Goniometer. As used in radio frequency (RF) antenna
systems, a direction-sensing device consisting of two fixed
loops of wire oriented 90° from each other, which separately
sense received signal strength and send those signals to two
rotors (also oriented 90°) in the sealed direction-indicating
instrument. The rotors are attached to the direction-indicating
needle of the instrument and rotated by a small motor until
minimum magnetic field is sensed near the rotors.
GPS. See global positioning system.
GPS Approach Overlay Program. An authorization for
pilots to use GPS avionics under IFR for flying designated
existing nonprecision instrument approach procedures, with
the exception of LOC, LDA, and SDF procedures.
Graveyard spiral. The illusion of the cessation of a turn
while still in a prolonged, coordinated, constant rate turn,
which can lead a disoriented pilot to a loss of control of the
aircraft.
Great circle route. The shortest distance across the surface
of a sphere (the Earth) between two points on the surface.
Ground proximity warning system (GPWS). A system
designed to determine an aircraft’s clearance above the Earth
and provides limited predictability about aircraft position
relative to rising terrain.
Groundspeed. Speed over the ground, either closing speed to
the station or waypoint, or speed over the ground in whatever
direction the aircraft is going at the moment, depending upon
the navigation system used.
GS. See glide slope.
GWPS. See ground proximity warning system.
HAA. See height above airport.
HAL. See height above landing.
HAT. See height above touchdown elevation.
Hazardous attitudes. Five aeronautical decision-making
attitudes that may contribute to poor pilot judgment:
antiauthority, impulsivity, invulnerability, machismo, and
resignation.
Hazardous Inflight Weather Advisory Service (HIWAS).
Service providing recorded weather forecasts broadcast to
airborne pilots over selected VORs.
Head-up display (HUD). A special type of flight viewing
screen that allows the pilot to watch the flight instruments
and other data while looking through the windshield of the
aircraft for other traffic, the approach lights, or the runway.
Height above airport (HAA). The height of the MDA above
the published airport elevation.
Height above landing (HAL). The height above a designated
helicopter landing area used for helicopter instrument
approach procedures.
Height above touchdown elevation (HAT). The DA/DH or
MDA above the highest runway elevation in the touchdown
zone (first 3,000 feet of the runway).
HF. High frequency.
Hg. Abbreviation for mercury, from the Latin
hydrargyrum.
HIWAS. See Hazardous Inflight Weather Advisory
Service.
Holding. A predetermined maneuver that keeps aircraft
within a specified airspace while awaiting further clearance
from ATC.
Holding pattern. A racetrack pattern, involving two turns
and two legs, used to keep an aircraft within a prescribed
airspace with respect to a geographic fix. A standard pattern
uses right turns; nonstandard patterns use left turns.
Homing. Flying the aircraft on any heading required to keep
the needle pointing to the 0° relative bearing position.
Horizontal situation indicator (HSI). A flight navigation
instrument that combines the heading indicator with a CDI,
in order to provide the pilot with better situational awareness
of location with respect to the courseline.
HSI. See horizontal situation indicator.
HUD. See head-up display.
Human factors. A multidisciplinary field encompassing the
behavioral and social sciences, engineering, and physiology,
to consider the variables that influence individual and
crew performance for the purpose of optimizing human
performance and reducing errors.
Hypoxia. A state of oxygen deficiency in the body sufficient
to impair functions of the brain and other organs.
IAF. See initial approach fix.
IAP. See instrument approach procedures.
IAS. See indicated airspeed.
ICAO. See International Civil Aviation Organization.
Ident. Air Traffic Control request for a pilot to push
the button on the transponder to identify return on the
controller’s scope.
IFR. See instrument flight rules.
ILS. See instrument landing system.
ILS categories. Categories of instrument approach
procedures allowed at airports equipped with the following
types of instrument landing systems:
ILS Category I: Provides for approach to a height
above touchdown of not less than 200 feet, and with
runway visual range of not less than 1,800 feet.
ILS Category II: Provides for approach to a height
above touchdown of not less than 100 feet and with
runway visual range of not less than 1,200 feet.
ILS Category IIIA: Provides for approach without
a decision height minimum and with runway visual
range of not less than 700 feet.
ILS Category IIIB: Provides for approach without
a decision height minimum and with runway visual
range of not less than 150 feet.
ILS Category IIIC: Provides for approach without a
decision height minimum and without runway visual
range minimum.
IMC. See instrument meteorological conditions.
