWELL MOVEMENT

GOOD

Landing parallel to the major swell

GOOD !!

BACK SIDE

POOR!!!

FACE

Landing on the face and back of swell

a. A successful aircraft ditching is dependent on three primary factors. In order of importance they are:

1. Sea conditions and wind.

2. Type of aircraft.

3. Skill and technique of pilot.

b. Common oceanographic terminology.

1. Sea. The condition of the surface that is the result of both waves and swells.

2. Wave (or Chop). The condition of the surface caused by the local winds.

3. Swell. The condition of the surface which has been caused by a distance disturbance.

4. Swell Face. The side of the swell toward the observer. The backside is the side away from the observer.

These definitions apply regardless of the direction of swell movement.

5. Primary Swell. The swell system having the greatest height from trough to crest.

6. Secondary Swells. Those swell systems of less height than the primary swell.

7. Fetch. The distance the waves have been driven by a wind blowing in a constant direction, without

obstruction.

8. Swell Period. The time interval between the passage of two successive crests at the same spot in the

water, measured in seconds.

9. Swell Velocity. The speed and direction of the swell with relation to a fixed reference point, measured

in knots. There is little movement of water in the horizontal direction. Swells move primarily in a vertical motion,

similar to the motion observed when shaking out a carpet.

10. Swell Direction. The direction from which a swell is moving. This direction is not necessarily the result

of the wind present at the scene. The swell may be moving into or across the local wind. Swells, once set in

Distress and Urgency Procedures 6−3−5

AIM 2/20/25

motion, tend to maintain their original direction for as long as they continue in deep water, regardless of changes

in wind direction.

11. Swell Height. The height between crest and trough, measured in feet. The vast majority of ocean swells

are lower than 12 to 15 feet, and swells over 25 feet are not common at any spot on the oceans. Successive swells

may differ considerably in height.

c. In order to select a good heading when ditching an aircraft, a basic evaluation of the sea is required.

Selection of a good ditching heading may well minimize damage and could save your life. It can be extremely

dangerous to land into the wind without regard to sea conditions; the swell system, or systems, must be taken

into consideration. Remember one axiom− AVOID THE FACE OF A SWELL.

1. In ditching parallel to the swell, it makes little difference whether touchdown is on the top of the crest

or in the trough. It is preferable, however, to land on the top or back side of the swell, if possible. After

determining which heading (and its reciprocal) will parallel the swell, select the heading with the most into the

wind component.

2. If only one swell system exists, the problem is relatively simple −even with a high, fast system.

Unfortunately, most cases involve two or more swell systems running in different directions. With more than one

system present, the sea presents a confused appearance. One of the most difficult situations occurs when two

swell systems are at right angles. For example, if one system is eight feet high, and the other three feet, plan to

land parallel to the primary system, and on the down swell of the secondary system. If both systems are of equal

height, a compromise may be advisable−select an intermediate heading at 45 degrees down swell to both systems.

When landing down a secondary swell, attempt to touch down on the back side, not on the face of the swell.

3. If the swell system is formidable, it is considered advisable, in landplanes, to accept more crosswind in

order to avoid landing directly into the swell.

4. The secondary swell system is often from the same direction as the wind. Here, the landing may be made

parallel to the primary system, with the wind and secondary system at an angle. There is a choice to two directions

paralleling the primary system. One direction is downwind and down the secondary swell, and the other is into

the wind and into the secondary swell, the choice will depend on the velocity of the wind versus the velocity and

height of the secondary swell.

d. The simplest method of estimating the wind direction and velocity is to examine the windstreaks on the

water. These appear as long streaks up and down wind. Some persons may have difficulty determining wind

direction after seeing the streaks on the water. Whitecaps fall forward with the wind but are overrun by the waves

thus producing the illusion that the foam is sliding backward. Knowing this, and by observing the direction of

the streaks, the wind direction is easily determined. Wind velocity can be estimated by noting the appearance

of the whitecaps, foam and wind streaks.

1. The behavior of the aircraft on making contact with the water will vary within wide limits according to

the state of the sea. If landed parallel to a single swell system, the behavior of the aircraft may approximate that

to be expected on a smooth sea. If landed into a heavy swell or into a confused sea, the deceleration forces may

be extremely great−resulting in breaking up of the aircraft. Within certain limits, the pilot is able to minimize

these forces by proper sea evaluation and selection of ditching heading.

2. When on final approach the pilot should look ahead and observe the surface of the sea. There may be

shadows and whitecaps−signs of large seas. Shadows and whitecaps close together indicate short and rough seas.

Touchdown in these areas is to be avoided. Select and touchdown in any area (only about 500 feet is needed)

where the shadows and whitecaps are not so numerous.

3. Touchdown should be at the lowest speed and rate of descent which permit safe handling and optimum

nose up attitude on impact. Once first impact has been made, there is often little the pilot can do to control a

landplane.

e. Once preditching preparations are completed, the pilot should turn to the ditching heading and commence

let−down. The aircraft should be flown low over the water, and slowed down until ten knots or so above stall.

6−3−6 Distress and Urgency Procedures

2/20/25 AIM

At this point, additional power should be used to overcome the increased drag caused by the nose up attitude.

When a smooth stretch of water appears ahead, cut power, and touchdown at the best recommended speed as fully

stalled as possible. By cutting power when approaching a relatively smooth area, the pilot will prevent

overshooting and will touchdown with less chance of planing off into a second uncontrolled landing. Most

experienced seaplane pilots prefer to make contact with the water in a semi−stalled attitude, cutting power as the

tail makes contact. This technique eliminates the chance of misjudging altitude with a resultant heavy drop in

a fully stalled condition. Care must be taken not to drop the aircraft from too high altitude or to balloon due to

excessive speed. The altitude above water depends on the aircraft. Over glassy smooth water, or at night without

sufficient light, it is very easy, for even the most experienced pilots to misjudge altitude by 50 feet or more. Under

such conditions, carry enough power to maintain nine to twelve degrees nose up attitude, and 10 to 20 percent

over stalling speed until contact is made with the water. The proper use of power on the approach is of great

importance. If power is available on one side only, a little power should be used to flatten the approach; however,

the engine should not be used to such an extent that the aircraft cannot be turned against the good engines right

down to the stall with a margin of rudder movement available. When near the stall, sudden application of

excessive unbalanced power may result in loss of directional control. If power is available on one side only, a

slightly higher than normal glide approach speed should be used. This will ensure good control and some margin

of speed after leveling off without excessive use of power. The use of power in ditching is so important that when

it is certain that the coast cannot be reached, the pilot should, if possible, ditch before fuel is exhausted. The use

of power in a night or instrument ditching is far more essential than under daylight contact conditions.

1. If no power is available, a greater than normal approach speed should be used down to the flare−out. This

speed margin will allow the glide to be broken early and more gradually, thereby giving the pilot time and distance

to feel for the surface − decreasing the possibility of stalling high or flying into the water. When landing parallel

to a swell system, little difference is noted between landing on top of a crest or in the trough. If the wings of aircraft

are trimmed to the surface of the sea rather than the horizon, there is little need to worry about a wing hitting a

swell crest. The actual slope of a swell is very gradual. If forced to land into a swell, touchdown should be made

just after passage of the crest. If contact is made on the face of the swell, the aircraft may be swamped or thrown

violently into the air, dropping heavily into the next swell. If control surfaces remain intact, the pilot should

attempt to maintain the proper nose above the horizon attitude by rapid and positive use of the controls.

f. After T ouchdown. In most cases drift, caused by crosswind can be ignored; the forces acting on the aircraft

after touchdown are of such magnitude that drift will be only a secondary consideration. If the aircraft is under

good control, the “crab” may be kicked out with rudder just prior to touchdown. This is more important with high

wing aircraft, for they are laterally unstable on the water in a crosswind and may roll to the side in ditching.

REFERENCE−

This information has been extracted from Appendix H of the “National Search and Rescue Manual.”

6−3−4. Special Emergency (Air Piracy)

a. A special emergency is a condition of air piracy, or other hostile act by a person(s) aboard an aircraft, which

threatens the safety of the aircraft or its passengers.

b. The pilot of an aircraft reporting a special emergency condition should:

1. If circumstances permit, apply distress or urgency radio−telephony procedures. Include the details of the

special emergency.

REFERENCE−

AIM, Para 6−3−1, Distress and Urgency Communications.

2. If circumstances do not permit the use of prescribed distress or urgency procedures, transmit:

(a) On the air/ground frequency in use at the time.

(b) As many as possible of the following elements spoken distinctly and in the following order:

(1) Name of the station addressed (time and circumstances permitting).

Distress and Urgency Procedures 6−3−7

AIM 2/20/25

(2) The identification of the aircraft and present position.

(3) The nature of the special emergency condition and pilot intentions (circumstances permitting).

(4) If unable to provide this information, use code words and/or transponder as follows:

Spoken Words

TRANSPONDER SEVEN FIVE ZERO ZERO

Meaning

I am being hijacked/forced to a new destination

Transponder Setting

Mode 3/A, Code 7500

NOTE−

Code 7500 will never be assigned by ATC without prior notification from the pilot that the aircraft is being subjected to

unlawful interference. The pilot should refuse the assignment of Code 7500 in any other situation and inform the controller

accordingly. Code 7500 will trigger the special emergency indicator in all radar ATC facilities.

c. Air traffic controllers will acknowledge and confirm receipt of transponder Code 7500 by asking the pilot

to verify it. If the aircraft is not being subjected to unlawful interference, the pilot should respond to the query

by broadcasting in the clear that the aircraft is not being subjected to unlawful interference. Upon receipt of this

information, the controller will request the pilot to verify the code selection depicted in the code selector windows

in the transponder control panel and change the code to the appropriate setting. If the pilot replies in the

affirmative or does not reply, the controller will not ask further questions but will flight follow, respond to pilot

requests and notify appropriate authorities.

d. If it is possible to do so without jeopardizing the safety of the flight, the pilot of a hijacked passenger aircraft,

after departing from the cleared routing over which the aircraft was operating, will attempt to do one or more

of the following things, insofar as circumstances may permit:

1. Maintain a true airspeed of no more than 400 knots, and preferably an altitude of between 10,000 and

25,000 feet.

2. Fly a course toward the destination which the hijacker has announced.

e. If these procedures result in either radio contact or air intercept, the pilot will attempt to comply with any

instructions received which may direct the aircraft to an appropriate landing field or alter the aircraft’s flight path

off its current course, away from protected airspace.

6−3−5. Fuel Dumping

a. Should it become necessary to dump fuel, the pilot should immediately advise ATC. Upon receipt of

information that an aircraft will dump fuel, ATC will broadcast or cause to be broadcast immediately and every

3 minutes thereafter the following on appropriate ATC and FSS radio frequencies:

EXAMPLE−

Attention all aircraft − fuel dumping in progress over − (location) at (altitude) by (type aircraft) (flight direction).

b. Upon receipt of such a broadcast, pilots of aircraft affected, which are not on IFR flight plans or special

VFR clearances, should clear the area specified in the advisory. Aircraft on IFR flight plans or special VFR

clearances will be provided specific separation by ATC. At the termination of the fuel dumping operation, pilots

should advise ATC. Upon receipt of such information, ATC will issue, on the appropriate frequencies, the

following:

EXAMPLE−

ATTENTION ALL AIRCRAFT − FUEL DUMPING BY − (type aircraft) − TERMINATED.

6−3−8 Distress and Urgency Procedures

2/20/25 AIM

Section 4. Two-way Radio Communications Failure

6−4−1. Two-way Radio Communications Failure

a. It is virtually impossible to provide regulations an d procedures applicable to all possible situations

associated with two-way radio communications failure. During two-way radio communications failure, when

confronted by a situation not covered in the regulation, pilots are expected to exercise good judgment in whatever

action they elect to take. Should the situation so dictate they should not be reluctant to use the emergency action

contained in 14 CFR section 91.3(b).

b. Whether two-way communications failure constitutes an emergency depends on the circumstances, and in

any event, it is a determination made by the pilot. 14 CFR section 91.3(b) authorizes a pilot to deviate from any

rule in Subparts A and B to the extent required to meet an emergency.

c. In the event of two-way radio communications failure, ATC service will be provided on the basis that the

pilot is operating in accordance with 14 CFR section 91.185. A pilot experiencing two-way communications

failure should (unless emergency authority is exercised) comply with 14 CFR section 91.185 quoted below:

1. General. Unless otherwise authorized by ATC, each pilot who has two-way radio communications

failure when operating under IFR must comply with the rules of this section.

2. VFR conditions. If the failure occurs in VFR conditions, or if VFR conditions are encountered after the

failure, each pilot must continue the flight under VFR and land as soon as practicable.

NOTE−

This procedure also applies when two-way radio failure occurs while operating in Class A airspace. The primary objective

of this provision in 14 CFR section 91.185 is to preclude extended IFR operation by these aircraft within the ATC system.

Pilots should recognize that operation under these conditions may unnecessarily as well as adversely affect other users of

the airspace, since ATC may be required to reroute or delay other users in order to protect the failure aircraft. However, it

is not intended that the requirement to “land as soon as practicable” be construed to mean “as soon as possible.” Pilots

retain the prerogative of exercising their best judgment and are not required to land at an unauthorized airport, at an airport

unsuitable for the type of aircraft flown, or to land only minutes short of their intended destination.

3. IFR conditions. If the failure occurs in IFR conditions, or if subparagraph 2 above cannot be complied

with, each pilot must continue the flight according to the following:

(a) Route.

(1) By the route assigned in the last ATC clearance received;

(2) If being radar vectored, by the direct route from the point of radio failure to the fix, route, or airway

specified in the vector clearance;

(3) In the absence of an assigned route, by the route that ATC has advised may be expected in a further

clearance; or

(4) In the absence of an assigned route or a route that ATC has advised may be expected in a further

clearance by the route filed in the flight plan.

(b) Altitude. At the HIGHEST of the following altitudes or flight levels FOR THE ROUTE SEGMENT

BEING FLOWN:

(1) The altitude or flight level assigned in the last ATC clearance received;

(2) The minimum altitude (converted, if appropriate, to minimum flight level as prescribed in 14 CFR

section 91.121(c)) for IFR operations; or

(3) The altitude or flight level ATC has advised may be expected in a further clearance.

Two-way Radio Communications Failure 6−4−1

AIM 2/20/25

NOTE−

The intent of the rule is that a pilot who has experienced two-way radio failure should select the appropriate altitude for

the particular route segment being flown and make the necessary altitude adjustments for subsequent route segments. If the

pilot received an “expect further clearance” containing a higher altitude to expect at a specified time or fix, maintain the

highest of the following altitudes until that time/fix:

(1) the last assigned altitude; or

(2) the minimum altitude/flight level for IFR operations.

Upon reaching the time/fix specified, the pilot should commence climbing to the altitude advised to expect. If the radio failure

occurs after the time/fix specified, the altitude to be expected is not applicable and the pilot should maintain an altitude

consistent with 1 or 2 above. If the pilot receives an “expect further clearance” containing a lower altitude, the pilot should

maintain the highest of 1 or 2 above until that time/fix specified in subparagraph (c) Leave clearance limit, below.

EXAMPLE−

1. A pilot experiencing two-way radio failure at an assigned altitude of 7,000 feet is cleared along a direct route which will

require a climb to a minimum IFR altitude of 9,000 feet, should climb to reach 9,000 feet at the time or place where it becomes

necessary (see 14 CFR section 91.177(b)). Later while proceeding along an airway with an MEA of 5,000 feet, the pilot

would descend to 7,000 feet (the last assigned altitude), because that altitude is higher than the MEA.

2. A pilot experiencing two-way radio failure while being progressively descended to lower altitudes to begin an approach

is assigned 2,700 feet until crossing the VOR and then cleared for the approach. The MOCA along the airway is 2,700 feet

and MEA is 4,000 feet. The aircraft is within 22 NM of the VOR. The pilot should remain at 2,700 feet until crossing the VOR

because that altitude is the minimum IFR altitude for the route segment being flown.

3. The MEA between a and b: 5,000 feet. The MEA between b and c: 5,000 feet. The MEA between c and d: 11,000 feet.

The MEA between d and e: 7,000 feet. A pilot had been cleared via a, b, c, d, to e. While flying between a and b the assigned

altitude was 6,000 feet and the pilot was told to expect a clearance to 8,000 feet at b. Prior to receiving the higher altitude

assignment, the pilot experienced two-way failure. The pilot would maintain 6,000 to b, then climb to 8,000 feet (the altitude

advised to expect). The pilot would maintain 8,000 feet, then climb to 11,000 at c, or prior to c if necessary to comply with

an MCA at c. (14 CFR section 91.177(b).) Upon reaching d, the pilot would descend to 8,000 feet (even though the MEA

was 7,000 feet), as 8,000 was the highest of the altitude situations stated in the rule (14 CFR section 91.185).

(1) When the clearance limit is a fix from which an approach begins, commence descent or descent and

approach as close as possible to the expect further clearance time if one has been received, or if one has not been

received, as close as possible to the Estimated Time of Arrival (ETA) as calculated from the filed or amended

(with ATC) Estimated Time En Route (ETE).

(2) If the clearance limit is not a fix from which an approach begins, leave the clearance limit at the

expect further clearance time if one has been received, or if none has been received, upon arrival over the

clearance limit, and proceed to a fix from which an approach begins and commence descent or descent and

approach as close as possible to the estimated time of arrival as calculated from the filed or amended (with ATC)

estimated time en route.

6−4−2. Transponder Operation During Two-way Communications Failure

a. If an aircraft with a coded radar beacon transponder experiences a loss of two-way radio capability, the pilot

should adjust the transponder to reply on Mode A/3, Code 7600.

b. The pilot should understand that the aircraft may not be in an area of radar coverage.

6−4−3. Reestablishing Radio Contact

a. In addition to monitoring the NA V AID voice feature, the pilot should attempt to reestablish

communications by attempting contact:

1. On the previously assigned frequency; or

6−4−2 Two-way Radio Communications Failure

2/20/25 AIM

2. With an FSS or with New York Radio or San Francisco Radio.

b. If communications are established with an FSS or New York Radio or San Francisco Radio, the pilot should

advise that radio communications on the previously assigned frequency have been lost giving the aircraft’s

position, altitude, last assigned frequency and then request further clearance from the controlling facility. The

preceding does not preclude the use of 121.5 MHz. There is no priority on which action should be attempted first.

If the capability exists, do all at the same time.

NOTE−

New York Radio and San Francisco Radio are operated by Collins Aerospace, Incorporated (formerly ARINC) under

contract with the F AA for communications services. These Radio facilities have the capability of relaying information

to/from ATC facilities throughout the country.