Indicated airspeed (IAS). Shown on the dial of the
instrument airspeed indicator on an aircraft. Directly related
to calibrated airspeed (CAS), IAS includes instrument errors
and position error.
Indirect indication. A reflection of aircraft pitch-and-bank
attitude by the instruments other than the attitude indicator.
Induced drag. Drag caused by the same factors that produce
lift; its amount varies inversely with airspeed. As airspeed
decreases, the angle of attack must increase, in turn increasing
induced drag.
Induction icing. A type of ice in the induction system that
reduces the amount of air available for combustion. The most
commonly found induction icing is carburetor icing.
Inertial navigation system (INS). A computer-based
navigation system that tracks the movement of an aircraft
via signals produced by onboard accelerometers. The initial
location of the aircraft is entered into the computer, and all
subsequent movement of the aircraft is sensed and used to
keep the position updated. An INS does not require any inputs
from outside signals.
Initial approach fix (IAF). The fix depicted on IAP charts
where the instrument approach procedure (IAP) begins unless
otherwise authorized by ATC.
Inoperative components. Higher minimums are prescribed
when the specified visual aids are not functioning; this
information is listed in the Inoperative Components Table found
in the United States Terminal Procedures Publications.
INS. See inertial navigation system.
Instantaneous vertical speed indicator (IVSI). Assists in
interpretation by instantaneously indicating the rate of climb
or descent at a given moment with little or no lag as displayed
in a vertical speed indicator (VSI).
Instrument approach procedures (IAP). A series of
predetermined maneuvers for the orderly transfer of an
aircraft under IFR from the beginning of the initial approach
to a landing or to a point from which a landing may be
made visually.
Instrument flight rules (IFR). Rules and regulations
established by the Federal Aviation Administration to govern
flight under conditions in which flight by outside visual
reference is not safe. IFR flight depends upon flying by
reference to instruments in the flight deck, and navigation is
accomplished by reference to electronic signals.
Instrument landing system (ILS). An electronic system
that provides both horizontal and vertical guidance to a
specific runway, used to execute a precision instrument
approach procedure.
Instrument meteorological conditions (IMC).
Meteorological conditions expressed in terms of visibility,
distance from clouds, and ceiling less than the minimums
specified for visual meteorological conditions, requiring
operations to be conducted under IFR.
Instrument takeoff. Using the instruments rather than
outside visual cues to maintain runway heading and execute
a safe takeoff.
Interference drag. Drag generated by the collision of
airstreams creating eddy currents, turbulence, or restrictions
to smooth flow.
International Civil Aviation Organization (ICAO). The
United Nations agency for developing the principles and
techniques of international air navigation, and fostering planning
and development of international civil air transport.
International standard atmosphere (IAS). A model of
standard variation of pressure and temperature.
Inversion illusion. The feeling that the aircraft is tumbling
backwards, caused by an abrupt change from climb to straight-
and-level flight while in situations lacking visual reference.
Inverter. A solid-state electronic device that converts D.C.
into A.C. current of the proper voltage and frequency to
operate A.C. gyro instruments.
Isogonic lines. Lines drawn across aeronautical charts to
connect points having the same magnetic variation.
IVSI. See instantaneous vertical speed indicator.
Jet route. A route designated to serve flight operations from
18,000 feet MSL up to and including FL 450.
Jet stream. A high-velocity narrow stream of winds, usually
found near the upper limit of the troposphere, which flows
generally from west to east.
KIAS. Knots indicated airspeed.
Kollsman window. A barometric scale window of a
sensitive altimeter used to adjust the altitude for the
altimeter setting.
LAAS. See local area augmentation system.
Lag. The delay that occurs before an instrument needle attains
a stable indication.
Land as soon as possible. ATC instruction to pilot. Land
without delay at the nearest suitable area, such as an open
field, at which a safe approach and landing is assured.
Land as soon as practical. ATC instruction to pilot. The
landing site and duration of flight are at the discretion of the
pilot. Extended flight beyond the nearest approved landing
area is not recommended.
Land immediately. ATC instruction to pilot. The urgency
of the landing is paramount. The primary consideration is
to ensure the survival of the occupants. Landing in trees,
water, or other unsafe areas should be considered only as
a last resort.
LDA. See localizer-type directional aid.
Lead radial. The radial at which the turn from the DME arc
to the inbound course is started.
Leans, the. A physical sensation caused by an abrupt
correction of a banked attitude entered too slowly to
stimulate the motion sensing system in the inner ear. The
abrupt correction can create the illusion of banking in the
opposite direction.
Lift. A component of the total aerodynamic force on an airfoil
and acts perpendicular to the relative wind.
Lines of flux. Invisible lines of magnetic force passing
between the poles of a magnet.
L/MF. See low or medium frequency.
LMM. See locator middle marker.
Load factor. The ratio of a specified load to the total weight
of the aircraft. The specified load is expressed in terms of
any of the following: aerodynamic forces, inertial forces, or
ground or water reactions.
Loadmeter. A type of ammeter installed between the generator
output and the main bus in an aircraft electrical system.
LOC. See localizer.
Local area augmentation system (LAAS). A differential
global positioning system (DGPS) that improves the accuracy
of the system by determining position error from the GPS
satellites, then transmitting the error, or corrective factors,
to the airborne GPS receiver.
Localizer (LOC). The portion of an ILS that gives left/right
guidance information down the centerline of the instrument
runway for final approach.
Localizer-type directional aid (LDA). A NAVAID used
for nonprecision instrument approaches with utility and
accuracy comparable to a localizer but which is not a part
of a complete ILS and is not aligned with the runway. Some
LDAs are equipped with a glide slope.
Locator middle marker (LMM). Nondirectional radio
beacon (NDB) compass locator, collocated with a middle
marker (MM).
Locator outer marker (LOM). NDB compass locator,
collocated with an outer marker (OM).
LOM. See locator outer marker.
Long range navigation (LORAN). An electronic
navigational system by which hyperbolic lines of position
are determined by measuring the difference in the time of
reception of synchronized pulse signals from two fixed
transmitters. LORAN A operates in the 1750 to 1950 kHz
frequency band. LORAN C and D operate in the 100 to 110
kHz frequency band.
LORAN. See long range navigation.
Low or medium frequency. A frequency range between
190–535 kHz with the medium frequency above 300
kHz. Generally associated with nondirectional beacons
transmitting a continuous carrier with either a 400 or 1,020
Hz modulation.
Lubber line. The reference line used in a magnetic compass
or heading indicator.
MAA. See maximum authorized altitude.
Mach number. The ratio of the true airspeed of the aircraft
to the speed of sound in the same atmospheric conditions,
named in honor of Ernst Mach, late 19th century physicist.
Mach meter. The instrument that displays the ratio of the
speed of sound to the true airspeed an aircraft is flying.
Magnetic bearing (MB). The direction to or from a radio
transmitting station measured relative to magnetic north.
Magnetic heading (MH). The direction an aircraft is pointed
with respect to magnetic north.
Mandatory altitude. An altitude depicted on an instrument
approach chart with the altitude value both underscored and
overscored. Aircraft are required to maintain altitude at the
depicted value.
Mandatory block altitude. An altitude depicted on an
instrument approach chart with two underscored and
overscored altitude values between which aircraft are
required to maintain altitude.
MAP. See missed approach point.
Margin identification. The top and bottom areas on an
instrument approach chart that depict information about
the procedure, including airport location and procedure
identification.
Marker beacon. A low-powered transmitter that directs its
signal upward in a small, fan-shaped pattern. Used along the
flight path when approaching an airport for landing, marker
beacons indicate both aurally and visually when the aircraft
is directly over the facility.
Maximum altitude. An altitude depicted on an instrument
approach chart with overscored altitude value at which or
below aircraft are required to maintain altitude.
Maximum authorized altitude (MAA). A published altitude
representing the maximum usable altitude or flight level for
an airspace structure or route segment.
MB. See magnetic bearing.
MCA. See minimum crossing altitude.
MDA. See minimum descent altitude.
MEA. See minimum en route altitude.
Mean sea level. The average height of the surface of the
sea at a particular location for all stages of the tide over a
19-year period.
MFD. See multi-function display.
MH. See magnetic heading.
MHz. Megahertz.
Microwave landing system (MLS). A precision instrument
approach system operating in the microwave spectrum which
normally consists of an azimuth station, elevation station,
and precision distance measuring equipment.
Mileage breakdown. A fix indicating a course change
that appears on the chart as an “x” at a break between two
segments of a federal airway.
Military operations area (MOA). Airspace established for
the purpose of separating certain military training activities
from IFR traffic.
Military training route (MTR). Airspace of defined vertical
and lateral dimensions established for the conduct of military
training at airspeeds in excess of 250 knots indicated airspeed
(KIAS).
Minimum altitude. An altitude depicted on an instrument
approach chart with the altitude value underscored. Aircraft are
required to maintain altitude at or above the depicted value.