Two-way Radio Communications Failure 6−4−3

2/20/25 AIM

Section 5. Aircraft Rescue and

Fire Fighting Communications

6−5−1. Discrete Emergency Frequency

a. Direct contact between an emergency aircraft flight crew, Aircraft Rescue and Fire Fighting Incident

Commander (ARFF IC), and the Airport Traffic Control Tower (ATCT), is possible on an aeronautical radio

frequency (Discrete Emergency Frequency [DEF]), designated by Air Traffic Control (ATC) from the

operational frequencies assigned to that facility.

b. Emergency aircraft at airports without an ATCT, (or when the ATCT is closed), may contact the ARFF IC

(if ARFF service is provided), on the Common Traffic Advisory Frequency (CTAF) published for the airport

or the civil emergency frequency 121.5 MHz.

6−5−2. Radio Call Signs

Preferred radio call sign for the ARFF IC is “(location/facility) Command” when communicating with the flight

crew and the FAA ATCT.

EXAMPLE−

LAX Command.

Washington Command.

6−5−3. ARFF Emergency Hand Signals

In the event that electronic communications cannot be maintained between the ARFF IC and the flight crew,

standard emergency hand signals as depicted in FIG 6−5−1 through FIG 6−5−3 should be used. These hand

signals should be known and understood by all cockpit and cabin aircrew, and all ARFF firefighters.

FIG 6−5−1

Recommend Evacuation

Aircraft Rescue and Fire Fighting Communications 6−5−1

AIM 2/20/25

FIG 6−5−2

Recommend Stop

FIG 6−5−3

Emergency Contained

6−5−2 Aircraft Rescue and Fire Fighting Communications

2/20/25 AIM

Chapter 7. Safety of Flight

Section 1. Meteorology

7−1−1. National Weather Service Aviation Weather Service Program

a. Weather service to aviation is a joint effort of the National Oceanic and Atmospheric Administration

(NOAA), the National Weather Service (NWS), the Federal Aviation Administration (FAA), Department of

Defense, and various private sector aviation weather service providers. Requirements for all aviation weather

products originate from the FAA, which is the Meteorological Authority for the U.S.

b. NWS meteorologists are assigned to all air route traffic control centers (ARTCC) as part of the Center

Weather Service Units (CWSU) as well as the Air Traffic Control System Command Center (ATCSCC). These

meteorologists provide specialized briefings as well as tailored forecasts to support the needs of the FAA and

other users of the NAS.

c. Aviation Products

1. The NWS maintains an extensive surface, upper air, and radar weather observing program; and a

nationwide aviation weather forecasting service.

2. Airport observations (METAR and SPECI) supported by the NWS are provided by automated observing

systems.

3. Terminal Aerodrome Forecasts (TAF) are prepared by 123 NWS Weather Forecast Offices (WFOs) for

over 700 airports. These forecasts are valid for 24 or 30 hours and amended as required.

4. Inflight aviation advisories (for example, Significant Meteorological Information (SIGMETs) and

Airmen’s Meteorological Information (AIRMETs)) are issued by three NWS Meteorological Watch Offices

(MWOs); the Aviation Weather Center (AWC) in Kansas City, MO, the Alaska Aviation Weather Unit (AAWU)

in Anchorage, AK, and the Weather Service Forecast Office (WFO) in Honolulu, HI. The AWC, the AAWU,

and WSFO Honolulu issue area forecasts for selected areas. In addition, NWS meteorologists assigned to most

ARTCCs as part of the Center Weather Service Unit (CWSU) provide Center Weather Advisories (CWAs) and

gather weather information to support the needs of the FAA and other users of the system.

5. Several NWS National Centers for Environmental Production (NCEP) provide aviation specific weather

forecasts, or select public forecasts which are of interest to pilots and operators.

(a) The Aviation Weather Center (AWC) displays a variety of domestic and international aviation

forecast products over the Internet at aviationweather.gov.

(b) The NCEP Central Operations (NCO) is responsible for the operation of many numerical weather

prediction models, including those which produce the many wind and temperature aloft forecasts.

guidance forecasts.

(d) The National Hurricane Center (NHC) issues forecasts on tropical weather systems (for example,

hurricanes).

(e) The Space Weather Prediction Center (SWPC) provides alerts, watches, warnings and forecasts for

space weather events (for example, solar storms) affecting or expected to affect Earth’s environment.

(f) The Weather Prediction Center (WPC) provides analysis and forecast products on a national scale

including surface pressure and frontal analyses.

6. NOAA operates two V olcanic Ash Advisory Centers (V AAC) which issue forecasts of ash clouds

following a volcanic eruption in their area of responsibility.

Meteorology 7−1−1

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7. Details on the products provided by the above listed offices and centers is available in FAA−H−8083−28,

Aviation Weather Handbook.

d. Weather element values may be expressed by using different measurement systems depending on several

factors, such as whether the weather products will be used by the general public, aviation interests, international

services, or a combination of these users. FIG 7−1−1 provides conversion tables for the most used weather

elements that will be encountered by pilots.

7−1−2. FAA Weather Services

a. The FAA provides the Flight Service program, which serves the weather needs of pilots through its flight

service stations (FSS). Pilots may access weather information through www.1800wxbrief.com. To contact Flight

Service in the CONUS, Hawaii, and U.S. territories; call 1−800−WX−BRIEF (1−800−992−7433); in Alaska call

1−833−AK−BRIEF (1−833−252−7433).

b. The FAA maintains an extensive surface weather observing program. Airport observations (METAR and

SPECI) in the U.S. are provided by automated observing systems. Various levels of human oversight of the

METAR and SPECI reports and augmentation may be provided at select larger airports by either government

or contract personnel qualified to report specified weather elements that cannot be detected by the automated

observing system. The requirements to issue SPECI reports are detailed in TBL 7−1−1.

TBL 7−1−1

SPECI Issuance Table

1 Wind Shift Wind direction changes by 45° or more, in less than 15 minutes, and the wind speed is

10 kt or more throughout the wind shift.

2 Visibility

The surface visibility (as reported in the body of the report):

Decreases to less than 3 sm, 2 sm, 1 sm, ½ sm, ¼ sm or the lowest standard instrument

approach procedure (IAP) minimum.1

Increases to equal to or exceed 3 sm, 2 sm, 1 sm, ½ sm, ¼ sm or the lowest standard

IAP minimum.1

1 As published in the U.S. Terminal Procedures. If none published, use ½ sm.

3 RVR

The highest value from the designated RVR runway decreases to less than 2,400 ft during

the preceding 10 minutes; or, if the RVR is below 2,400 ft, increases to equal to or exceed

2,400 ft during the preceding 10 minutes. U.S. military stations may not report a SPECI

based on RVR.

Tornado, Funnel

Cloud, or

Waterspout

Is observed.

Disappears from sight or ends.

5 Thunderstorm

Begins (a SPECI is not required to report the beginning of a new thunderstorm if one

is currently reported).

Ends.

6 Precipitation

Hail begins or ends.

Freezing precipitation begins, ends, or changes intensity.

Ice pellets begin, end, or change intensity.

Snow begins, ends, or changes intensity.

7−1−2 Meteorology

AIM2/20/251/22/26 AIM

7 Squalls When a squall occurs. (Wind speed suddenly increases by at least 16 knots and is

sustained at 22 knots or more for at least one minute.)

8 Ceiling

The ceiling changes1 through:

3,000 ft.

1,500 ft.

1,000 ft.

500 ft.

The lowest standard IAP minimum.2

1 “Ceiling change” means that it forms, dissipates below, decreases to less than, or, if

below, increases to equal or exceed the values listed.

2 As published in the U.S. Terminal Procedures. If none published, use 200 ft.

9 Sky Condition A layer of clouds or obscurations aloft is present below 1,000 ft and no layer aloft was

reported below 1,000 ft in the preceding METAR or SPECI.

10 Volcanic

Eruption When an eruption is first noted.

11 Aircraft Mishap

Upon notification of an aircraft mishap, 1 unless there has been an intervening

observation.

1 “Aircraft mishap” is an inclusive term to denote the occurrence of an aircraft accident

or incident.

12 Miscellaneous Any other meteorological situation designated by the responsible agency of which, in

the opinion of the observer, is critical.

c. Other Sources of Weather Information

1. Weather and aeronautical information are available from numerous private industry sources on an

individual or contract pay basis. Prior to every flight, pilots should gather all information vital to the nature of

the flight. Pilots can receive a regulatory compliant briefing without contacting Flight Service. Pilots are

encouraged to use automated resources and review AC 91−92, Pilot’s Guide to a Preflight Briefing, for more

information.

2. Pilots can access Leidos Flight Services via the Internet at http://www.1800wxbrief.com. Pilots can

receive preflight weather data and file VFR and IFR flight plans.

7−1−3. Use of Aviation Weather Products

a. Air carriers and operators certificated under the provisions of 14 CFR part 119 are required to use the

aeronautical weather information systems defined in the Operations Specifications issued to that certificate

holder by the FAA. These systems may utilize basic FAA/National Weather Service (NWS) weather services,

contractor− or operator−proprietary weather services and/or Enhanced Weather Information System (EWINS)

when approved in the Operations Specifications. As an integral part of this system approval, the procedures for

collecting, producing and disseminating aeronautical weather information, as well as the crew member and

dispatcher training to support the use of system weather products, must be accepted or approved.

b. Operators not certificated under the provisions of 14 CFR part 119 are encouraged to use FAA/NWS

products through Flight Service Stations, Leidos Flight Service, and/or Flight Information Services−Broadcast

(FIS−B).

c. The suite of available aviation weather product types is expanding, with the development of new sensor

systems, algorithms and forecast models. The FAA and NWS, supported by various weather research

Meteorology 7−1−3

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laboratories and corporations under contract to the Government, develop and implement new aviation weather

product types. The FAA’s NextGen Aviation Weather Research Program (AWRP) facilitates collaboration

between the NWS, the FAA, and various industry and research representatives. This collaboration ensures that

user needs and technical readiness requirements are met before experimental products mature to operational

application.

d. The AWRP manages the transfer of aviation weather R&D to operational use through technical review

panels and conducting safety assessments to ensure that newly developed aviation weather products meet

regulatory requirements and enhance safety.

FIG 7−1−1

Weather Elements Conversion Tables

e. The AWRP review and decision−making process applies criteria to weather products at various stages . The

stages are composed of the following:

7−1−4 Meteorology

AIM2/20/251/22/26 AIM

1. Sponsorship of user needs.

2. R & D and controlled testing.

3. Experimental application.

4. Operational application.

f. Pilots and operators should be aware that weather services provided by entities other than FAA, NWS, or

their contractors may not meet FAA/NWS quality control standards. Hence, operators and pilots contemplating

using such services should request and/or review an appropriate description of services and provider disclosure.

This should include, but is not limited to, the type of weather product (for example, current weather or forecast

weather), the currency of the product (that is, product issue and valid times), and the relevance of the product.

Pilots and operators should be cautious when using unfamiliar products, or products not supported by FAA/NWS

technical specifications.

NOTE−

When in doubt, consult with a F AA Flight Service Station Specialist.

g. In addition, pilots and operators should be aware there are weather services and products available from

government organizations beyond the scope of the AWRP process mentioned earlier in this section. For example,

governmental agencies such as the NWS and the Aviation Weather Center (AWC), or research organizations such

as the National Center for Atmospheric Research (NCAR) display weather “model data” and “experimental”

products which require training and/or expertise to properly interpret and use. These products are developmental

prototypes that are subject to ongoing research and can change without notice. Therefore, some data on display

by government organizations, or government data on display by independent organizations may be unsuitable

for flight planning purposes. Operators and pilots contemplating using such services should request and/or

review an appropriate description of services and provider disclosure. This should include, but is not limited to,

the type of weather product (for example, current weather or forecast weather), the currency of the product (i.e.,

product issue and valid times), and the relevance of the product. Pilots and operators should be cautious when

using unfamiliar weather products.

NOTE−

When in doubt, consult with a F AA Flight Service Station Specialist.

h. With increased access to weather products via the public Internet, the aviation community has access to

an overwhelming amount of weather information and data that support self −briefing. the Aviation Weather

Handbook, FAA−H−8083−28 (current edition), describes the weather products distributed by the NWS. Pilots

and operators using the public Internet to access weather from a third party vendor should request and/or review

an appropriate description of services and provider disclosure. This should include, but is not limited to, the type

of weather product (for example, current weather or forecast weather), the currency of the product (i.e., product

issue and valid times), and the relevance of the product. Pilots and operators should be cautious when using

unfamiliar weather products and when in doubt, consult with a Flight Service Specialist.

i. The development of new weather products, coupled with the termination of some legacy textual and

graphical products may create confusion between regulatory requirements and the new products. All

flight−related, aviation weather decisions must be based on all available pertinent weather products. As every

flight is unique and the weather conditions for that flight vary hour by hour, day to day, multiple weather products

may be necessary to meet aviation weather regulatory requirements. Many new weather products now have a

Precautionary Use Statement that details the proper use or application of the specific product.

j. The FAA has identified three distinct types of weather information available to pilots and operators.

1. Observations. Raw weather data collected by some type of sensor suite including surface and airborne

observations, radar, lightning, satellite imagery, and profilers.

2. Analysis. Enhanced depiction and/or interpretation of observed weather data.

3. Forecasts . Predictions of the development and/or movement of weather phenomena based on

meteorological observations and various mathematical models.

Meteorology 7−1−5

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k. Not all sources of aviation weather information are able to provide all three types of weather information.

The FAA has determined that operators and pilots may utilize the following approved sources of aviation weather

information:

1. Federal Government. The FAA and NWS collect raw weather data, analyze the observations, and

produce forecasts. The FAA and NWS disseminate meteorological observations, analyses, and forecasts through

a variety of systems. In addition, the Federal Government is the only approval authority for sources of weather

observations; for example, contract towers and airport operators may be approved by the Federal Government

to provide weather observations.

2. Enhanced Weather Information System (EWINS). An EWINS is an FAA authorized, proprietary

system for tracking, evaluating, reporting, and forecasting the presence or lack of adverse weather phenomena.

The FAA authorizes a certificate holder to use an EWINS to produce flight movement forecasts, adverse weather

phenomena forecasts, and other meteorological advisories. For more detailed information regarding EWINS, see

FAA−H−8083−28, Aviation Weather Handbook, and the Flight Standards Information Management System

8900.1.

3. Commercial Weather Information Providers. In general, commercial providers produce proprietary

weather products based on NWS/FAA products with formatting and layout modifications but no material

changes to the weather information itself. This is also referred to as “repackaging.” In addition, commercial

providers may produce analyses, forecasts, and other proprietary weather products that substantially alter the

information contained in government−produced products. However, those proprietary weather products that

substantially alter government−produced weather products or information, may only be approved for use by 14

CFR part 121 and part 135 certificate holders if the commercial provider is EWINS qualified.

NOTE−

Commercial weather information providers contracted by F AA to provide weather observations, analyses, and forecasts

(e.g., contract towers) are included in the Federal Government category of approved sources by virtue of maintaining

required technical and quality assurance standards under Federal Government oversight.

7−1−4. Graphical Forecasts for Aviation (GFA)

a. The GFA website is intended to provide the necessary aviation weather information to give users a complete

picture of the weather that may affect flight in the continental United States (CONUS). The website includes

observational data, forecasts, and warnings that can be viewed from 14 hours in the past to 15 hours in the future,

including thunderstorms, clouds, flight category, precipitation, icing, turbulence, and wind. Hourly model data

and forecasts, including information on clouds, flight category, precipitation, icing, turbulence, wind, and

graphical output from the National Weather Service’s (NWS) National Digital Forecast Data (NDFD) are

available. Wind, icing, and turbulence forecasts are available in 3,000 ft increments from the surface up to 30,000

ft MSL, and in 6,000 ft increments from 30,000 ft MSL to 48,000 ft MSL. Turbulence forecasts are also broken

into low (below 18,000 ft MSL) and high (at or above 18,000 ft MSL) graphics. A maximum icing graphic and

maximum wind velocity graphic (regardless of altitude) are also available. Built with modern geospatial

information tools, users can pan and zoom to focus on areas of greatest interest. Target users are commercial and

general aviation pilots, operators, briefers, and dispatchers.

b. Weather Products.

1. The Aviation Forecasts include gridded displays of various weather parameters as well as NWS textual

weather observations, forecasts, and warnings. Ici ng, turbulence, and wind gridded products are

three−dimensional. Other gridded products are two −dimensional and may represent a “composite” of a

three−dimensional weather phenomenon or a surface weather variable, such as horizontal visibility. The

following are examples of aviation forecasts depicted on the GFA:

(a) Terminal Aerodrome Forecast (TAF)

(b) Ceiling & Visibility (CIG/VIS)

7−1−6 Meteorology

2/20/25 AIM

(d) Precipitation / Weather (PCPN/WX)

(e) Thunderstorm (TS)

(f) Winds

(g) Turbulence

(h) Ice

2. Observations & Warnings (Obs/Warn). The Obs/Warn option provides an option to display weather

data for the current time and the previous 14 hours (rounded to the nearest hour). Users may advance through

time using the arrow buttons or by clicking on the desired hour. Provided below are the Obs/Warn product tabs

available on the GFA website:

(a) METAR

(b) Precipitation/Weather (PCPN/WX)

(d) Pilot Weather Report (PIREP)

(e) Radar & Satellite (RAD/SAT)

3. The GFA will be continuously updated and available online at http://aviationweather.gov/gfa. Upon

clicking the link above, select INFO on the top right corner of the map display. The next screen presents the option

of selecting Overview, Products, and Tutorial. Simply select the tab of interest to explore the enhanced digital

and graphical weather products designed to replace the legacy FA. Users should also refer to the Aviation Weather

Handbook, FAA−H−8083−28, Graphical Forecasts for Aviation (GFA) Tool, for more detailed information on

the GFA.

4. GFA Static Images. Some users with limited internet connectivity may access static images via the

Aviation Weather Center (AWC) Decision Support Imagery at: https://aviationweather.gov/graphics/. There are

two static graphical images available, titled Aviation Cloud Forecast and Aviation Surface Forecast. The

Aviation Cloud Forecast provides cloud coverage, bases, layers, and tops with AIRMETs for mountain

obscuration and AIRMETs for icing overlaid. The Aviation Surface Fo recast provides visibility, weather

phenomena, and winds (including wind gusts) with AIRMETs for instrument flight rules conditions and

AIRMETs for sustained surface winds of 30 knots or more overlaid. These images are presented on ten separate

maps providing forecast views for the entire contiguous United States (U.S.) on one and nine regional views

which provide more detail for the user. They are updated every 3 hours and provide forecast snapshots for 3, 6,

9, 12, 15, and 18 hours into the future. (See FIG 7−1−2 and FIG 7−1−3.)

NOTE−

The contiguous United States (U.S.) refers to the 48 adjoining U.S. states on the continent of North America that are south

of Canada and north of Mexico, plus the District of Columbia. The term excludes the states of Alaska and Hawaii, and all

off−shore U.S. territories and possessions, such as Puerto Rico.

Meteorology 7−1−7

AIM 2/20/25

FIG 7−1−2

Aviation Surface Forecast

FIG 7−1−3

Aviation Cloud Forecast

7−1−5. Preflight Briefing

a. Flight Service is one of the primary sources for obtaining preflight briefings and to file flight plans by phone

or the Internet. Flight Service Specialists are qualified and certificated as Pilot Weather Briefers by the FAA.