Minimum crossing altitude (MCA). The lowest allowed
altitude at certain fixes an aircraft must cross when proceeding
in the direction of a higher minimum en route altitude
(MEA).
Minimum descent altitude (MDA). The lowest altitude (in
feet MSL) to which descent is authorized on final approach,
or during circle-to-land maneuvering in execution of a
nonprecision approach.
Minimum en route altitude (MEA). The lowest published
altitude between radio fixes that ensures acceptable
navigational signal coverage and meets obstacle clearance
requirements between those fixes.
Minimum obstruction clearance altitude (MOCA). The
lowest published altitude in effect between radio fixes on VOR
airways, off-airway routes, or route segments, which meets
obstacle clearance requirements for the entire route segment
and which ensures acceptable navigational signal coverage
only within 25 statute (22 nautical) miles of a VOR.
Minimum reception altitude (MRA). The lowest altitude
at which an airway intersection can be determined.
Minimum safe altitude (MSA). The minimum altitude
depicted on approach charts which provides at least 1,000 feet
of obstacle clearance for emergency use within a specified
distance from the listed navigation facility.
Minimum vectoring altitude (MVA). An IFR altitude lower
than the minimum en route altitude (MEA) that provides
terrain and obstacle clearance.
Minimums section. The area on an IAP chart that displays the
lowest altitude and visibility requirements for the approach.
Missed approach. A maneuver conducted by a pilot when an
instrument approach cannot be completed to a landing.
Missed approach point (MAP). A point prescribed in each
instrument approach at which a missed approach procedure
shall be executed if the required visual reference has not
been established.
Mixed ice. A mixture of clear ice and rime ice.
MLS. See microwave landing system.
MM. Middle marker.
MOA. See military operations area.
MOCA. See minimum obstruction clearance altitude.
Mode C. Altitude reporting transponder mode.
MRA. See minimum reception altitude.
MSA. See minimum safe altitude.
MSL. See mean sea level.
MTR. See military training route.
Multi-function display (MFD). Small screen (CRT or LCD)
in an aircraft that can be used to display information to the
pilot in numerous configurable ways. Often an MFD will be
used in concert with a Primary Flight Display.
MVA. See minimum vectoring altitude.
NACG. See National Aeronautical Charting Group.
NAS. See National Airspace System.
National Airspace System (NAS). The common network of
United States airspace—air navigation facilities, equipment
and services, airports or landing areas; aeronautical charts,
information and services; rules, regulations and procedures,
technical information; and manpower and material.
National Aeronautical Charting Group (NACG). A
Federal agency operating under the FAA, responsible for
publishing charts such as the terminal procedures and en
route charts.
National Route Program (NRP). A set of rules and
procedures designed to increase the flexibility of user flight
planning within published guidelines.
National Security Area (NSA). Areas consisting of airspace of
defined vertical and lateral dimensions established at locations
where there is a requirement for increased security and safety
of ground facilities. Pilots are requested to voluntarily avoid
flying through the depicted NSA. When it is necessary to
provide a greater level of security and safety, flight in NSAs
may be temporarily prohibited. Regulatory prohibitions are
disseminated via NOTAMs.
National Transportation Safety Board (NTSB). A United
States Government independent organization responsible for
investigations of accidents involving aviation, highways,
waterways, pipelines, and railroads in the United States.
NTSB is charged by congress to investigate every civil
aviation accident in the United States.
NAVAID. Naviagtional aid.
NAV/COM. Navigation and communication radio.
NDB. See nondirectional radio beacon.
NM. Nautical mile.
NOAA. National Oceanic and Atmospheric Administration.
No-gyro approach. A radar approach that may be used in
case of a malfunctioning gyro-compass or directional gyro.
Instead of providing the pilot with headings to be flown,
the controller observes the radar track and issues control
instructions “turn right/left” or “stop turn,” as appropriate.
Nondirectional radio beacon (NDB). A ground-based radio
transmitter that transmits radio energy in all directions.
Nonprecision approach. A standard instrument approach
procedure in which only horizontal guidance is provided.
No procedure turn (NoPT). Term used with the appropriate
course and altitude to denote that the procedure turn is not
required.
NoPT. See no procedure turn.
Notice to Airmen (NOTAM). A notice filed with an aviation
authority to alert aircraft pilots of any hazards en route or at
a specific location. The authority in turn provides means of
disseminating relevant NOTAMs to pilots.
NRP. See National Route Program.
NSA. See National Security Area.
NTSB. See National Transportation Safety Board.
NWS. National Weather Service.