7−1−8 Meteorology

2/20/25 AIM

They are not authorized to make original forecasts, but are authorized to translate and interpret available forecasts

and reports directly into terms describing the weather conditions which you can expect along your flight route

and at your destination. Prior to every flight, pilots should gather all information vital to the nature of the flight.

Pilots can receive a regulatory compliant briefing without contacting Flight Service. Pilots are encouraged to use

automated resources and review AC 91−92, Pilot’s Guide to a Preflight Briefing, for more information. Pilots

who prefer to contact Flight Service are encouraged to conduct a self −brief prior to calling. Conducting a

self−brief before contacting Flight Service provides familiarity of meteorological and aeronautical conditions

applicable to the route of flight and promotes a better understanding of weather information. Three basic types

of preflight briefings (Standard, Abbreviated, and Outlook) are available to serve the pilot’s specific needs. Pilots

should specify to the briefer the type of briefing they want, along with their appropriate background information.

This will enable the briefer to tailor the information to the pilot’s intended flight. The following paragraphs

describe the types of briefings available and the information provided in each briefing.

REFERENCE−

AIM, Para 5−1−1, Preflight Preparation, for items that are required.

b. Standard Briefing. You should request a Standard Briefing any time you are planning a flight and you

have not received a previous briefing or have not received preliminary information through online resources.

International data may be inaccurate or incomplete. If you are planning a flight outside of U.S. controlled

airspace, the briefer will advise you to check data as soon as practical after entering foreign airspace, unless you

advise that you have the international cautionary advisory. The briefer will automatically provide the following

information in the sequence listed, except as noted, when it is applicable to your proposed flight.

1. Adverse Conditions. Significant meteorological and/or aeronautical information that might influence

the pilot to alter or cancel the proposed flight; for example, hazardous weather conditions, airport closures, air

traffic delays, etc. Pilots should be especially alert for current or forecast weather that could reduce flight

minimums below VFR or IFR conditions. Pilots should also be alert for any reported or forecast icing if the

aircraft is not certified for operating in icing conditions. Flying into areas of icing or weather below minimums

could have disastrous results.

2. VFR Flight Not Recommended. When VFR flight is proposed and sky conditions or visibilities are

present or forecast, surface or aloft, that, in the briefer’s judgment, would make flight under VFR doubtful, the

briefer will describe the conditions, describe the affected locations, and use the phrase “VFR flight not

recommended.” This recommendation is advisory in nature. The final decision as to whether the flight can be

conducted safely rests solely with the pilot. Upon receiving a “ VFR flight not recommended ” statement, the

non−IFR rated pilot will need to make a “go or no go” decision. This decision should be based on weighing the

current and forecast weather conditions against the pilot’s experience and ratings. The aircraft’s equipment,

capabilities and limitations should also be considered.

NOTE−

Pilots flying into areas of minimal VFR weather could encounter unforecasted lowering conditions that place the aircraft

outside the pilot’ s ratings and experience level. This could result in spatial disorientation and/or loss of control of the

aircraft.

3. Synopsis. A brief statement describing the type, location and movement of weather systems and/or air

masses which might affect the proposed flight.

NOTE−

These first 3 elements of a briefing may be combined in any order when the briefer believes it will help to more clearly

describe conditions.

4. Current Conditions. Reported weather conditions applicable to the flight will be summarized from all

available sources; e.g., METARs/ SPECIs, PIREPs, RAREPs. This element will be omitted if the proposed time

of departure is beyond 2 hours, unless the information is specifically requested by the pilot.

5. En Route Forecast. Forecast en route conditions for the proposed route are summarized in logical

order; i.e., departure/climbout, en route, and descent. (Heights are MSL, unless the contractions “AGL” or “CIG”

are denoted indicating that heights are above ground.)

Meteorology 7−1−9

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6. Destination Forecast. The destination forecast for the planned ETA. Any significant changes within

1 hour before and after the planned arrival are included.

7. Winds Aloft. Forecast winds aloft will be provided in knots and degrees, referenced to true north. The

briefer will interpolate wind directions and speeds between levels and stations as necessary to provide expected

conditions at planned altitudes. (Heights are MSL.) Temperature information will be provided on request.

8. Notices to Airmen (NOTAMs).

(a) Available NOTAM (D) information pertinent to the proposed flight, including special use airspace

(SUA) NOTAMs for restricted areas, aerial refueling, and night vision goggles (NVG).

NOTE−

Other SUA NOTAMs (D), such as military operations area (MOA), military training route (MTR), and warning area

NOTAMs, are considered “upon request” briefing items as indicated in paragraph 7−1−4b10(a).

(b) Prohibited Areas P−40, P−49, P−56, and the special flight rules area (SFRA) for Washington, DC.

unless specifically asked. Pilots authorized by the FAA to use special instrument approach procedures must

specifically request FDC NOTAM information for these procedures.

NOTE−

1. NOTAM information may be combined with current conditions when the briefer believes it is logical to do so.

2. Airway NOTAMs, procedural NOTAMs, and NOTAMs that are general in nature and not tied to a specific airport/facility

(for example, flight advisories and restrictions, open duration special security instructions, and special flight rules areas)

are briefed solely by pilot request. For complete flight information, pilots are urged to review the Domestic Notices and

International Notices found in the External Links section of the Federal NOTAM System (FNS) NOTAM Search System and

the Chart Supplement in addition to obtaining a briefing.

9. ATC Delays. Any known ATC delays and flow control advisories which might affect the proposed

flight.

10. Pilots may obtain the following from flight service station briefers upon request:

(a) Information on SUA and SUA−related airspace, except those listed in paragraph 7−1−4b8.

NOTE−

1. For the purpose of this paragraph, SUA and related airspace includes the following types of airspace: alert area, military

operations area (MOA), warning area, and air traffic control assigned airspace (ATCAA). MTR data includes the following

types of airspace: IFR training routes (IR), VFR training routes (VR), and slow training routes (SR).

2. Pilots are encouraged to request updated information from ATC facilities while in flight.

(b) A review of airway NOTAMs, procedural NOTAMs, and NOTAMs that are general in nature and not

tied to a specific airport/facility (for example, flight advisories and restrictions, open duration special security

instructions, and special flight rules areas), Domestic Notices and International Notices. Domestic Notices and

International Notices are found in the External Links section of the Federal NOTAM System (FNS) NOTAM

Search System.

(d) Information regarding such items as air traffic services and rules, customs/immigration procedures,

ADIZ rules, search and rescue, etc.

(e) GPS RAIM availability for 1 hour before to 1 hour after ETA or a time specified by the pilot.

(f) Other assistance as required.

c. Abbreviated Briefing. Request an Abbreviated Briefing when you need information to supplement mass

disseminated data, update a previous briefing, or when you need only one or two specific items. Provide the

briefer with appropriate background information, the time you received the previous information, and/or the

specific items needed. You should indicate the source of the information already received so that the briefer can

7−1−10 Meteorology

AIM2/20/258/7/25 AIM

limit the briefing to the information that you have not received, and/or appreciable changes in

meteorological/aeronautical conditions since your previous briefing. To the extent possible, the briefer will

provide the information in the sequence shown for a Standard Briefing. If you request only one or two specific

items, the briefer will advise you if adverse conditions are present or forecast. (Adverse conditions contain both

meteorological and/or aeronautical information.) Details on these conditions will be provided at your request.

International data may be inaccurate or incomplete. If you are planning a flight outside of U.S. controlled

airspace, the briefer will advise you to check data as soon as practical after entering foreign airspace, unless you

advise that you have the international cautionary advisory.

d. Outlook Briefing. You should request an Outlook Briefing whenever your proposed time of departure is

six or more hours from the time of the briefing. The briefer will provide available forecast data applicable to the

proposed flight. This type of briefing is provided for planning purposes only. You should obtain a Standard or

Abbreviated Briefing prior to departure in order to obtain such items as adverse conditions, current conditions,

updated forecasts, winds aloft and NOTAMs, etc.

e. When filing a flight plan only, you will be asked if you require the latest information on adverse conditions

pertinent to the route of flight.

f. Inflight Briefing. You are encouraged to conduct a self −briefing using online resources or obtain your

preflight briefing by telephone or in person (Alaska only) before departure. In those cases where you need to

obtain a preflight briefing or an update to a previous briefing by radio, you should contact the nearest FSS to

obtain this information. After communications have been established, advise the specialist of the type briefing

you require and provide appropriate background information. You will be provided information as specified in

the above paragraphs, depending on the type of briefing requested. En Route advisories tailored to the phase of

flight that begins after climb−out and ends with descent to land are provided upon pilot request. Besides Flight

Service, there are other resources available to the pilot in flight, including:

Automatic Dependent Surveillance −Broadcast (ADS −B). Free traffic, weather, and flight information are

available on ADS−B In receivers that can receive data over 978 MHz (UAT) broadcasts. These services are

available across the nation to aircraft owners who equip with ADS−B In, with further advances coming from

airborne and runway traffic awareness. Even search −and−rescue operations benefit from accurate ADS −B

tracking.

Flight Information Services−Broadcast (FIS−B). FIS−B is a free service; but is only available to aircraft that can

receive data over 978 MHz (UA T). FIS−B automatically transmits a wide range of weather products with national

and regional focus to all equipped aircraft. Having current weather and aeronautical information in the cockpit

helps pilots plan more safe and efficient flight paths, as well as make strategic decisions during flight to avoid

potentially hazardous weather.

Pilots are encouraged to provide a continuous exchange of information on weather, winds, turbulence, flight

visibility, icing, etc., between pilots and inflight specialists. Pilots should report good weather as well as bad, and

confirm expected conditions as well as unexpected. Remember that weather conditions can change rapidly and

that a “go or no go” decision, as mentioned in paragraph 7−1−4b2, should be assessed at all phases of flight.

g. Following any briefing, feel free to ask for any information that you or the briefer may have missed or are

not understood. This way, the briefer is able to present the information in a logical sequence, and lessens the

chance of important items being overlooked.

7−1−6. Inflight Aviation Weather Advisories

a. Inflight Aviation Weather Advisories are forecasts to advise en route aircraft of development of potentially

hazardous weather. Inflight aviation weather advisories in the conterminous U.S. are issued by the Aviation

Weather Center (AWC) in Kansas City, MO, as well as 20 Center Weather Service Units (CWSU) associated with

ARTCCs. AWC also issues advisories for portions of the Gulf of America, Atlantic and Pacific Oceans, which

Meteorology 7−1−11

AIM 2/20/25

are under the control of ARTCCs with Oceanic flight information regions (FIRs). The Weather Forecast Office

(WFO) in Honolulu issues advisories for the Hawaiian Islands and a large portion of the Pacific Ocean. In Alaska,

the Alaska Aviation Weather Unit (AAWU) issues inflight aviation weather advisories along with the Anchorage

CWSU. All heights are referenced MSL, except in the case of ceilings (CIG) which indicate AGL.

b. There are four types of inflight aviation weather advisories: the SIGMET, the Convective SIGMET, the

AIRMET, and the Center Weather Advisory (CWA). All of these advisories use VORs, airports, or well−known

geographic areas to describe the hazardous weather areas.

c. The Severe Weather Watch Bulletins (WWs), (with associated Alert Messages) (AWW) supplements these

Inflight Aviation Weather Advisories.

d. SIGMET. A SIGMET is a concise description of the occurrence or expected occurrence of specified en

route weather phenomena which is expected to affect the safety of aircraft operations.

1. SIGMETs:

(a) Are intended for dissemination to all pilots in flight to enhance safety.

(b) Are issued by the responsible MWO as soon as it is practical to alert operators and aircrews of

hazardous en route conditions.

cyclones and volcanic ash clouds are valid for 6 hours. Unscheduled updates and corrections are issued as

necessary.

(d) Use geographical points to describe the hazardous weather areas. These points can reference either

VORs, airports, or latitude−longitude, depending on SIGMET location. If the total area to be affected during the

forecast period is very large, it could be that, in actuality, only a small portion of this total area would be affected

at any one time.

EXAMPLE−

Example of a SIGMET:

BOSR WS 050600

SIGMET ROMEO 2 VALID UNTIL 051000

ME NH VT

FROM CAR TO YSJ TO CON TO MPV TO CAR

OCNL SEV TURB BLW 080 EXP DUE TO STG NWLY FLOW. CONDS CONTG BYD 1000Z.

2. SIGMETs over the contiguous U.S.:

(a) Are issued corresponding to the areas described in FIG 7−1−5. and are only for non−convective

weather. The U.S. issues a special category of SIGMETs for convective weather called Convective SIGMETs.

(b) Are identified by an alphabetic designator from November through Yankee, excluding Sierra and

Tango. Issuance for the same phenomenon will be sequentially numbered, using the original designator until the

phenomenon ends. For example, the first issuance in the Chicago (CHI) area (reference FIG 7−1−5) for

phenomenon moving from the Salt Lake City (SLC) area will be SIGMET Papa 3, if the previous two issuances,

Papa 1 and Papa 2, had been in the SLC area. Note that no two different phenomena across the country can have

the same alphabetic designator at the same time.

(d) Are issued when the following phenomena occur or are expected to occur:

(1) Severe icing not associated with thunderstorms.

(2) Severe or extreme turbulence or clear air turbulence (CAT) not associated with thunderstorms.

(3) Widespread dust storms or sandstorms lowering surface visibilities to below 3 miles.

(4) V olcanic ash.

7−1−12 Meteorology

2/20/25 AIM

3. SIGMETs over Alaska:

(a) Are issued for the Anchorage FIR including Alaska and nearby coastal waters corresponding to the

areas described in FIG 7−1−4. and are only for non−convective weather. The U.S. issues a special category of

SIGMETs for convective weather called Convective SIGMETs.

(b) Use location identifiers (either VORs or airports) to describe the hazardous weather areas.

(d) Are identified by an alphabetic designator from India through Mike.

(e) In addition to the phenomenon applicable to SIGMETs over the contiguous U.S., SIGMETs over

Alaska are also issued for:

(1) Tornadoes.

(2) Lines of thunderstorms.

(3) Embedded thunderstorms.

(4) Hail greater than or equal to ¾ inch in diameter.

FIG 7−1−4

Alaska SIGMET and Area Forecast Zones

4. SIGMETs over oceanic regions (New York Oceanic FIR, Oakland Oceanic FIR including Hawaii,

Houston Oceanic FIR, Miami Oceanic FIR, San Juan FIR), points of latitude and longitude are used to describe

the hazard area.

(a) SIGMETs over the Oakland Oceanic FIR west of 140 west and south of 30 north (including the

Hawaiian Islands) are identified by an alphabetic designator from November through Zulu.

Meteorology 7−1−13

AIM 2/20/253/15/077110.65R CHG 2AIM 7/9/26

(b) SIGMETs over the Oakland Oceanic FIR east of 140 west and north of 30 north are identified by an

alphabetic designator from Alpha through Mike.

FIR are identified by an alphabetic designator from Alpha through Mike.

(d) In addition to SIGMETs issued for the phenomenon for the contiguous U.S., SIGMETs in the oceanic

regions are also issued for:

(1) Tornadoes.

(2) Lines of thunderstorms.

(3) Embedded thunderstorms.

(4) Hail greater than or equal to ¾ inch in diameter.

e. Convective SIGMET

1. Convective SIGMETs are issued in the conterminous U.S. for any of the following:

(a) Severe thunderstorm due to:

(1) Surface winds greater than or equal to 50 knots.

(2) Hail at the surface greater than or equal to 3/4 inches in diameter.

(3) Tornadoes.

(b) Embedded thunderstorms.

(d) Thunderstorms producing precipitation greater than or equal to heavy precipitation affecting 40

percent or more of an area at least 3,000 square miles.

2. Any convective SIGMET implies severe or greater turbulence, severe icing, and low−level wind shear.

A convective SIGMET may be issued for any convective situation that the forecaster feels is hazardous to all

categories of aircraft.

3. Convective SIGMET bulletins are issued for the western (W), central (C), and eastern (E) United States.

(Convective SIGMETs are not issued for Alaska or Hawaii.) The areas are separated at 87 and 107 degrees west

longitude with sufficient overlap to cover most cases when the phenomenon crosses the boundaries. Bulletins

are issued hourly at H+55. Special bulletins are issued at any time as required and updated at H+55. If no criteria

meeting convective SIGMET requirements are obse rved or forecasted, the message “CONVECTIVE

SIGMET... NONE” will be issued for each area at H+55. Individual convective SIGMETs for each area (W, C,

E) are numbered sequentially from number one each day, beginning at 00Z. A convective SIGMET for a

continuing phenomenon will be reissued every hour at H+55 with a new number. The text of the bulletin consists

of either an observation and a forecast or just a forecast. The forecast is valid for up to 1 hour.

EXAMPLE−

CONVECTIVE SIGMET 44C

VALID UNTIL 1455Z

AR TX OK

FROM 40NE ADM-40ESE MLC-10W TXK-50WNW LFK-40ENE SJT-40NE ADM

AREA TS MOV FROM 26025KT. TOPS ABV FL450.

7−1−14 Meteorology

2/20/25 AIM

FIG 7−1−5

SIGMET Locations – Contiguous U.S.

FIG 7−1−6

Hawaii Area Forecast Locations

f. AIRMET. AIRMETs are a concise description of the occurrence or expected occurrence of specified en

route weather phenomena that may affect the safety of aircraft operations, but at intensities lower than those

which require the issuance of a SIGMET.

Meteorology 7−1−15

AIM 2/20/253/15/077110.65R CHG 2AIM 8/7/25

1. AIRMETs contain details about IFR conditions, extensive mountain obscuration, turbulence, strong

surface winds, icing, and freezing levels. Unscheduled updates and corrections are issued as necessary.

2. AIRMETs:

(a) Are intended to inform all pilots, but especially Visual Flight Rules pilots and operators of sensitive

aircraft, of potentially hazardous weather phenomena.

(b) Are issued on a scheduled basis every 6 hours, except every 8 hours in Alaska. Unscheduled updates

and corrections are issued as necessary.

safety. En route AIRMETs are available over flight service frequencies. Over the contiguous U.S., AIRMETs

are also available on equipment intended to display weather and other non −air traffic control−related flight

information to pilots using the Flight Information Service–Broadcast (FIS−B). In Alaska and Hawaii, AIRMETs

are broadcast on air traffic frequencies.

(d) Are issued for the contiguous U.S., Alaska, and Hawaii. No AIRMETs are issued for U.S. Oceanic

FIRs in the Gulf of America, Caribbean, Western Atlantic, and Pacific Oceans.

TBL 7−1−2

U. S. AIRMET Issuance Time and Frequency

Product Type Issuance Time Issuance Frequency

AIRMETs over the Contiguous U.S. 0245, 0845, 1445, 2045 UTC Every 6 hours

AIRMETs over Alaska

0515, 1315, 2115 UTC

(standard time)

0415, 1215, 2015 UTC

(Daylight savings time)

Every 8 hours

AIRMETs over Hawaii 0400, 1000, 1600, 2200 UTC Every 6 hours

3. AIRMETs over the Contiguous U.S.:

(a) Are displayed graphically on websites, such as, aviationweather.gov and 1800wxbrief.com, and

equipment receiving FIS−B information.

(b) Provide a higher forecast resolution than AIRMETs issued in text format.

(for example, 00, 03, 06, 09, and 12 hours). Additional forecasts may be inserted during the first 6 hours (for

example; 01, 02, 04, and 05). 00−hour represents the initial conditions, and the subsequent graphics depict the

area affected by the particular hazard at that valid time. Forecasts valid at 00 through 06 hours correspond to the

text AIRMET bulletin.

(d) Depict the following en route aviation weather hazards:

(1) Instrument flight rule conditions (ceiling < 1000’ and/or surface visibility < 3 miles).

(2) Widespread mountain obscuration.

(3) Moderate icing.

(4) Freezing levels.

(5) Moderate turbulence.

(6) Non−convective low−level wind shear potential below 2,000 feet AGL.

(7) Sustained surface winds greater than 30 knots.

7−1−16 Meteorology

2/20/25 AIM

4. Interpolation of time periods between AIRMETs over the contiguous U.S. valid times: Users must keep

in mind when using the AIRMET over the contiguous U.S. that if a 00 −hour forecast shows no significant

weather and a 03−hour forecast shows hazardous weather, they must assume a change is occurring during the

period between the two forecasts. It should be taken into consideration that the hazardous weather starts

immediately after the 00−hour forecast unless there is a defined initiation or ending time for the hazardous

weather. The same would apply after the 03 −hour forecast. The user should assume the hazardous weather

condition is occurring between the snap shots unless informed otherwise. For example, if a 00 −hour forecast

shows no hazard, a 03−hour forecast shows the presence of hazardous weather, and a 06−hour forecast shows

no hazard, the user should assume the hazard exists from the 0001 hour to the 0559 hour time period.

Meteorology 7−1−17

AIM 2/20/25

FIG 7−1−7

AIRMET over the Contiguous U.S.

7−1−18 Meteorology

2/20/25 AIM

5. AIRMETs over Alaska and Hawaii:

(a) AIRMETs over Alaska and Hawaii are in text format. The hazard areas are described using

well−known geographical areas. AIRMETs over Alaska are issued for three Alaskan regions corresponding to

Alaska area forecasts (See FIG 7−1−4).

(b) AIRMETs over Alaska are valid up to eight hours. AIRMETs over Hawaii are valid up to six hours.

Unscheduled issuances contain an update number for easier identification.

EXAMPLE−

Example of AIRMET Sierra issued for the Southeast Alaska area:

WAAK47 P AWU 241324

WA7O

JNUS WA 241315

AIRMET SIERRA FOR IFR AND MT OBSC VALID UNTIL 242115

LYNN CANAL AND GLACIER BAY JB

MTS OBSC BY CLDS/ISOL PCPN. NC.

CNTRL SE AK JC

MTS OCNL OBSC IN CLDS. NC.

SRN SE AK JD

PAWG−P AKT LN W OCNL CIGS BLW 010/VIS BLW 3SM BR. IMPR.

ERN GLF CST JE

OCNL CIGS BLW 010/VIS BLW 3SM BR/−RA BR. DTRT.

=JNUT WA 241315

AIRMET TANGO FOR TURB/STG SFC WINDS VALID UNTIL 242115

ERN GLF CST JE

OFSHR ICY BAY W SUSTAINED SFC WND 30 KTS

OR GTR. SPRDG E. INTSF .

=JNUZ WA 241315

AIRMET ZULU FOR ICING VALID UNTIL 242115

ERN GLF CST JE

16Z TO 19Z ALG CST W ICY BAY OCNL MOD ICEIC 080−160.

FZLVL 045 EXC 015 INLAND. WKN.

EXAMPLE−

Example of AIRMET Tango issued for Hawaii F A area:

WAHW31 PHFO 241529

WA0HI

HNLS WA 241600

AIRMET SIERRA UPDATE 2 FOR IFR VALID UNTIL 242200

NO SIGNIFICANT IFR EXP .

=HNLT WA 241600

AIRMET TANGO UPDATE 3 FOR TURB VALID UNTIL 242200

Meteorology 7−1−19

AIM 2/20/25

AIRMET TURB...HI

OVER AMD IMT S THRU W OF MTN.

TEMPO MOD TURB BLW 070.

COND CONT BEYOND 2200Z.

=HNLZ WA 241600

AIRMET ZULU UPDATE 2 FOR ICE AND FZLVL VALID UNTIL 242200

NO SIGNIFICANT ICE EXP

g. Watch Notification Messages

The Storm Prediction Center (SPC) in Norman, OK, issues Watch Notification Messages to provide an area threat

alert for forecast organized severe thunderstorms that may produce tornadoes, large hail, and/or convective

damaging winds within the CONUS. SPC issues three types of watch notification messages: Aviation Watch

Notification Messages, Public Severe Thunderstorm Watch Notification Messages, and Public Tornado Watch

Notification Messages.

It is important to note the difference between a Severe T hunderstorm (or Tornado) Watch and a Severe

Thunderstorm (or Tornado) Warning. A watch means severe weather is possible during the next few hours, while

a warning means that severe weather has been observed, or is expected within the hour. Only the SPC issues

Severe Thunderstorm and Tornado Watches, while only NWS Weather Forecasts Offices issue Severe

Thunderstorm and Tornado Warnings.

1. The Aviation Watch Notification Message. The Aviation Watch Notification Message product is an

approximation of the area of the Public Severe Thunderstorm Watch or Public Tornado Watch. The area may be

defined as a rectangle or parallelogram using VOR navigational aides as coordinates.

The Aviation Watch Notification Message was formerly known as the Alert Severe Weather Watch Bulletin

(AWW). The NWS no longer uses that title or acronym for this product. The NWS uses the acronym SAW for

the Aviation Watch Notification Message, but retains AWW in the product header for processing by weather data

systems.

EXAMPLE−

Example of an Aviation Watch Notification Message:

WWUS30 KWNS 271559

SAW2

SPC AWW 271559

WW 568 TORNADO AR LA MS 271605Z - 280000Z

AXIS..65 STATUTE MILES EAST AND WEST OF LINE..

45ESE HEZ/NATCHEZ MS/ - 50N TUP/TUPELO MS/

..AVIATION COORDS.. 55NM E/W /18WNW MCB - 60E MEM/

HAIL SURF ACE AND ALOFT..3 INCHES. WIND GUSTS..70 KNOTS. MAX TOPS TO 550. MEAN STORM MOTION

VECTOR 26030.

LAT...LON 31369169 34998991 34998762 31368948

THIS IS AN APPROXIMATION TO THE WATCH AREA. FOR A COMPLETE DEPICTION OF THE WATCH SEE

WOUS64 KWNS FOR WOU2.

2. Public Severe Thunderstorm Watch Notification Messages describe areas of expected severe

thunderstorms. (Severe thunderstorm criteria are 1-inch hail or larger and/or wind gusts of 50 knots [58 mph]

or greater). A Public Severe Thunderstorm Watch Notification Message contains the area description and axis,

the watch expiration time, a description of hail size and thunderstorm wind gusts expected, the definition of the

watch, a call to action statement, a list of other valid watches, a brief discussion of meteorological reasoning and

technical information for the aviation community.

3. Public Tornado Watch Notification Messages describe areas where the threat of tornadoes exists. A

Public Tornado Watch Notification Message contains the area description and axis, watch expiration time, the

term “damaging tornadoes,” a description of the largest hail size and strongest thunderstorm wind gusts expected,

the definition of the watch, a call to action statement, a list of other valid watches, a brief discussion of

7−1−20 Meteorology

2/20/25 AIM

meteorological reasoning and technical information for the aviation community. SPC may enhance a Public

Tornado Watch Notification Message by using the words “THIS IS A PARTICULARLY DANGEROUS

SITUATION” when there is a likelihood of multiple strong (damage of EF2 or EF3) or violent (damage of EF4

or EF5) tornadoes.

4. Public severe thunderstorm and tornado watch notification messages were formerly known as the Severe

Weather Watch Bulletins (WW). The NWS no longer uses that title or acronym for this product but retains WW

in the product header for processing by weather data systems.

EXAMPLE−

Example of a Public Tornado Watch Notification Message:

WWUS20 KWNS 050550

SEL2

SPC WW 051750

URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 243

NWS STORM PREDICTION CENTER NORMAN OK

1250 AM CDT MON MAY 5 2011

THE NWS STORM PREDICTION CENTER HAS ISSUED A

*TORNADO WATCH FOR PORTIONS OF

WESTERN AND CENTRAL ARKANSAS

SOUTHERN MISSOURI

F AR EASTERN OKLAHOMA

*EFFECTIVE THIS MONDAY MORNING FROM 1250 AM UNTIL 600 AM CDT.

...THIS IS A P ARTICULARLY DANGEROUS SITUATION...

*PRIMARY THREATS INCLUDE

NUMEROUS INTENSE TORNADOES LIKELY

NUMEROUS SIGNIFICANT DAMAGING WIND GUSTS TO 80 MPH LIKELY

NUMEROUS VERY LARGE HAIL TO 4 INCHES IN DIAMETER LIKELY

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 100 STATUTE MILES EAST AND WEST OF A LINE

FROM 15 MILES WEST NORTHWEST OF FORT LEONARD WOOD MISSOURI TO 45 MILES SOUTHWEST OF HOT

SPRINGS ARKANSAS. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE

UPDATE (WOUS64 KWNS WOU2).

REMEMBER...A TORNADO WATCH M EANS CONDITIONS ARE F AVORABLE FOR TORNADOES AND SEVERE

THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA. PERSONS IN THESE AREAS SHOULD BE ON THE

LOOKOUT FOR THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS AND POSSIBLE

WARNINGS.

OTHER WATCH INFORMATION...THIS TORNADO WATCH REPLACES TORNADO WATCH NUMBER 237. WATCH

NUMBER 237 WILL NOT BE IN EFFECT AFTER

1250 AM CDT. CONTINUE...WW 239...WW 240...WW 241...WW 242...

DISCUSSION...SRN MO SQUALL LINE EXPECTED TO CONTINUE EWD...WHERE LONG/HOOKED HODOGRAPHS

SUGGEST THREAT FOR EMBEDDED SUPERCELLS/PO SSIBLE TORNADOES. F ARTHER S...MORE WIDELY

SCATTERED

SUPERCELLS WITH A THREAT FOR TORNADOES WILL PERSIST IN VERY STRONGLY DEEP SHEARED/LCL

ENVIRONMENT IN AR.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERS TORMS WITH HAIL SURF ACE AND ALOFT TO 4

INCHES. EXTREME TURBULENCE AND SURF ACE WIND GUSTS TO 70 KNOTS. A FEW CUMULONIMBI WITH

MAXIMUM TOPS TO 500. MEAN STORM MOTION VECTOR 26045.

5. Status reports are issued as needed to show progress of storms and to delineate areas no longer under the

threat of severe storm activity. Cancellation bulletins are issued when it becomes evident that no severe weather

will develop or that storms have subsided and are no longer severe.

h. Center Weather Advisories (CWAs)

1. CWAs are unscheduled inflight, flow control, air traffic, and air crew advisory. By nature of its short lead

time, the CW A is not a flight planning product. It is generally a nowcast for conditions beginning within the next

two hours. CWAs will be issued:

Meteorology 7−1−21

AIM 2/20/253/15/077110.65R CHG 2AIM 8/7/25

(a) As a supplement to an existing SIGMET, Convective SIGMET or AIRMET.

(b) When an Inflight Advisory has not been issued but observed or expected weather conditions meet

SIGMET/AIRMET criteria based on current pilot reports and reinforced by other sources of information about

existing meteorological conditions.

AIRMET criteria; e.g., in terms of intensity or area coverage, but current pilot reports or other weather

information sources indicate that existing or anticipated meteorological phenomena will adversely affect the safe

flow of air traffic within the ARTCC area of responsibility.

2. The following example is a CWA issued from the Kansas City, Missouri, ARTCC. The “3” after ZKC

in the first line denotes this CWA has been issued for the third weather phenomena to occur for the day. The “301”

in the second line denotes the phenomena number again (3) and the issuance number (01) for this phenomena.

The CWA was issued at 2140Z and is valid until 2340Z.

EXAMPLE−

ZKC3 CWA 032140

ZKC CWA 301 VALID UNTIL 032340

ISOLD SVR TSTM over KCOU MOVG SWWD 10 KTS ETC.

7−1−7. Categorical Ceiling and Visibility Conditions

a. Categorical terms, describing either reported or forecast general ceiling and visibility conditions, are

defined as follows:

1. LIFR (Low IFR). Ceiling less than 500 feet and/or visibility less than 1 mile.

2. IFR. Ceiling 500 to less than 1,000 feet and/or visibility 1 to less than 3 miles.

3. MVFR (Marginal VFR). Ceiling 1,000 to 3,000 feet and/or visibility 3 to 5 miles inclusive.

4. VFR. Ceiling greater than 3,000 feet and visibility greater than 5 miles; includes sky clear.

b. The cause of LIFR, IFR, or MVFR is indicated by either ceiling or visibility restrictions or both. The

contraction “CIG” and/or weather and obstruction to vision symbols are used. If winds or gusts of 25 knots or

greater are forecast for the outlook period, the word “WIND” is also included for all categories including VFR.

EXAMPLE−

1. LIFR CIG−low IFR due to low ceiling.

2. IFR FG−IFR due to visibility restricted by fog.

3. MVFR CIG HZ FU−marginal VFR due to both ceiling and visibility restricted by haze and smoke.

4. IFR CIG RA WIND−IFR due to both low ceiling and visibility restricted by rain; wind expected to be 25 knots or greater .

7−1−8. Inflight Weather Advisory Broadcasts

a. ARTCCs broadcast a Convective SIGMET, SIGMET, AIRMET (except in the contiguous U.S.), Urgent

Pilot Report, or CWA alert once on all frequencies, except emergency frequencies, when any part of the area

described is within 150 miles of the airspace under their jurisdiction. These broadcasts advise pilots of the

availability of hazardous weather advisories and to contact the nearest flight service facility for additional details.

EXAMPLE−

1. Attention all aircraft, SIGMET Delta Three, from Myton to Tuba City to Milford, severe turbulence and severe clear icing

below one zero thousand feet. Expected to continue beyond zero three zero zero zulu.

2. Attention all aircraft, convective SIGMET Two Seven Eastern. From the vicinity of Elmira to Phillipsburg. Scattered

embedded thunderstorms moving east at one zero knots. A few intense level five cells, maximum tops four five zero.

3. Attention all aircraft, Kansas City Center weather advisory one zero three. Numerous reports of moderate to severe icing

from eight to niner thousand feet in a three zero mile radius of St. Louis. Light or negative icing reported from four thousand

to one two thousand feet remainder of Kansas City Center area.

7−1−22 Meteorology

2/20/25 AIM

NOTE−

Terminal control facilities have the option to limit hazardous weather information broadcast as follows: Tower cab and

approach control positions may opt to broadcast hazardous weather information alerts only when any part of the area

described is within 50 miles of the airspace under their jurisdiction.

REFERENCE−

F AA Order JO 7110.65, Para 2−6−6, Hazardous Inflight Weather Advisory.

7−1−9. Flight Information Services (FIS)

FIS is a method of disseminating meteorological (MET) and aeronautical information (AI) to displays in the

cockpit in order to enhance pilot situational awareness, provide decision support tools, and improve safety. FIS

augments traditional pilot voice communication with Flight Service Stations (FSSs), ATC facilities, or Airline

Operations Control Centers (AOCCs). FIS is not intended to replace traditional pilot and controller/flight service

specialist/aircraft dispatcher preflight briefings or inflight voice communications. FIS, however, can provide

textual and graphical information that can help abbreviate and improve the usefulness of such communications.

FIS enhances pilot situational awareness and improves safety.

a. Data link Service Providers (DSPs). DSPs deploy and maintain airborne, ground−based, and, in some cases,

space−based infrastructure that supports the transmission of AI/MET information over one or more physical

links. A DSP may provide a free of charge or a for−fee service that permits end users to uplink and downlink

AI/MET and other information. The following are examples of DSPs:

1. FAA FIS-B. A ground-based broadcast service provided through the ADS-B Universal Access

Transceiver (UAT) network. The service provides users with a 978 MHz data link capability when operating

within range and line-of-sight of a transmitting ground station. FIS-B enables users of properly equipped aircraft

to receive and display a suite of broadcast weather and aeronautical information products.

2. Non-FAA FIS Systems. Several commercial vendors provide customers with FIS data over both the

aeronautical spectrum and on other frequencies using a variety of data link protocols. Services available from

these providers vary greatly and may include tier based subscriptions. Advancements in bandwidth technology

permits preflight as well as inflight access to the same MET and AI information available on the ground. Pilots

and operators using non-FAA FIS for MET and AI information should be knowledgeable regarding the weather

services being provided as some commercial vendors may be repackaging NWS sourced weather, while other

commercial vendors may alter the weather information to produce vendor−tailored or vendor−specific weather

reports and forecasts.

b. Three Data Link Modes. There are three data link modes that may be used for transmitting AI and MET

information to aircraft. The intended use of the AI and/or MET information will determine the most appropriate

data link service.

1. Broadcast Mode: A one-way interaction in which AI and/or MET updates or changes applicable to a

designated geographic area are continuously transmitted (or transmitted at repeated periodic intervals) to all

aircraft capable of receiving the broadcast within the service volume defined by the system network architecture.

2. Contract/Demand Mode: A two-way interaction in which AI and/or MET information is transmitted to

an aircraft in response to a specific request.

3. Contract/Update Mode: A two-way interaction that is an extension of the Demand Mode. Initial AI

and/or MET report(s) are sent to an aircraft and subsequent updates or changes to the AI and/or MET information

that meet the contract criteria are automatically or manually sent to an aircraft.

c. To ensure airman compliance with Federal Aviation Regulations, manufacturer’s operating manuals should

remind airmen to contact ATC controllers, FSS specialists, operator dispatchers, or airline operations control

centers for general and mission critical aviation weather information and/or NAS status conditions (such as

NOTAMs, Special Use Airspace status, and other gove rnment flight information). If FIS products are

systemically modified (for example, are displayed as abbreviated plain text and/or graphical depictions), the

modification process and limitations of the resultant product should be clearly described in the vendor’s user

guidance.

Meteorology 7−1−23

AIM 2/20/25

d. Operational Use of FIS. Regardless of the type of FIS system being used, several factors must be considered

when using FIS:

1. Before using FIS for inflight operations, pilots and other flight crewmembers should become familiar

with the operation of the FIS system to be used, the airborne equipment to be used, including its system

architecture, airborne system components, coverage service volume and other limitations of the particular

system, modes of operation and indications of various system failures. Users should also be familiar with the

specific content and format of the services available from the FIS provider(s). Sources of information that may

provide this specific guidance include manufacturer’s manuals, training programs, and reference guides.