Obstacle departure procedures (ODP). Obstacle clearance
protection provided to aircraft in instrument meteorological
conditions (IMC).
ODP. See obstacle departure procedures.
OM. Outer marker.
Omission error. The failure to anticipate significant
instrument indications following attitude changes; for
example, concentrating on pitch control while forgetting
about heading or roll information, resulting in erratic control
of heading and bank.
Optical illusion. A misleading visual image. For the
purpose of this handbook, the term refers to the brain’s
misinterpretation of features on the ground associated
with landing, which causes a pilot to misread the spatial
relationships between the aircraft and the runway.
Orientation. Awareness of the position of the aircraft and
of oneself in relation to a specific reference point.
Otolith organ. An inner ear organ that detects linear
acceleration and gravity orientation.
Outer marker. A marker beacon at or near the glide slope
intercept altitude of an ILS approach. It is normally located
four to seven miles from the runway threshold on the
extended centerline of the runway.
Overcontrolling. Using more movement in the control
column than is necessary to achieve the desired pitch-and
bank condition.
Overpower. To use more power than required for the purpose
of achieving a faster rate of airspeed change.
P-static. See precipitation static.
PAPI. See precision approach path indicator.
PAR. See precision approach radar.
Parasite drag. Drag caused by the friction of air moving
over the aircraft structure; its amount varies directly with
the airspeed.
PFD. See primary flight display.
PIC. See pilot-in-command.
Pilot-in-command (PIC). The pilot responsible for the
operation and safety of an aircraft.
Pilot report (PIREP). Report of meteorological phenomena
encountered by aircraft.
Pilot’s Operating Handbook/Airplane Flight Manual
(POH/AFM). FAA-approved documents published by the
airframe manufacturer that list the operating conditions for
a particular model of aircraft.
PIREP. See pilot report.
Pitot pressure. Ram air pressure used to measure airspeed.
Pitot-static head. A combination pickup used to sample pitot
pressure and static air pressure.
Plan view. The overhead view of an approach procedure on
an instrument approach chart. The plan view depicts the routes
that guide the pilot from the en route segments to the IAF.
POH/AFM. See Pilot’s Operating Handbook/Airplane
Flight Manual.
Point-in-space approach. A type of helicopter instrument
approach procedure to a missed approach point more than
2,600 feet from an associated helicopter landing area.
Position error. Error in the indication of the altimeter, ASI,
and VSI caused by the air at the static system entrance not
being absolutely still.
Position report. A report over a known location as
transmitted by an aircraft to ATC.
Precession. The characteristic of a gyroscope that causes an
applied force to be felt, not at the point of application, but
90° from that point in the direction of rotation.
Precipitation static (P-static). A form of radio interference
caused by rain, snow, or dust particles hitting the antenna and
inducing a small radio-frequency voltage into it.
Precision approach. A standard instrument approach
procedure in which both vertical and horizontal guidance
is provided.
Precision approach path indicator (PAPI). A system of
lights similar to the VASI, but consisting of one row of lights
in two- or four-light systems. A pilot on the correct glide slope
will see two white lights and two red lights. See VASI.
Precision approach radar (PAR). A type of radar used
at an airport to guide an aircraft through the final stages of
landing, providing horizontal and vertical guidance. The
radar operator directs the pilot to change heading or adjust
the descent rate to keep the aircraft on a path that allows it
to touch down at the correct spot on the runway.
Precision runway monitor (PRM). System allows
simultaneous, independent Instrument Flight Rules (IFR)
approaches at airports with closely spaced parallel runways.
Preferred IFR routes. Routes established in the major
terminal and en route environments to increase system
efficiency and capacity. IFR clearances are issued based on
these routes, listed in the A/FD except when severe weather
avoidance procedures or other factors dictate otherwise.
Pressure altitude. Altitude above the standard 29.92" Hg
plane.
Prevailing visibility. The greatest horizontal visibility
equaled or exceeded throughout at least half the horizon
circle (which is not necessarily continuous).
Primary and supporting. A method of attitude instrument
flying using the instrument that provides the most direct
indication of attitude and performance.
Primary flight display (PFD). A display that provides
increased situational awareness to the pilot by replacing the
traditional six instruments used for instrument flight with
an easy-to-scan display that provides the horizon, airspeed,
altitude, vertical speed, trend, trim, rate of turn among other
key relevant indications.
PRM. See precision runway monitor.
Procedure turn. A maneuver prescribed when it is necessary
to reverse direction to establish an aircraft on the intermediate
approach segment or final approach course.