2. FIS should not serve as the sole source of aviation weather and other operational information. ATC, FSSs,

and, if applicable, AOCC VHF/HF voice remain as a redundant method of communicating aviation weather,

NOTAMs, and other operational information to aircraft in flight. FIS augments these traditional

ATC/FSS/AOCC services and, for some products, offers the advantage of being displayed as graphical

information. By using FIS for orientation, the usefulness of information received from conventional means may

be enhanced. For example, FIS may alert the pilot to specific areas of concern that will more accurately focus

requests made to FSS or AOCC for inflight updates or similar queries made to ATC.

3. The airspace and aeronautical environment is constantly changing. These changes occur quickly and

without warning. Critical operational decisions should be based on use of the most current and appropriate data

available. When differences exist between FIS and information obtained by voice communication with ATC,

FSS, and/or AOCC (if applicable), pilots are cautioned to use the most recent data from the most authoritative

source.

4. FIS aviation weather products (for example, graphical ground−based radar precipitation depictions) are

not appropriate for tactical (typical timeframe of less than 3 minutes) avoidance of severe weather such as

negotiating a path through a weather hazard area. FIS supports strategic (typical timeframe of 20 minutes or

more) weather decision−making such as route selection to avoid a weather hazard area in its entirety. The misuse

of information beyond its applicability may place the pilot and aircraft in jeopardy. In addition, FIS should never

be used in lieu of an individual preflight weather and flight planning briefing.

5. DSPs offer numerous MET and AI products with information that can be layered on top of each other.

Pilots need to be aware that too much information can have a negative effect on their cognitive work load. Pilots

need to manage the amount of information to a level that offers the most pertinent information to that specific

flight without creating a cockpit distraction. Pilots may need to adjust the amount of information based on

numerous factors including, but not limited to, the phase of flight, single pilot operation, autopilot availability,

class of airspace, and the weather conditions encountered.

6. FIS NOTAM products, including Temporary Flight Restriction (TFR) information, are advisory −use

information and are intended for situational awareness purposes only. Cockpit displays of this information are

not appropriate for tactical navigation − pilots should stay clear of any geographic area displayed as a TFR

NOTAM. Pilots should contact FSSs and/or ATC while en route to obtain updated information and to verify the

cockpit display of NOTAM information.

7. FIS supports better pilot decision−making by increasing situational awareness. Better decision−making

is based on using information from a variety of sources. In addition to FIS, pilots should take advantage of other

weather/NAS status sources, including, briefings from Flight Service Stations, data from other air traffic control

facilities, airline operation control centers, pilot reports, as well as their own observations.

e. FAA’s Flight Information Service−Broadcast (FIS−B).

1. FIS−B is a ground− based broadcast service provided through the FAA’s Automatic Dependent

Surveillance–Broadcast (ADS−B) Services Universal Access Transceiver (UAT) network. The service provides

users with a 978 MHz data link capability when operating within range and line−of−sight of a transmitting ground

station. FIS−B enables users of properly−equipped aircraft to receive and display a suite of broadcast weather

and aeronautical information products.

7−1−24 Meteorology

AIM2/20/258/7/25 AIM

2. TBL 7−1−3 lists the text and graphical products available through FIS−B and provided free−of−charge.

Detailed information concerning FIS−B meteorological products can be found in FAA−H−8083−28, Aviation

Weather Handbook, and AC 00–63, Use of Cockpit Displays of Digital Weather and Aeronautical Information.

Information on Special Use Airspace (SUA), Temporary Flight Restriction (TFR), and Notice to Airmen

(NOTAM) products can be found in Chapters 3, 4, and 5 of this manual.

3. Users of FIS−B should familiarize themselves with the operational characteristics and limitations of the

system, including: system architecture; service envi ronment; product lifecycles; modes of operation; and

indications of system failure.

NOTE−

The NOTAM−D and NOTAM−FDC products broadcast via FIS−B are limited to those issued or effective within the past 30

days. Except for TFRs, NOTAMs older than 30 days are not provided. The pilot in command is responsible for reviewing

all necessary information prior to flight.

4. FIS−B products are updated and transmitted at specific intervals based primarily on product issuance

criteria. Update intervals are defined as the rate at which the product data is available from the source for

transmission. Transmission intervals are defined as the amount of time within which a new or updated product

transmission must be completed and/or the rate or repetition interval at which the product is rebroadcast. Update

and transmission intervals for each product are provided in TBL 7−1−3.

5. Where applicable, FIS−B products include a look−ahead range expressed in nautical miles (NM) for three

service domains: Airport Surface; Terminal Airspace; and En Route/Gulf of America. TBL 7 −1−4 provides

service domain availability and look−ahead ranging for each FIS−B product.

6. Prior to using this capability, users should familiarize themselves with the operation of FIS−B avionics

by referencing the applicable User’s Guides. Guidance concerning the interpretation of information displayed

should be obtained from the appropriate avionics manufacturer.

7. FIS−B malfunctions not attributed to aircraft system failures or covered by active NOTAM should be

reported by radio or telephone to the nearest FSS facility, or by sending an email to the ADS−B help desk at

[email protected]. Reports should include:

(a) Condition observed;

(b) Date and time of observation;

(d) Type and call sign of the aircraft; and

(e) Type and software version of avionics system.

f. Non−FAA FIS Systems. Several commercial vendors also provide customers with FIS data over both the

aeronautical spectrum and on other frequencies using a variety of data link protocols. In some cases, the vendors

provide only the communications system that carries customer messages, such as the Aircraft Communications

Addressing and Reporting System (ACARS) used by many air carrier and other operators.

1. Operators using non−FAA FIS data for inflight weather and other operational information should ensure

that the products used conform to FAA/NWS standa rds. Specifically, aviation weather and NAS status

information should meet the following criteria:

(a) The products should be either FAA/NWS “accepted” aviation weather reports or products, or based

on FAA/NWS accepted aviation weather reports or products. If products are used which do not meet this criteria,

they should be so identified. The operator must determine the applicability of such products to their particular

flight operations.

(b) In the case of a weather product which is the result of the application of a process which alters the

form, function or content of the base FAA/NWS accepted weather product(s), that process, and any limitations

to the application of the resultant product, should be described in the vendor’s user guidance material. An

Meteorology 7−1−25

AIM 2/20/25

example would be a NEXRAD radar composite/mosaic map, which has been modified by changing the scaling

resolution. The methodology of assigning reflectivity values to the resultant image components should be

described in the vendor’s guidance material to ensure that the user can accurately interpret the displayed data.

TBL 7−1−3

FIS−B Over UAT Product Update and Transmission Intervals

Product Update Interval1 Transmission

Interval (95%)2

Basic

Product

AIRMET As Available 5 minutes Yes

AWW/WW As Available, then at 15 minute

intervals for 1 hour 5 minutes No

Ceiling As Available 10 minutes No

Convective SIGMET As Available, then at 15 minute

intervals for 1 hour 5 minutes Yes

D−A TIS As Available 1 minute No

Echo Top 5 minutes 5 minutes No

METAR/SPECI 1 minute (where available), As

Available otherwise 5 minutes Yes

MRMS NEXRAD (CONUS) 2 minutes 15 minutes Yes

MRMS NEXRAD (Regional) 2 minutes 2.5 minutes Yes

NOTAMs−D/FDC As Available 10 minutes Yes

NOTAMs−TFR As Available 10 minutes Yes

PIREP As Available 10 minutes Yes

SIGMET As Available, then at 15 minute

intervals for 1 hour 5 minutes Yes

SUA Status As Available 10 minutes Yes

TAF/AMEND 6 Hours (±15 minutes) 10 minutes Yes

Temperature Aloft 12 Hours (±15 minutes) 10 minutes Yes

TWIP As Available 1 minute No

Winds aloft 12 Hours (±15 minutes) 10 minutes Yes

Lightning strikes 3 5 minutes 5 minutes Yes

Turbulence 3 1 minute 15 minutes Yes

Icing, Forecast Potential (FIP) 3 60 minutes 15 minutes Yes

Cloud tops 3 30 minutes 15 minutes Yes

1 Minute AWOS 3 1 minute 10 minutes No

Graphical−AIRMET 3 As Available 5 minutes Yes

Center Weather Advisory (CWA) 3 As Available 10 minutes Yes

Temporary Restricted Areas (TRA) As Available 10 minutes Yes

Temporary Military Operations Areas

(TMOA) As Available 10 minutes Yes

1 The Update Interval is the rate at which the product data is available from the source.

7−1−26 Meteorology

2/20/25 AIM

2 The Transmission Interval is the amount of time within which a new or updated product transmission must be completed

(95%) and the rate or repetition interval at which the product is rebroadcast (95%).

3 The transmission and update intervals for the expanded set of basic meteorological products may be adjusted based on FAA

and vendor agreement on the final product formats and performance requirements.

NOTE−

1. Details concerning the content, format, and symbols of the various data link products provided should be obtained from

the specific avionics manufacturer.

2. NOTAM−D and NOTAM−FDC products broadcast via FIS−B are limited to those issued or effective within the past 30

days.

TBL 7−1−4

Product Parameters for Low/Medium/High Altitude Tier Radios

Product Surface Radios Low Altitude Tier Medium Altitude

Tier

High Altitude Tier

CONUS NEXRAD N/A CONUS NEXRAD CONUS NEXRAD CONUS NEXRAD

not provided imagery imagery

Winds & Temps 500 NM look−ahead 500 NM look−ahead 750 NM look−ahead 1,000 NM look−

Aloft range range range ahead range

METAR 100 NM look−ahead 250 NM look−ahead 375 NM look−ahead CONUS: CONUS

range range range Class B & C airport

METARs and 500

NM look−ahead

range

Outside of CONUS:

500 NM look-ahead

range

TAF 100 NM look−ahead 250 NM look−ahead 375 NM look−ahead CONUS: CONUS

range range range Class B & C airport

TAFs and 500 NM

look−ahead range

Outside of CONUS:

500 NM look-ahead

range

AIRMET, SIGMET, 100 NM look−ahead 250 NM look−ahead 375 NM look−ahead 500 NM look−ahead

PIREP, and SUA/ range. PIREP/SUA/ range range range

SAA SAA is N/A.

Regional NEXRAD 150 NM look−ahead 150 NM look−ahead 200 NM look−ahead 250 NM look−ahead

range range range range

NOTAMs D, FDC, 100 NM look−ahead 100 NM look−ahead 100 NM look−ahead 100 NM look−ahead

and TFR range range range range

7−1−10. Weather Observing Programs

a. Manual Observations. With only a few exceptions, these reports are from airport locations staffed by

FAA personnel who manually observe, perform calculations, and enter these observations into the (WMSCR)

communication system. The format and coding of these observations are contained in paragraph 7−1−28 , Key

to Aviation Routine Weather Report (METAR) and Aerodrome Forecasts (TAF).

b. Automated Weather Observing System (AWOS).

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AIM 2/20/25

1. Automated weather reporting systems are increasingly being installed at airports. These systems consist

of various sensors, a processor, a computer-generated voice subsystem, and a transmitter to broadcast local,

minute-by-minute weather data directly to the pilot.

NOTE−

When the barometric pressure exceeds 31.00 inches Hg., see AIM, Para 7−2−3, Altimeter Errors.

2. The AWOS observations will include the prefix “AUTO” to indicate that the data are derived from an

automated system. Some AWOS locations will be augmented by certified observers who will provide weather

and obstruction to vision information in the remarks of the report when the reported visibility is less than 7 miles.

These sites, along with the hours of augmentation, are to be published in the Chart Supplement. Augmentation

is identified in the observation as “OBSERVER WEATHER.” The AWOS wind speed, direction and gusts,

temperature, dew point, and altimeter setting are exactly the same as for manual observations. The AWOS will

also report density altitude when it exceeds the field elevation by more than 1,000 feet. The reported visibility

is derived from a sensor near the touchdown of the primary instrument runway. The visibility sensor output is

converted to a visibility value using a 10−minute harmonic average. The reported sky condition/ceiling is derived

from the ceilometer located next to the visibility sensor. The AWOS algorithm integrates the last 30 minutes of

ceilometer data to derive cloud layers and heights. This output may also differ from the observer sky condition

in that the AWOS is totally dependent upon the cloud advection over the sensor site.

3. These real-time systems are operationally classified into nine basic levels:

(a) AWOS−A only reports altimeter setting;

NOTE−

Any other information is advisory only.

(b) AWOS−AV reports altimeter and visibility;

NOTE−

Any other information is advisory only.

(d) AWOS−2 provides the information provided by AWOS−l plus visibility; and

(e) AWOS−3 provides the information provided by AWOS−2 plus cloud/ceiling data.

(f) AWOS− 3P provides reports the same as the AWOS 3 system, plus a precipitation identification

sensor.

(g) AWOS− 3PT reports the same as the AWOS 3P System, plus thunderstorm/lightning reporting

capability.

(h) AWOS− 3T reports the same as AWOS 3 system and includes a thunderstorm/lightning reporting

capability.

(i) AWOS− 4 reports the same as the AWOS 3 system, plus precipitation occurrence, type and

accumulation, freezing rain, thunderstorm, and runway surface sensors.

4. The information is transmitted over a discrete VHF radio frequency or the voice portion of a local

NA V AID. AWOS transmissions on a discrete VHF radio frequency are engineered to be receivable to a maximum

of 25 NM from the AWOS site and a maximum altitude of 10,000 feet AGL. At many locations, AWOS signals

may be received on the surface of the airport, but local conditions may limit the maximum AWOS reception

distance and/or altitude. The system transmits a 20 to 30 second weather message updated each minute. Pilots

should monitor the designated frequency for the automated weather broadcast. A description of the broadcast

is contained in subparagraph c. There is no two-way communication capability. Most AWOS sites also have a

dial-up capability so that the minute-by-minute weather messages can be accessed via telephone.

5. AWOS information (system level, frequency, phone number, etc.) concerning specific locations is

published, as the systems become operational, in the Chart Supplement, and where applicable, on published

7−1−28 Meteorology

2/20/25 AIM

Instrument Approach Procedures. Selected individual systems may be incorporated into nationwide data

collection and dissemination networks in the future.

c. AWOS Broadcasts. Computer-generated voice is used in AWOS to automate the broadcast of the

minute-by-minute weather observations. In addition, some systems are configured to permit the addition of an

operator-generated voice message; e.g., weather remarks following the automated parameters. The phraseology

used generally follows that used for other weather broadcasts. Following are explanations and examples of the

exceptions.

1. Location and Time. The location/name and the phrase “AUTOMATED WEATHER OBSERV A-

TION,” followed by the time are announced.

(a) If the airport’s specific location is included in the airport’s name, the airport’s name is announced.

EXAMPLE−

“Bremerton National Airport automated weather observation, one four five six zulu;”

“Ravenswood Jackson County Airport automated weather observation, one four five six zulu.”

(b) If the airport’s specific location is not included in the airport’s name, the location is announced

followed by the airport’s name.

EXAMPLE−

“Sault Ste. Marie, Chippewa County International Airport automated weather observation;”

“Sandusky, Cowley Field automated weather observation.”

status.

EXAMPLE−

“Bremerton National Airport automated weather observation test, one four five six zulu.”

(d) The phrase “TEMPORARILY INOPERATIVE” is added when the system is inoperative.

EXAMPLE−

“Bremerton National Airport automated weather observing system temporarily inoperative.”

2. Visibility.

(a) The lowest reportable visibility value in AWOS is “less than 1/4.” It is announced as “VISIBILITY

LESS THAN ONE QUARTER.”

(b) A sensor for determining visibility is not included in some AWOS. In these systems, visibility is not

announced. “VISIBILITY MISSING” is announced only if the system is configured with a visibility sensor and

visibility information is not available.

3. Weather. In the future, some AWOSs are to be configured to determine the occurrence of precipitation.

However, the type and intensity may not always be determined. In these systems, the word “PRECIPITATION”

will be announced if precipitation is occurring, but the type and intensity are not determined.

4. Ceiling and Sky Cover.

(a) Ceiling is announced as either “CEILING” or “INDEFINITE CEILING.” With the exception of

indefinite ceilings, all automated ceiling heights are measured.

EXAMPLE−

“Bremerton National Airport automated weather observation, one four five six zulu. Ceiling two thousand overcast;”

“Bremerton National Airport automated weather observation, one four five six zulu. Indefinite ceiling two hundred, sky

obscured.”

(b) The word “Clear” is not used in AWOS due to limitations in the height ranges of the sensors. No

clouds detected is announced as “NO CLOUDS BELOW XXX” or, in newer systems as “CLEAR BELOW

XXX” (where XXX is the range limit of the sensor).

Meteorology 7−1−29

AIM 2/20/25

EXAMPLE−

“No clouds below one two thousand.”

“Clear below one two thousand.”

ceiling and sky cover are not announced. “SKY CONDITION MISSING” is announced only if the system is

configured with a ceilometer and the ceiling and sky cover information is not available.

5. Remarks. If remarks are included in the observation, the word “REMARKS” is announced following

the altimeter setting.

(a) Automated “Remarks.”

(1) Density Altitude.

(2) Variable Visibility.

(3) Variable Wind Direction.

(b) Manual Input Remarks. Manual input remarks are prefaced with the phrase “OBSERVER

WEATHER.” As a general rule the manual remarks are limited to:

(1) Type and intensity of precipitation.

(2) Thunderstorms and direction; and

(3) Obstructions to vision when the visibility is 3 miles or less.

EXAMPLE−

“Remarks ... density altitude, two thousand five hundred ... visibility variable between one and two ... wind direction variable

between two four zero and three one zero ...observed we ather ... thunderstorm moderate rain showers and fog ...

thunderstorm overhead.”

parameter is announced as “MISSING.” For example, a report with the dew point “missing” and no manual input

available, would be announced as follows:

EXAMPLE−

“Ceiling one thousand overcast ... visibility three ... precipitation ... temperature three zero, dew point missing ... wind calm

... altimeter three zero zero one.”

(d) “REMARKS” are announced in the following order of priority:

(1) Automated “REMARKS.”

[a] Density Altitude.

[b] Variable Visibility.

[c] Variable Wind Direction.

(2) Manual Input “REMARKS.”

[a] Sky Condition.

[b] Visibility.

[c] Weather and Obstructions to Vision.

[d] Temperature.

[e] Dew Point.

[f] Wind; and

[g] Altimeter Setting.

EXAMPLE−

“Remarks ... density altitude, two thousand five hundred ... visibility variable between one and two ... wind direction variable

7−1−30 Meteorology

2/20/25 AIM

between two four zero and three one zero ... observer ceiling estimated two thousand broken ... observer temperature two,

dew point minus five.”

d. Automated Surface Observing System (ASOS)/Automated Weather Observing System

(AWOS) The ASOS/AWOS is the primary surface weather observing system of the U.S. (See Key to Decode

an ASOS/AWOS (METAR) Observation, FIG 7−1−8 and FIG 7−1−9.) The program to install and operate these

systems throughout the U.S. is a joint effort of the NWS, the FAA and the Department of Defense. ASOS/AWOS

is designed to support aviation operations and weather forecast activities. The ASOS/AWOS will provide

continuous minute-by-minute observations and perform the basic observing functions necessary to generate an

aviation routine weather report (METAR) and other aviation weather information. The information may be

transmitted over a discrete VHF radio frequency or the voice portion of a local NA V AID. ASOS/AWOS

transmissions on a discrete VHF radio frequency are engineered to be receivable to a maximum of 25 NM from

the ASOS/AWOS site and a maximum altitude of 10,000 feet AGL. At many locations, ASOS/AWOS signals

may be received on the surface of the airport, but local conditions may limit the maximum reception distance

and/or altitude. While the automated system and the human may differ in their methods of data collection and

interpretation, both produce an observation quite similar in form and content. For the “objective” elements such

as pressure, ambient temperature, dew point temperature, wind, and precipitation accumulation, both the

automated system and the observer use a fixed location and time-averaging technique. The quantitative

differences between the observer and the automated observation of these elements are negligible. For the

“subjective” elements, however, observers use a fixed time, spatial averaging technique to describe the visual

elements (sky condition, visibility and present weather), while the automated systems use a fixed location, time

averaging technique. Although this is a fundamental change, the manual and automated techniques yield

remarkably similar results within the limits of their respective capabilities.

1. System Description.

(a) The ASOS/AWOS at each airport location consists of these main components:

(1) Individual weather sensors.

(2) Data collection and processing units.

(3) Peripherals and displays.

(b) The ASOS/AWOS sensors perform the basic function of data acquisition. They continuously sample

and measure the ambient environment, derive raw sensor data and make them available to the collection and

processing units.

2. Every ASOS/AWOS will contain the following basic set of sensors:

(a) Cloud height indicator (one or possibly three).

(b) Visibility sensor (one or possibly three).

(d) Freezing rain sensor (at select sites).

(e) Pressure sensors (two sensors at small airports; three sensors at large airports).

(f) Ambient temperature/Dew point temperature sensor.

(g) Anemometer (wind direction and speed sensor).

(h) Rainfall accumulation sensor.

(i) Automated Lightning Detection and Reporting System (ALDARS) (excluding Alaska and Pacific

Island sites).

3. The ASOS/AWOS data outlets include:

(a) Those necessary for on-site airport users.

Meteorology 7−1−31

AIM 2/20/25

(b) National communications networks.

line).

NOTE−

Wind direction is reported relative to magnetic north in ATIS as well as ASOS and AWOS radio (voice) broadcasts.

4. An ASOS/AWOS report without human intervention will contain only that weather data capable of being

reported automatically. The modifier for this METAR report is “AUTO.” When an observer augments or

backs−up an ASOS/AWOS site, the “AUTO” modifier disappears.

5. There are two types of automated stations, AO1 for automated weather reporting stations without a

precipitation discriminator, and AO2 for automated stations with a precipitation discriminator. As appropriate,

“AO1” and “AO2” must appear in remarks. (A precipitation discriminator can determine the difference between

liquid and frozen/freezing precipitation).

NOTE−

To decode an ASOS/AWOS report, refer to FIG 7−1−8 and FIG 7−1−9.

REFERENCE−

A complete explanation of METAR terminology is located in AIM, Para 7−1−28, Key to Aerodrome Forecast (TAF) and Aviation Routine Weather Report

(METAR).

7−1−32 Meteorology

2/20/25 AIM

FIG 7−1−8

Key to Decode an ASOS/AWOS (METAR) Observation (Front)

Meteorology 7−1−33

AIM 2/20/25

FIG 7−1−9

Key to Decode an ASOS/AWOS (METAR) Observation (Back)

7−1−34 Meteorology

2/20/25 AIM

e. TBL 7−1−5 contains a comparison of weather observing programs and the elements reported.

f. Service Standards. During 1995, a government/industry team worked to comprehensively reassess the

requirements for surface observations at the nation’s airports. That work resulted in agreement on a set of service

standards, and the FAA and NWS ASOS sites to which the standards would apply. The term “Service Standards”

refers to the level of detail in weather observation. The service standards consist of four different levels of service

(A, B, C, and D) as described below. Specific observational elements included in each service level are listed

in TBL 7−1−6.

1. Service Level D defines the minimum acceptable level of service. It is a completely automated service

in which the ASOS/AWOS observation will constitute the entire observation, i.e., no additional weather

information is added by a human observer. This service is referred to as a stand alone D site.

2. Service Level C is a service in which the human observer, usually an air traffic controller, augments or

adds information to the automated observation. Service Level C also includes backup of ASOS/AWOS elements

in the event of an ASOS/AWOS malfunction or an unrepresentative ASOS/AWOS report. In backup, the human

observer inserts the correct or missing value for the automated ASOS/AWOS elements. This service is provided

by air traffic controllers under the Limited Aviation Weather Reporting Station (LAWRS) process, FSS and NWS

observers, and, at selected sites, Non−Federal Observation Program observers.

Two categories of airports require detail beyond Service Level C in order to enhance air traffic control efficiency

and increase system capacity. Services at these airports are typically provided by contract weather observers,

NWS observers, and, at some locations, FSS observers.

3. Service Level B is a service in which weather observations consist of all elements provided under Service

Level C, plus augmentation of additional data beyond the capability of the ASOS/AWOS. This category of

airports includes smaller hubs or special airports in other ways that have worse than average bad weather

operations for thunderstorms and/or freezing/frozen precipitation, and/or that are remote airports.

4. Service Level A, the highest and most demanding category, includes all the data reported in Service

Standard B, plus additional requirements as specified. Service Level A covers major aviation hubs and/or high

volume traffic airports with average or worse weather.

TBL 7−1−5

Weather Observing Programs

Element

Reported

Type

Wind

Visibility

Temperature

Dew Point

Altimeter

Density

Altimeter

Cloud/Ceiling

Precipitation

Identification

Thunderstorm/

Lightning

Precipitation

Occurrence

Rainfall

Accumulation

Runway Surface

Condition

Freezing Rain

Occurrence

Remarks

ASOS X X X X X X X X X X

AWOS−A X

AWOS−A/V X X

AWOS−1 X X X X

AWOS−2 X X X X X

AWOS−3 X X X X X X

AWOS−3P X X X X X X X

AWOS−3T X X X X X X X

AWOS−3P/T X X X X X X X X

AWOS−4 X X X X X X X X X X X X

Manual X X X X X X X

REFERENCE− FAA Order JO 7900.5, Surface Weather Observing, for element reporting.

Meteorology 7−1−35

AIM 2/20/25

TBL 7−1−6

SERVICE LEVEL A

Service Level A consists of all the elements of

Service Levels B, C and D plus the elements

listed to the right, if observed.

10 minute longline RVR at precedented sites or

additional visibility increments of 1/8, 1/16 and 0

Sector visibility

Variable sky condition

Cloud layers above 12,000 feet and cloud types

Widespread dust, sand and other obscurations

V olcanic eruptions

SERVICE LEVEL B

Service Level B consists of all the elements of

Service Levels C and D plus the elements listed to

the right, if observed.

Longline RVR at precedented sites

(may be instantaneous readout)

Freezing drizzle versus freezing rain

Ice pellets

Snow depth & snow increasing rapidly remarks

Thunderstorm and lightning location remarks

Observed significant weather not at the station

remarks

SERVICE LEVEL C

Service Level C consists of all the elements of Service

Level D plus augmentation and backup by a human

observer or an air traffic control specialist on location

nearby. Backup consists of inserting the correct value if

the system malfunctions or is unrepresentative.

Augmentation consists of adding the elements listed to

the right, if observed. During hours that the observing

facility is closed, the site reverts to Service Level D.

Thunderstorms

Tornadoes

Hail

Virga

V olcanic ash

Tower visibility

Operationally significant remarks as deemed

appropriate by the observer

SERVICE LEVEL D

This level of service consists of an ASOS or AWOS

continually measuring the atmosphere at a point near the

runway. The ASOS or AWOS senses and measures the

weather parameters listed to the right.

Wind

Visibility

Precipitation/Obstruction to vision

Cloud height

Sky cover

Temperature

Dew point

Altimeter

7−1−11. Weather Radar Services

a. The National Weather Service operates a network of radar sites for detecting coverage, intensity, and

movement of precipitation. The network is supplemented by FAA and DoD radar sites in the western sections

of the country. Local warning radar sites augment the network by operating on an as needed basis to support

warning and forecast programs.

b. Scheduled radar observations are taken hourly and transmitted in alpha-numeric format on weather

telecommunications circuits for flight planning purposes. Under certain conditions, special radar reports are

issued in addition to the hourly transmittals. Data contained in the reports are also collected by the National

Center for Environmental Prediction and used to prepare national radar summary charts for dissemination on

facsimile circuits.

c. A clear radar display (no echoes) does not mean that there is no significant weather within the coverage of

the radar site. Clouds and fog are not detected by the radar. However, when echoes are present, turbulence can

be implied by the intensity of the precipitation, and icing is implied by the presence of the precipitation at

temperatures at or below zero degrees Celsius. Used in conjunction with other weather products, radar provides

invaluable information for weather avoidance and flight planning.

Meteorology7−1−36

2/20/25 AIM

FIG 7−1−10

NEXRAD Coverage

Meteorology 7−1−37

AIM 2/20/25

FIG 7−1−11

NEXRAD Coverage

7−1−38 Meteorology

2/20/25 AIM

FIG 7−1−12

NEXRAD Coverage

Meteorology 7−1−39

AIM 2/20/25

d. All En Route Flight Advisory Service facilities and FSSs have equipment to directly access the radar

displays from the individual weather radar sites. Specialists at these locations are trained to interpret the display

for pilot briefing and inflight advisory services. The Center Weather Service Units located in ARTCCs also have

access to weather radar displays and provide support to all air traffic facilities within their center’s area.

e. For more detailed information on PIREPS, users can refer to the current version of the Aviation Weather

Handbook, FAA−H−8083−28.

REFERENCE−

Pilot/Controller Glossary Term− Precipitation Radar Weather Descriptions.

AIM, Para 7−1−26, Thunderstorms.

Chart Supplement, Charts, NWS Upper Air Observing Stations and Weather Network for the location of specific radar sites.

7−1−12. ATC Inflight Weather Avoidance Assistance

a. ATC Radar Weather Display.

1. ATC radars are able to display areas of precipitation by sending out a beam of radio energy that is reflected

back to the radar antenna when it strikes an object or moisture which may be in the form of rain drops, hail, or

snow. The larger the object is, or the more dense its reflective surface, the stronger the return will be presented.

Radar weather processors indicate the intensity of reflective returns in terms of decibels (dBZ). ATC systems

cannot detect the presence or absence of clouds. The ATC systems can often determine the intensity of a

precipitation area, but the specific character of that area (snow, rain, hail, VIRGA, etc.) cannot be determined.

For this reason, ATC refers to all weather areas displayed on ATC radar scopes as “precipitation.”

2. All A TC facilities using radar weather processors with the ability to determine precipitation intensity, will

describe the intensity to pilots as:

(a) “LIGHT” (< 26 dBZ)

(b) “MODERATE” (26 to 40 dBZ)

(d) “EXTREME” (> 50 dBZ)

NOTE−

En route ATC radar’ s Weather and Radar Processor (WARP) does not display light precipitation intensity.

3. ATC facilities that, due to equipment limitations, cannot display the intensity levels of precipitation, will

describe the location of the precipitation area by geographic position, or position relative to the aircraft. Since

the intensity level is not available, the controller will state “INTENSITY UNKNOWN.”

4. ARTCC facilities normally use a Weather and Radar Processor (WARP) to display a mosaic of data

obtained from multiple NEXRAD sites. There is a time delay between actual conditions and those displayed to

the controller. For example, the precipitation data on the ARTCC controller’s display could be up to 6 minutes

old. When the WARP is not available, a second system, the narrowband Air Route Surveillance Radar (ARSR)

can display two distinct levels of precipitation intensity that will be described to pilots as “MODERATE” (30

to 40 dBZ) and “HEA VY TO EXTREME” ( > 40 dBZ ). The WARP processor is only used in ARTCC facilities.

5. ATC radar is not able to detect turbulence. Generally, turbulence can be expected to occur as the rate of

rainfall or intensity of precipitation increases. Turbulence associated with greater rates of rainfall/precipitation

will normally be more severe than any associated with lesser rates of rainfall/precipitation. Turbulence should

be expected to occur near convective activity, even in clear air. Thunderstorms are a form of convective activity

that imply severe or greater turbulence. Operation within 20 miles of thunderstorms should be approached with

great caution, as the severity of turbulence can be markedly greater than the precipitation intensity might indicate.

b. Weather Avoidance Assistance.

1. To the extent possible, controllers will issue pertinent information on weather or chaff areas and assist

pilots in avoiding such areas when requested. Pilo ts should respond to a weather advisory by either

7−1−40 Meteorology

2/20/25 AIM

acknowledging the advisory or by acknowledging the advisory and requesting an alternative course of action as

follows:

(a) Request to deviate off course by stating a heading or degrees, direction of deviation, and approximate

number of miles. In this case, when the requested deviation is approved, navigation is at the pilot’s prerogative,

but must maintain the altitude assigned, and remain within the lateral restrictions issued by ATC.

(b) An approval for lateral deviation authorizes the pilot to maneuver left or right within the lateral limits

specified in the clearance.

NOTE−

1. It is often necessary for ATC to restrict the amount of lateral deviation (“twenty degrees right,” “up to fifteen degrees

left,” “up to ten degrees left or right of course”).

2. The term “when able, proceed direct,” in an ATC weather deviation clearance, refers to the pilot’ s ability to remain clear

of the weather when returning to course/route.

(d) Request a change of altitude.

(e) Request radar vectors around the affected areas.

2. For obvious reasons of safety, an IFR pilot must not deviate from the course or altitude or flight level

without a proper ATC clearance. When weather conditions encountered are so severe that an immediate deviation

is determined to be necessary and time will not permit approval by ATC, the pilot’s emergency authority may

be exercised.

3. When the pilot requests clearance for a route deviation or for an ATC radar vector, the controller must

evaluate the air traffic picture in the affected area, and coordinate with other controllers (if ATC jurisdictional

boundaries may be crossed) before replying to the request.

4. It should be remembered that the controller’s primary function is to provide safe separation between

aircraft. Any additional service, such as weather avoidance assistance, can only be provided to the extent that

it does not derogate the primary function. It’s also worth noting that the separation workload is generally greater

than normal when weather disrupts the usual flow of traffic. ATC radar limitations and frequency congestion may

also be a factor in limiting the controller’s capability to provide additional service.

5. It is very important, therefore, that the request for deviation or radar vector be forwarded to ATC as far

in advance as possible. Delay in submitting it may delay or even preclude ATC approval or require that additional

restrictions be placed on the clearance. Insofar as possible the following information should be furnished to A TC

when requesting clearance to detour around weather activity:

(a) Proposed point where detour will commence.

(b) Proposed route and extent of detour (direction and distance).

(d) Flight conditions (IFR or VFR).

(e) Any further deviation that may become necessary as the flight progresses.

(f) Advise if the aircraft is equipped with functioning airborne radar.

6. To a large degree, the assistance that might be rendered by ATC will depend upon the weather information

available to controllers. Due to the extremely transitory nature of severe weather situations, the controller’s

weather information may be of only limited value if based on weather observed on radar only. Frequent updates

by pilots giving specific information as to the area affected, altitudes, intensity and nature of the severe weather

can be of considerable value. Such reports are relayed by radio or phone to other pilots and controllers and also

receive widespread teletypewriter dissemination.

7. Obtaining IFR clearance or an ATC radar vector to circumnavigate severe weather can often be

accommodated more readily in the en route areas away from terminals because there is usually less congestion

Meteorology 7−1−41

AIM 2/20/25

and, therefore, offer greater freedom of action. In terminal areas, the problem is more acute because of traffic

density, ATC coordination requirements, complex departure and arrival routes, adjacent airports, etc. As a

consequence, controllers are less likely to be able to accommodate all requests for weather detours in a terminal

area or be in a position to volunteer such routing to the pilot. Nevertheless, pilots should not hesitate to advise

controllers of any observed severe weather and should specifically advise controllers if they desire

circumnavigation of observed weather.

7−1−13. Runway Visual Range (RVR)

There are currently two configurations of RVR in the NAS commonly identified as Taskers and New Generation

RVR. The Taskers are the existing configuration which uses transmissometer technology. The New Generation

RVRs were deployed in November 1994 and use forward scatter technology. The New Generation RVRs are

currently being deployed in the NAS to replace the existing Taskers.

a. RVR values are measured by transmissometers mounted on 14−foot towers along the runway. A full RVR

system consists of:

1. Transmissometer projector and related items.

2. Transmissometer receiver (detector) and related items.

3. Analog recorder.

4. Signal data converter and related items.

5. Remote digital or remote display programmer.

b. The transmissometer projector and receiver are mounted on towers 250 feet apart. A known intensity of

light is emitted from the projector and is measured by the receiver. Any obscuring matter such as rain, snow, dust,

fog, haze or smoke reduces the light intensity arriving at the receiver. The resultant intensity measurement is then

converted to an RVR value by the signal data converter. These values are displayed by readout equipment in the

associated air traffic facility and updated approximately once every minute for controller issuance to pilots.

c. The signal data converter receives information on the high intensity runway edge light setting in use (step 3,

4, or 5); transmission values from the transmissometer and the sensing of day or night conditions. From the three

data sources, the system will compute appropriate RVR values.

d. An RVR transmissometer established on a 250 foot baseline provides digital readouts to a minimum of 600

feet, which are displayed in 200 foot increments to 3,000 feet and in 500 foot increments from 3,000 feet to a

maximum value of 6,000 feet.

e. RVR values for Category IIIa operations extend down to 700 feet RVR; however, only 600 and 800 feet

are reportable RVR increments. The 800 RVR reportable value covers a range of 701 feet to 900 feet and is

therefore a valid minimum indication of Category IIIa operations.

f. Approach categories with the corresponding minimum RVR values. (See TBL 7−1−7.)

TBL 7−1−7

Approach Category/Minimum RVR Table

Category Visibility (RVR)

Nonprecision 2,400 feet

Category I 1,800 feet*

Category II 1,000 feet

Category IIIa 700 feet

Category IIIb 150 feet

Category IIIc 0 feet

* 1,400 feet with special equipment and authorization

7−1−42 Meteorology

2/20/25 AIM

g. Ten minute maximum and minimum RVR values for the designated RVR runway are reported in the body

of the aviation weather report when the prevailing visibility is less than one mile and/or the RVR is 6,000 feet

or less. ATCTs report RVR when the prevailing visibility is 1 mile or less and/or the RVR is 6,000 feet or less.

h. Details on the requirements for the operational use of RVR are contained in FAA AC 97−1, Runway Visual

Range (RVR). Pilots are responsible for compliance with minimums prescribed for their class of operations in

the appropriate CFRs and/or operations specifications.

i. RVR values are also measured by forward scatter meters mounted on 14−foot frangible fiberglass poles. A

full RVR system consists of:

1. Forward scatter meter with a transmitter, receiver and associated items.

2. A runway light intensity monitor (RLIM).

3. An ambient light sensor (ALS).

4. A data processor unit (DPU).

5. Controller display (CD).

j. The forward scatter meter is mounted on a 14−foot frangible pole. Infrared light is emitted from the

transmitter and received by the receiver. Any obscuring matter such as rain, snow, dust, fog, haze or smoke

increases the amount of scattered light reaching the receiver. The resulting measurement along with inputs from

the runway light intensity monitor and the ambient light sensor are forwarded to the DPU which calculates the

proper RVR value. The RVR values are displayed locally and remotely on controller displays.

k. The runway light intensity monitors both the runway edge and centerline light step settings (steps 1 through

5). Centerline light step settings are used for CAT IIIb operations. Edge Light step settings are used for CAT I,

II, and IIIa operations.

l. New Generation RVRs can measure and display RVR values down to the lowest limits of Category IIIb

operations (150 feet RVR). RVR values are displayed in 100 feet increments and are reported as follows:

1. 100−feet increments for products below 800 feet.

2. 200−feet increments for products between 800 feet and 3,000 feet.

3. 500−feet increments for products between 3,000 feet and 6,500 feet.

4. 25−meter increments for products below 150 meters.

5. 50−meter increments for products between 150 meters and 800 meters.

6. 100−meter increments for products between 800 meters and 1,200 meters.

7. 200−meter increments for products between 1,200 meters and 2,000 meters.

7−1−14. Reporting of Cloud Heights

a. Ceiling, by definition in the CFRs and as used in aviation weather reports and forecasts, is the height above

ground (or water) level of the lowest layer of clouds or obscuring phenomenon that is reported as “broken,”

“overcast,” or “obscuration,” e.g., an aerodrome forecast (TAF) which reads “BKN030” refers to height above

ground level. An area forecast which reads “BKN030” indicates that the height is above mean sea level.

REFERENCE−

AIM, Para 7−1−28, Key to Aerodrome Forecast (TAF) and Aviation Routine Weather Report (METAR), defines “broken,” “overcast,” and “obscuration.”

b. Pilots usually report height values above MSL, since they determine heights by the altimeter. This is taken

in account when disseminating and otherwise applying information received from pilots. (“Ceiling” heights are

always above ground level.) In reports disseminated as PIREPs, height references are given the same as received

from pilots, that is, above MSL.

c. In area forecasts or inflight advisories, ceilings are denoted by the contraction “CIG” when used with sky

cover symbols as in “LWRG TO CIG OVC005,” or the contraction “AGL” after, the forecast cloud height value.

Meteorology 7−1−43

AIM 2/20/25

When the cloud base is given in height above MSL, it is so indicated by the contraction “MSL” or “ASL”

following the height value. The heights of clouds tops, freezing level, icing, and turbulence are always given in

heights above ASL or MSL.

7−1−15. Reporting Prevailing Visibility

a. Surface (horizontal) visibility is reported in METAR reports in terms of statute miles and increments

3/ 5/ 3/ 1/ 5/thereof; e.g., 1/16, 1/8, 16, 1/4, 16, 8, 2, 8, 3/4, 7/8, 1, 1 1/8, etc. (Visibility reported by an unaugmented automated

site is reported differently than in a manual report, i.e., ASOS/AWOS: 0, 1/16, 1/8, 1/4, 1/2, 3/4, 1, 1 1/4, 1 1/2, 1 3/4, 2,

2 1/2, 3, 4, 5, etc., AWOS: M1/4, 1/4, 1/2, 3/4, 1, 1 1/4, 1 1/2, 1 3/4, 2, 2 1/2, 3, 4, 5, etc.) Visibility is determined through

the ability to see and identify preselected and prominent objects at a known distance from the usual point of

observation. Visibilities which are determined to be less than 7 miles, identify the obscuring atmospheric

condition; e.g., fog, haze, smoke, etc., or combinations thereof.

b. Prevailing visibility is the greatest visibility equaled or exceeded throughout at least one half of the horizon

circle, not necessarily contiguous. Segments of the horizon circle which may have a significantly different

visibility may be reported in the remarks section of the weather report; i.e., the southeastern quadrant of the

horizon circle may be determined to be 2 miles in mist while the remaining quadrants are determined to be 3 miles

in mist.

c. When the prevailing visibility at the usual point of observation, or at the tower level, is less than 4 miles,

certificated tower personnel will take visibility observations in addition to those taken at the usual point of

observation. The lower of these two values will be used as the prevailing visibility for aircraft operations.

7−1−16. Estimating Intensity of Rain and Ice Pellets

a. Rain

1. Light. From scattered drops that, regardless of duration, do not completely wet an exposed surface up

to a condition where individual drops are easily seen.

2. Moderate. Individual drops are not clearly identifiable; spray is observable just above pavements and

other hard surfaces.

3. Heavy. Rain seemingly falls in sheets; individual drops are not identifiable; heavy spray to height of

several inches is observed over hard surfaces.

b. Ice Pellets

1. Light. Scattered pellets that do not completely cover an exposed surface regardless of duration.

Visibility is not affected.

2. Moderate. Slow accumulation on ground. Visibility reduced by ice pellets to less than 7 statute miles.

3. Heavy. Rapid accumulation on ground. Visibility reduced by ice pellets to less than 3 statute miles.

7−1−17. Estimating Intensity of Snow or Drizzle (Based on Visibility)

a. Light. Visibility more than 1/2 statute mile.

b. Moderate. Visibility from more than 1/4 statute mile to 1/2 statute mile.

c. Heavy. Visibility 1/4 statute mile or less.

7−1−18. Pilot Weather Reports (PIREPs)

a. FAA air traffic facilities are required to solicit PIREPs when the following conditions are reported or

forecast: ceilings at or below 5,000 feet; visibility at or below 5 miles (surface or aloft); thunderstorms and related

phenomena; icing of light degree or greater; turbulence of moderate degree or greater; wind shear and reported

or forecast volcanic ash clouds.

7−1−44 Meteorology

2/20/25 AIM

b. Pilots are urged to cooperate and promptly volunteer reports of these conditions and other atmospheric data

such as: cloud bases, tops and layers; flight visibility; precipitation; visibility restrictions such as haze, smoke

and dust; wind at altitude; and temperature aloft.

c. PIREPs should be given to the ground facility with which communications are established; i.e., FSS,

ARTCC, or terminal ATC. One of the primary duties of the Inflight position is to serve as a collection point for

the exchange of PIREPs with en route aircraft.

d. If pilots are not able to make PIREPs by radio, reporting upon landing of the inflight conditions encountered

to the nearest FSS or Weather Forecast Office will be helpful. Some of the uses made of the reports are:

1. The A TCT uses the reports to expedite the flow of air traffic in the vicinity of the field and for hazardous

weather avoidance procedures.

2. The FSS uses the reports to brief other pilots, to provide inflight advisories, and weather avoidance

information to en route aircraft.

3. The ARTCC uses the reports to expedite the flow of en route traffic, to determine most favorable

altitudes, and to issue hazardous weather information within the center’s area.

4. The NWS uses the reports to verify or amend conditions contained in aviation forecast and advisories.

In some cases, pilot reports of hazardous conditions are the triggering mechanism for the issuance of advisories.

They also use the reports for pilot weather briefings.

5. The NWS, other government organizations, the military, and private industry groups use PIREPs for

research activities in the study of meteorological phenomena.

6. All air traffic facilities and the NWS forward the reports received from pilots into the weather distribution

system to assure the information is made available to all pilots and other interested parties.

e. The FAA, NWS, and other organizations that enter PIREPs into the weather reporting system use the format

listed in TBL 7−1−8. Items 1 through 6 are included in all transmitted PIREPs along with one or more of items

7 through 13. Although the PIREP should be as complete and concise as possible, pilots should not be overly

concerned with strict format or phraseology. The important thing is that the information is relayed so other pilots

may benefit from your observation. If a portion of the report needs clarification, the ground station will request

the information. Completed PIREPs will be transmitted to weather circuits as in the following examples:

EXAMPLE−

1. KCMH UA /OV APE 230010/TM 1516/FL085/TP BE20/SK BKN065/WX FV03SM HZ FU/TA 20/TB LGT

NOTE−

1. One zero miles southwest of Appleton VOR; time 1516 UTC; altitude eight thousand five hundred; aircraft type BE200;

bases of the broken cloud layer is six thousand five hundred; flight visibility 3 miles with haze and smoke; air temperature

20 degrees Celsius; light turbulence.

EXAMPLE−

2. KCRW UV /OV KBKW 360015 −KCRW/TM 1815/FL120//TP BE99/SK IMC/WX RA/TA M08 /WV 290030/TB

LGT−MDT/IC LGT RIME/RM MDT MXD ICG DURC KROA NWBND FL080−100 1750Z

NOTE−

2. From 15 miles north of Beckley VOR to Charleston VOR; time 1815 UTC; altitude 12,000 feet; type aircraft, BE−99; in

clouds; rain; temperature minus 8 Celsius; wind 290 degrees magnetic at 30 knots; light to moderate turbulence; light rime

icing during climb northwestbound from Roanoke, VA, between 8,000 and 10,000 feet at 1750 UTC.

f. For more detailed information on PIREPs, users can refer to the current version of the Aviation Weather

Handbook, FAA−H−8083−28.

Meteorology 7−1−45

AIM 2/20/25

TBL 7−1−8

PIREP Element Code Chart

PIREP ELEMENT PIREP CODE CONTENTS

1. 3−letter station identifier XXX Nearest weather reporting location to the reported phenomenon

2. Report type UA or UUA Routine or Urgent PIREP

3. Location /OV In relation to a VOR

4. Time /TM Coordinated Universal Time

5. Altitude /FL Essential for turbulence and icing reports

6. Type Aircraft /TP Essential for turbulence and icing reports

7. Sky cover /SK Cloud height and coverage (sky clear, few, scattered, broken, or

overcast)

8. Weather /WX Flight visibility, precipitation, restrictions to visibility, etc.

9. Temperature /TA Degrees Celsius

10. Wind /WV Direction in degrees magnetic north and speed in knots

11. Turbulence /TB See AIM paragraph 7−1−21

12. Icing /IC See AIM paragraph 7−1−19

13. Remarks /RM For reporting elements not included or to clarify previously

reported items

7−1−19. PIREPs Relating to Airframe Icing

a. The effects of ice on aircraft are cumulative-thrust is reduced, drag increases, lift lessens, and weight

increases. The results are an increase in stall speed and a deterioration of aircraft performance. In extreme cases,

2 to 3 inches of ice can form on the leading edge of the airfoil in less than 5 minutes. It takes but 1/2 inch of ice

to reduce the lifting power of some aircraft by 50 percent and increases the frictional drag by an equal percentage.

b. A pilot can expect icing when flying in visible precipitation, such as rain or cloud droplets, and the

temperature is between +02 and −10 degrees Celsius. When icing is detected, a pilot should do one of two things,

particularly if the aircraft is not equipped with deicing equipment; get out of the area of precipitation; or go to

an altitude where the temperature is above freezing. This “warmer” altitude may not always be a lower altitude.

Proper preflight action includes obtaining information on the freezing level and the above freezing levels in

precipitation areas. Report icing to ATC, and if operating IFR, request new routing or altitude if icing will be a

hazard. Be sure to give the type of aircraft to ATC when reporting icing. The following describes how to report

icing conditions.

1. Trace. Ice becomes noticeable. The rate of accumulation is slightly greater than the rate of sublimation.

A representative accretion rate for reference purposes is less than ¼ inch (6 mm) per hour on the outer wing. The

pilot should consider exiting the icing conditions before they become worse.

2. Light. The rate of ice accumulation requires occasional cycling of manual deicing systems to minimize

ice accretions on the airframe. A representative accretion rate for reference purposes is ¼ inch to 1 inch (0.6 to

2.5 cm) per hour on the unprotected part of the outer wing. The pilot should consider exiting the icing condition.

3. Moderate. The rate of ice accumulation requires frequent cycling of manual deicing systems to

minimize ice accretions on the airframe. A representative accretion rate for reference purposes is 1 to 3 inches

(2.5 to 7.5 cm) per hour on the unprotected part of the outer wing. The pilot should consider exiting the icing

condition as soon as possible.

4. Severe. The rate of ice accumulation is such that ice protection systems fail to remove the accumulation

of ice and ice accumulates in locations not normally prone to icing, such as areas aft of protected surfaces and

any other areas identified by the manufacturer. A representative accretion rate for reference purposes is more than

3 inches (7.5 cm) per hour on the unprotected part of the outer wing. By regulation, immediate exit is required.

7−1−46 Meteorology

2/20/25 AIM

NOTE−

Severe icing is aircraft dependent, as are the other categories of icing intensity. Severe icing may occur at any

ice accumulation rate when the icing rate or ice accumulations exceed the tolerance of the aircraft.

EXAMPLE−

Pilot report: give aircraft identification, location, time (UTC), intensity of type, altitude/FL, aircraft type, indicated air

speed (IAS), and outside air temperature (OAT).

NOTE−

1. Rime ice. Rough, milky, opaque ice formed by the instantaneous freezing of small supercooled water droplets.

2. Clear ice. A glossy, clear, or translucent ice formed by the relatively slow freezing of large supercooled water droplets.

3. The OAT should be requested by the FSS or ATC if not included in the PIREP .

7−1−20. Definitions of Inflight Icing Terms

See TBL 7−1−9, Icing Types, and TBL 7−1−10, Icing Conditions.

TBL 7−1−9

Icing Types

Clear Ice See Glaze Ice.

Glaze Ice Ice, sometimes clear and smooth, but usually containing some air pockets, which results in a

lumpy translucent appearance. Glaze ice results from supercooled drops/droplets striking a

surface but not freezing rapidly on contact. Glaze ice is denser, harder, and sometimes more

transparent than rime ice. Factors, which favor glaze formation, are those that favor slow

dissipation of the heat of fusion (i.e., slight supercooling and rapid accretion). With larger

accretions, the ice shape typically includes “horns” protruding from unprotected leading edge

surfaces. It is the ice shape, rather than the clarity or color of the ice, which is most likely to

be accurately assessed from the cockpit. The terms “clear” and “glaze” have been used for

essentially the same type of ice accretion, although some reserve “clear” for thinner accretions

which lack horns and conform to the airfoil.

Intercycle Ice Ice which accumulates on a protected surface between actuation cycles of a deicing system.

Known or Observed or

Detected Ice Accretion

Actual ice observed visually to be on the aircraft by the flight crew or identified by on−board

sensors.

Mixed Ice Simultaneous appearance or a combination of rime and glaze ice characteristics. Since the

clarity, color, and shape of the ice will be a mixture of rime and glaze characteristics, accurate

identification of mixed ice from the cockpit may be difficult.

Residual Ice Ice which remains on a protected surface immediately after the actuation of a deicing system.

Rime Ice A rough, milky, opaque ice formed by the rapid freezing of supercooled drops/droplets after

they strike the aircraft. The rapid freezing results in air being trapped, giving the ice its opaque

appearance and making it porous and brittle. Rime ice typically accretes along the stagnation

line of an airfoil and is more regular in shape and conformal to the airfoil than glaze ice. It is

the ice shape, rather than the clarity or color of the ice, which is most likely to be accurately

assessed from the cockpit.

Runback Ice Ice which forms from the freezing or refreezing of water leaving protected surfaces and

running back to unprotected surfaces.

Note−

Ice types are difficult for the pilot to discern and have uncertain effects on an airplane in flight. Ice type definitions will

be included in the AIM for use in the “Remarks” section of the PIREP and for use in forecasting.

Meteorology 7−1−47

AIM 2/20/25

TBL 7−1−10

Icing Conditions

Appendix C Icing Conditions Appendix C (14 CFR, part 25 and 29) is the certification icing condition standard

for approving ice protection provisions on aircraft. The conditions are specified in

terms of altitude, temperature, liquid water content (LWC), representative droplet

size (mean effective drop diameter [MED]), and cloud horizontal extent.

Forecast Icing Conditions Environmental conditions expected by a National Weather Service or an

FAA−approved weather provider to be conducive to the formation of inflight icing

on aircraft.

Freezing Drizzle (FZDZ) Drizzle is precipitation at ground level or aloft in the form of liquid water drops

which have diameters less than 0.5 mm and greater than 0.05 mm. Freezing drizzle

is drizzle that exists at air temperatures less than 0 C (supercooled), remains in

liquid form, and freezes upon contact with objects on the surface or airborne.

Freezing Precipitation Freezing precipitation is freezing rain or freezing drizzle falling through or outside

of visible cloud.

Freezing Rain (FZRA) Rain is precipitation at ground level or aloft in the form of liquid water drops which

have diameters greater than 0.5 mm. Freezing rain is rain that exists at air

temperatures less than 0C (supercooled), remains in liquid form, and freezes upon

contact with objects on the ground or in the air.

Icing in Cloud Icing occurring within visible cloud. Cloud droplets (diameter < 0.05 mm) will be

present; freezing drizzle and/or freezing rain may or may not be present.

Icing in Precipitation Icing occurring from an encounter with freezing precipitation, that is, supercooled

drops with diameters exceeding 0.05 mm, within or outside of visible cloud.

Known Icing Conditions Atmospheric conditions in which the formation of ice is observed or detected in

flight.

Note−

Because of the variability in space and time of atmospheric conditions, the existence

of a report of observed icing does not assure the presence or intensity of icing

conditions at a later time, nor can a report of no icing assure the absence of icing

conditions at a later time.

Potential Icing Conditions Atmospheric icing conditions that are typically defined by airframe manufacturers

relative to temperature and visible moisture that may result in aircraft ice accretion

on the ground or in flight. The potential icing conditions are typically defined in the

Airplane Flight Manual or in the Airplane Operation Manual.

Supercooled Drizzle Drops

(SCDD)

Synonymous with freezing drizzle aloft.

Supercooled Drops or /Droplets Water drops/droplets which remain unfrozen at temperatures below 0 C.

Supercooled drops are found in clouds, freezing drizzle, and freezing rain in the

atmosphere. These drops may impinge and freeze after contact on aircraft surfaces.

Supercooled Large Drops (SLD) Liquid droplets with diameters greater than 0.05 mm at temperatures less than

0C, i.e., freezing rain or freezing drizzle.

7−1−21. PIREPs Relating to Turbulence

a. When encountering turbulence, pilots are urgently requested to report such conditions to ATC as soon as

practicable. PIREPs relating to turbulence should state:

1. Aircraft location.

2. Time of occurrence in UTC.

3. Turbulence intensity.

4. Whether the turbulence occurred in or near clouds.

5. Aircraft altitude or flight level.

7−1−48 Meteorology

2/20/25 AIM

6. Type of aircraft.

7. Duration of turbulence.

EXAMPLE−

1. Over Omaha, 1232Z, moderate turbulence in clouds at Flight Level three one zero, Boeing 707.

2. From five zero miles south of Albuquerque to three zero miles north of Phoenix, 1250Z, occasional moderate chop at

Flight Level three three zero, DC8.

b. Duration and classification of intensity should be made using TBL 7−1−11.

TBL 7−1−11

Turbulence Reporting Criteria Table

Intensity Aircraft Reaction Reaction Inside Aircraft Reporting Term−Definition

Light Turbulence that momentarily causes

slight, erratic changes in altitude and/or

attitude (pitch, roll, yaw). Report as

Light Turbulence; 1

Turbulence that causes slight, rapid and

somewhat rhythmic bumpiness without

appreciable changes in altitude or

attitude. Report as Light Chop.

Occupants may feel a slight strain

against seat belts or shoulder straps.

Unsecured objects may be displaced

slightly. Food service may be con -

ducted and little or no difficulty is

encountered in walking.

Occasional−Less than 1/3 of the time.

Intermittent−1/3 to 2/3.

Continuous−More than 2/3.

Moderate Turbulence that is similar to Light

Turbulence but of greater intensity.

Changes in altitude and/or attitude occur

but the aircraft remains in positive

control at all times. It usually causes

variations in indicated airspeed. Report

as Moderate Turbulence; 1

Turbulence that is similar to Light Chop

but of greater intensity. It causes rapid

bumps or jolts without appreciable

changes in aircraft altitude or attitude.

Report as Moderate Chop.1

Occupants feel definite strains against

seat belts or shoulder straps. Unse -

cured objects are dislodged. Food

service and walking are difficult.

NOTE

1. Pilots should report location(s),

time (UTC), intensity, whether in or

near clouds, altitude, type of aircraft

and, when applicable, duration of

turbulence.

2. Duration may be based on time

between two locations or over a single

location. All locations should be

readily identifiable.

EXAMPLES:

a. Over Omaha. 1232Z, Moderate

Turbulence, in cloud, Flight

Level 310, B707.

b. From 50 miles south of Albuquer-

que to 30 miles north of Phoenix,

1210Z to 1250Z, occasional Moderate

Chop, Flight Level 330, DC8.

Severe Turbulence that causes large, abrupt

changes in altitude and/or attitude. It

usually causes large variations in

indicated airspeed. Aircraft may be

momentarily out of control. Report as

Severe Turbulence. 1

Occupants are forced violently against

seat belts or shoulder straps. Unse -

cured objects are tossed about. Food

Service and walking are impossible.

Extreme Turbulence in which the aircraft is

violently tossed about and is practically

impossible to control. It may cause

structural damage. Report as Extreme

Turbulence. 1

1 High level turbulence (normally above 15,000 feet ASL) not associated with cumuliform cloudiness, including thunderstorms,

should be reported as CAT (clear air turbulence) preceded by the appropriate intensity, or light or moderate chop.

7−1−22. Wind Shear PIREPs

a. Because unexpected changes in wind speed and direction can be hazardous to aircraft operations at low

altitudes on approach to and departing from airports, pilots are urged to promptly volunteer reports to controllers

of wind shear conditions they encounter. An advance warning of this information will assist other pilots in

avoiding or coping with a wind shear on approach or departure.

b. When describing conditions, use of the terms “negative” or “positive” wind shear should be avoided.

PIREPs of “negative wind shear on final,” intended to describe loss of airspeed and lift, have been interpreted

to mean that no wind shear was encountered. The recommended method for wind shear reporting is to state the

loss or gain of airspeed and the altitudes at which it was encountered.

Meteorology 7−1−49

AIM 2/20/25

EXAMPLE−

1. Denver Tower , Cessna 1234 encountered wind shear, loss of 20 knots at 400.

2. Tulsa Tower, American 721 encountered wind shear on final, gained 25 knots between 600 and 400 feet followed by loss

of 40 knots between 400 feet and surface.

1. Pilots who are not able to report wind shear in these specific terms are encouraged to make reports in

terms of the effect upon their aircraft.

EXAMPLE−

Miami Tower , Gulfstream 403 Charlie encountered an abrupt wind shear at 800 feet on final, max thrust required.

2. Pilots using Inertial Navigation Systems (INSs) should report the wind and altitude both above and below

the shear level.

c. Wind Shear Escape

1. Pilots should report to ATC when they are performing a wind shear escape maneuver. This report should

be made as soon as practicable, but not until aircraft safety and control is assured, which may not be satisfied

until the aircraft is clear of the wind shear or microburst. ATC should provide safety alerts and traffic advisories,

as appropriate.

EXAMPLE−

“Denver Tower , United 1154, wind shear escape.”

2. Once the pilot initiates a wind shear escape maneuver, ATC is not responsible for providing approved

separation between the aircraft and any other aircraft, airspace, terrain, or obstacle until the pilot reports that the

escape procedure is complete and approved separation has been re−established. Pilots should advise ATC that

they are resuming the previously assigned clearance or should request an alternate clearance.

EXAMPLE−

“Denver Tower , United ll54, wind shear escape complete, resuming last assigned heading/(name) DP/clearance.”

“Denver Tower , United ll54, wind shear escape complete, request further instructions.”

7−1−23. Clear Air Turbulence (CAT) PIREPs

CAT has become a very serious operational factor to flight operations at all levels and especially to jet traffic

flying in excess of 15,000 feet. The best available information on this phenomenon must come from pilots via

the PIREP reporting procedures. All pilots encountering CAT conditions are urgently requested to report time,

location, and intensity (light, moderate, severe, or extreme) of the element to the FAA facility with which they

are maintaining radio contact. If time and conditions permit, elements should be reported according to the

standards for other PIREPs and position reports.

REFERENCE−

AIM, Para 7−1−21, PIREPs Relating to Turbulence.

7−1−24. Microbursts

a. Relatively recent meteorological studies have c onfirmed the existence of microburst phenomenon.

Microbursts are small scale intense downdrafts which, on reaching the surface, spread outward in all directions

from the downdraft center. This causes the presence of both vertical and horizontal wind shears that can be

extremely hazardous to all types and categories of aircraft, especially at low altitudes. Due to their small size,

short life span, and the fact that they can occur over areas without surface precipitation, microbursts are not easily

detectable using conventional weather radar or wind shear alert systems.

b. Parent clouds producing microburst activity can be any of the low or middle layer convective cloud types.

Note, however, that microbursts commonly occur within the heavy rain portion of thunderstorms, and in much

weaker, benign appearing convective cells that have little or no precipitation reaching the ground.

7−1−50 Meteorology

e T

2/20/25 AIM

FIG 7−1−13

Evolution of a Microburst

Meteorology

HEIGHT (feet)

10,00010,000

5,0005,000

et)

WIND SPEEDWIND SPEED

10-20 knots10-20 knots

> 20 knots> 20 knots

T-5 Min T-2 Min T T + 5 MinT + 5 MinT-5 Min T-2 Min T + 10 MinT + 10 Min

0 1 2

SCALE (miles)SCALE (miles)

Vertical cross section of the evolution of a microburst wind field. T is the time of initial divergence at

the surface. The shading refers to the vector wind speeds. Figure adapted from Wilson et al., 1984,

Microburst Wind Structure and Evaluation of Doppler Radar for Wind Shear Detection, DOT/FAA

Report No. DOT/FAA/PM-84/29, National Technical Information Service, Springfield, VA 37 pp.

c. The life cycle of a microburst as it descends in a convective rain shaft is seen in FIG 7−1−13. An important

consideration for pilots is the fact that the microburst intensifies for about 5 minutes after it strikes the ground.

d. Characteristics of microbursts include:

1. Size. The microburst downdraft is typically less than 1 mile in diameter as it descends from the cloud

base to about 1,000−3,000 feet above the ground. In the transition zone near the ground, the downdraft changes

to a horizontal outflow that can extend to approximately 2 1/2 miles in diameter.

2. Intensity. The downdrafts can be as strong as 6,000 feet per minute. Horizontal winds near the surface

can be as strong as 45 knots resulting in a 90 knot shear (headwind to tailwind change for a traversing aircraft)

across the microburst. These strong horizontal winds occur within a few hundred feet of the ground.

3. Visual Signs. Microbursts can be found almost anywhere that there is convective activity. They may be

embedded in heavy rain associated with a thunderstorm or in light rain in benign appearing virga. When there

is little or no precipitation at the surface accompanying the microburst, a ring of blowing dust may be the only

visual clue of its existence.

4. Duration. An individual microburst will seldom last longer than 15 minutes from the time it strikes the

ground until dissipation. The horizontal winds continue to increase during the first 5 minutes with the maximum

intensity winds lasting approximately 2−4 minutes. Sometimes microbursts are concentrated into a line structure,

and under these conditions, activity may continue for as long as an hour. Once microburst activity starts, multiple

microbursts in the same general area are not uncommon and should be expected.

7−1−51

AIM 2/20/25

FIG 7−1−14

Microburst Encounter During Takeoff

A microburst encounter during takeoff. The airplane first encounters a headwind and experiences increasing

performance (1), this is followed in short succession by a decreasing headwind component (2), a downdraft

(3), and finally a strong tailwind (4), where 2 through 5 all result in decreasing performance of the airplane.

Position (5) represents an extreme situation just prior to impact. Figure courtesy of Walter Frost, FWG

Associates, Inc., Tullahoma, Tennessee.

e. Microburst wind shear may create a severe hazard for aircraft within 1,000 feet of the ground, particularly

during the approach to landing and landing and take-off phases. The impact of a microburst on aircraft which

have the unfortunate experience of penetrating one is characterized in FIG 7−1−14. The aircraft may encounter

a headwind (performance increasing) followed by a downdraft and tailwind (both performance decreasing),

possibly resulting in terrain impact.

Meteorology7−1−52

2/20/25 AIM

FIG 7−1−15

NAS Wind Shear Product Systems

f. Detection of Microbursts, Wind Shear and Gust Fronts.

1. FAA’s Integrated Wind Shear Detection Plan.

(a) The FAA currently employs an integrated plan for wind shear detection that will significantly improve

both the safety and capacity of the majority of the airports currently served by the air carriers. This plan integrates

several programs, such as the Integrated Terminal Weather System (ITWS), Terminal Doppler Weather Radar

(TDWR), Weather Systems Processor (WSP), and Low Level Wind Shear Alert Systems (LLWAS) into a single

strategic concept that significantly improves the aviation weather information in the terminal area. (See

FIG 7−1−15.)

(b) The wind shear/microburst information and warnings are displayed on the ribbon display terminals

(RBDT) located in the tower cabs. They are identical (and standardized) in the LLWAS, TDWR and WSP

systems, and so designed that the controller does not need to interpret the data, but simply read the displayed

information to the pilot. The RBDTs are constantly monitored by the controller to ensure the rapid and timely

dissemination of any hazardous event(s) to the pilot.

Meteorology 7−1−53

AIM 2/20/25

FIG 7−1−16

LLWAS Siting Criteria

aircraft on approach or departure, will alert the pilot/crew to the potential of, and to be prepared for, a situation

that could become very dangerous! Without these warnings, the aircraft may NOT be able to climb out of, or

safely transition, the event, resulting in a catastrophe. The air carriers, working with the FAA, have developed

specialized training programs using their simulators to train and prepare their pilots on the demanding aircraft

procedures required to escape these very dangerous wind shear and/or microburst encounters.

2. Low Level Wind Shear Alert System (LLWAS).

(a) The LLWAS provides wind data and software processes to detect the presence of hazardous wind

shear and microbursts in the vicinity of an airport. Wind sensors, mounted on poles sometimes as high as 150

feet, are (ideally) located 2,000 − 3,500 feet, but not more than 5,000 feet, from the centerline of the runway. (See

FIG 7−1−16.)

7−1−54 Meteorology

2/20/25 AIM

FIG 7−1−17

Warning Boxes

(b) LLWAS was fielded in 1988 at 110 airports across the nation. Many of these systems have been

replaced by new TDWR and WSP technology. While all legacy LLWAS systems will eventually be phased out,

39 airports will be upgraded to LLWAS−NE (Network Expansion) system. The new LLWAS−NE systems not

only provide the controller with wind shear warnings and alerts, including wind shear/microburst detection at

the airport wind sensor location, but also provide the location of the hazards relative to the airport runway(s).

It also has the flexibility and capability to grow with the airport as new runways are built. As many as 32 sensors,

strategically located around the airport and in relationship to its runway configuration, can be accommodated

by the LLWAS−NE network.

3. Terminal Doppler Weather Radar (TDWR).

(a) TDWRs have been deployed at 45 locations across the U.S. Optimum locations for TDWRs are 8 to

12 miles off of the airport proper, and designed to look at the airspace around and over the airport to detect

microbursts, gust fronts, wind shifts, and precipitation intensities. TDWR products advise the controller of wind

shear and microburst events impacting all runways and the areas 1/2 mile on either side of the extended centerline

of the runways out to 3 miles on final approach and 2 miles out on departure. (FIG 7−1−17 is a theoretical view

of the warning boxes, including the runway, that the software uses in determining the location(s) of wind shear

or microbursts). These warnings are displayed (as depicted in the examples in subparagraph 5) on the RBDT.

(b) It is very important to understand what TDWR does NOT DO:

(1) It DOES NOT warn of wind shear outside of the alert boxes (on the arrival and departure ends of

the runways);

(2) It DOES NOT detect wind shear that is NOT a microburst or a gust front;

(3) It DOES NOT detect gusty or cross wind conditions; and

(4) It DOES NOT detect turbulence.

However, research and development is continuing on these systems. Future improvements may include such

areas as storm motion (movement), improved gust front detection, storm growth and decay, microburst

prediction, and turbulence detection.

Meteorology 7−1−55

AIM 2/20/25

specialists for planning purposes. The GSD displays (in color) 6 levels of weather (precipitation), gust fronts and

predicted storm movement(s). This data is used by the tower supervisor(s), traffic management specialists and

controllers to plan for runway changes and arrival/departure route changes in order to both reduce aircraft delays

and increase airport capacity.

4. Weather Systems Processor (WSP).

(a) The WSP provides the controller, supervisor, traffic management specialist, and ultimately the pilot,

with the same products as the terminal doppler weather radar (TDWR) at a fraction of the cost of a TDWR. This

is accomplished by utilizing new technologies to access the weather channel capabilities of the existing ASR−9

radar located on or near the airport, thus eliminating the requirements for a separate radar location, land

acquisition, support facilities and the associated communication landlines and expenses.

(b) The WSP utilizes the same RBDT display as the TDWR and LLWAS, and, just like TDWR, also has

a GSD for planning purposes by supervisors, traffic management specialists and controllers. The WSP GSD

emulates the TDWR display, i.e., it also depicts 6 levels of precipitation, gust fronts and predicted storm

movement, and like the TDWR GSD, is used to plan for runway changes and arrival/departure route changes

in order to reduce aircraft delays and to increase airport capacity.

5. Operational aspects of LLWAS, TDWR and WSP.

To demonstrate how this data is used by both the controller and the pilot, 3 ribbon display examples and their

explanations are presented:

(a) MICROBURST ALERTS

EXAMPLE−

This is what the controller sees on his/her ribbon display in the tower cab.

27A MBA 35K− 2MF 250 20

NOTE−

(See FIG 7−1−18 to see how the TDWR/WSP determines the microburst location).

This is what the controller will say when issuing the alert.

PHRASEOLOGY−

RUNWAY 27 ARRIVAL, MICROBURST ALERT, 35 KT LOSS 2 MILE FINAL, THRESHOLD WIND 250 AT 20.

In plain language, the controller is telling the pilot that on approach to runway 27, there is a microburst alert on

the approach lane to the runway, and to anticipate or expect a 35 knot loss of airspeed at approximately 2 miles

out on final approach (where it will first encounter the phenomena). With that information, the aircrew is

forewarned, and should be prepared to apply wind shear/microburst escape procedures should they decide to

continue the approach. Additionally, the surface winds at the airport for landing runway 27 are reported as

250 degrees at 20 knots.

NOTE−

Threshold wind is at pilot’ s request or as deemed appropriate by the controller .

REFERENCE−

F AA Order JO 7110.65, Para 3−1−8b2(a), Air Traffic Control, Low Level Wind Shear/Microburst Advisories.

Meteorology7−1−56

2/20/25 AIM

FIG 7−1−18

Microburst Alert

(b) WIND SHEAR ALERTS

EXAMPLE−

This is what the controller sees on his/her ribbon display in the tower cab.

27A WSA 20K− 3MF 200 15

NOTE−

(See FIG 7−1−19 to see how the TDWR/WSP determines the wind shear location).

This is what the controller will say when issuing the alert.

PHRASEOLOGY−

RUNWAY 27 ARRIVAL, WIND SHEAR ALERT, 20 KT LOSS 3 MILE FINAL, THRESHOLD WIND 200 AT 15.

In plain language, the controller is advising the aircraft arriving on runway 27 that at about 3 miles out they can

expect to encounter a wind shear condition that will decrease their airspeed by 20 knots and possibly encounter

turbulence. Additionally, the airport surface winds for landing runway 27 are reported as 200 degrees at 15 knots.

NOTE−

Threshold wind is at pilot’ s request or as deemed appropriate by the controller .

REFERENCE−

F AA Order JO 7110.65, Para 3−1−8, Low Level Wind Shear/Microburst Advisories, Subpara b2(a).

Meteorology 7−1−57

AIM 2/20/25

FIG 7−1−19

Weak Microburst Alert

7−1−58 Meteorology

2/20/25 AIM

FIG 7−1−20

Gust Front Alert

EXAMPLE−

This is what the controller sees on his/her ribbon display in the tower cab.

27A WSA 20K+ RWY 250 20

27D WSA 20K+ RWY 250 20

NOTE−

(See FIG 7−1−20 to see how the TDWR/WSP determines the gust front/wind shear location.)

This is what the controller will say when issuing the alert.

PHRASEOLOGY−

MULTIPLE WIND SHEAR ALERTS. RUNWAY 27 ARRIVAL, WIND SHEAR ALERT, 20 KT GAIN ON RUNWAY; RUNWAY

27 DEP ARTURE, WIND SHEAR ALERT, 20 KT GAIN ON RUNWAY, WIND 250 AT 20.

EXAMPLE−

In this example, the controller is advising arriving and departing aircraft that they could encounter a wind shear condition

right on the runway due to a gust front (significant change of wind direction) with the possibility of a 20 knot gain in airspeed

associated with the gust front. Additionally, the airport surface winds (for the runway in use) are reported as 250 degrees

at 20 knots.

REFERENCE−

F AA Order 7110.65, Para 3−1−8, Low Level Wind Shear/Microburst Advisories, Subpara b2(d).

6. The Terminal Weather Information for Pilots System (TWIP).

(a) With the increase in the quantity and quality of terminal weather information available through

TDWR, the next step is to provide this information directly to pilots rather than relying on voice communications

Meteorology 7−1−59

FAA Aeronautical Information Manual: Chapter 3 — Chapter 3 — Part 5

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