potential delay when using in-cockpit NEXRAD capabilities,
as the movement and/or intensification of weather could
adversely affect safety of flight.
• Understand that the common perception of a “5-minute
latency” with radar data is not always correct.
• Get your preflight weather briefing! Having in-cockpit
weather capabilities does not circumvent the need for
a complete weather briefing before takeoff.
• Use all appropriate sources of weather information to
make in-flight decisions.
• Let your fellow pilots know about the limitations of
in-cockpit NEXRAD.
NEXRAD Abnormalities
Although NEXRAD is a compilation of stations across
the country, there can be abnormalities associated with the
system. Some of the abnormalities are listed below.
• Ground clutter
• Strobes and spurious radar data
• Sun strobes, when the radar antenna points directly at
the sun
• Interference from buildings or mountains that may
cause shadows
• Military aircraft that deploy metallic dust and may
reflect the radar signature
NEXRAD Limitations
In addition to the abnormalities listed, the NEXRAD system
does have some specific limitations.
Base Reflectivity
The NEXRAD base reflectivity does not provide adequate
information from which to determine cloud layers or type
of precipitation with respect to hail versus rain. Therefore, a
pilot may mistake rain for hail.
In addition, the base reflectivity is sampled at the minimum
antenna elevation angle. With this minimum angle, an
individual site cannot depict high altitude storms directly
over the station. This leaves an area of null coverage if an
adjacent site does not also cover the affected area.
Resolution Display
The resolution of the displayed data poses additional concerns
when the range is decreased. The minimum resolution for
NEXRAD returns is 1.24 miles. This means that when the
display range is zoomed in to approximately ten miles, the
individual square return boxes are more prevalent. Each
square indicates the strongest display return within that 1.24
mile square area.
AIRMET/SIGMET Display
AIRMET/SIGMET information is available for the displayed
viewing range on the MFD. Some displays are capable of
displaying weather information for a 2,000 mile range.
AIRMETS/SIGMETS are displayed by dashed lines on the
map. [Figure 13-19]
The legend box denotes the various colors used to depict the
AIRMETs, such as icing, turbulence, IFR weather, mountain
obscuration, and surface winds. [Figure 13-20] The great
advantage of the graphically displayed AIRMET/SIGMET
boundary box is the pilot can see the extent of the area that
the advisory covers. The pilot does not need to manually plot
the points to determine the full extent of the coverage area.
Graphical METARs
METARs can be displayed on the MFD. Each reporting
station that has a METAR/TAF available is depicted by a flag
from the center of the airport symbol. Each flag is color coded
to depict the type of weather that is currently reported at that
station. A legend is available to assist users in determining
what each flag color represents. [Figure 13-21]
The graphical METAR display shows all available reporting
stations within the set viewing range. By setting the range
knob up to a 2,000 mile range, pilots can pan around the
display map to check the current conditions of various
airports along the route of flight.
By understanding what each colored flag indicates, a pilot can
quickly determine where weather patterns display marginal
weather, IFR, or areas of VFR. These flags make it easy to
determine weather at a specific airport should the need arise
to divert from the intended airport of landing.
Data Link Weather
Pilots now have the capability of receiving continuously
updated weather across the entire country at any altitude.
No longer are pilots restricted by radio range or geographic
isolations, such as mountains or valleys.
In addition, pilots no longer have to request specific
information from weather briefing personnel directly. When
the weather becomes questionable, radio congestion often
increases, delaying the timely exchange of valuable inflight
weather updates for a pilot’s specific route of flight. Flight
Service Station (FSS) personnel can communicate with only
one pilot at a time, which leaves other pilots waiting and
flying in uncertain weather conditions. Data link weather
Figure 13-19. The AIRMET information box instructs the pilot to press the ENTER button soft key (ENT) to gain additional information
on the selected area of weather. Once the ENTER soft key (ENT) is depressed, the specific textual information is displayed on the right
side of the screen.
Figure 13-20. SIGMET/AIRMET legend display.
Figure 13-21. Graphical METAR legend display.
provides the pilot with a powerful resource for enhanced
situational awareness at any time. Due to continuous data link
broadcasts, pilots can obtain a weather briefing by looking at
a display screen. Pilots have a choice between FAA-certified
devices or portable receivers as a source of weather data.
Data Link Weather Products
Flight Information Service- Broadcast (FIS-B)
Flight Information Service–Broadcast (FIS-B) is a ground
broadcast service provided through the Automatic Dependent
Surveillance–Broadcast (ADS-B) Services network over
the 978 MHz UAT data link. The FAA FIS-B system
provides pilots and flight crews of properly-equipped aircraft
with a flightdeck display of certain aviation weather and
aeronautical information which are listed below.
• Aviation Routine Weather Reports (METARs)
• Special Aviation Reports (SPECIs)
• Terminal Area Forecasts (TAFs) and their amendments
• NEXRAD (regional and CONUS) precipitation maps
• Notice to Airmen (NOTAM) Distant and Flight Data
Center
• Airmen’s Meteorological Conditions (AIRMET)
• Significant Meteorological Conditions (SIGMET) and
Convective SIGMET
• Status of Special Use Airspace (SUA)
• Temporary Flight Restrictions (TFRs)
• Winds and Temperatures Aloft.
• Pilot Reports (PIREPS)
• TIS-B service status
The weather products provided by FIS-B are for information
only. Therefore, these products do not meet the safety and
regulatory requirements of official weather products. The
weather products displayed on FIS-B should not be used
as primary weather products (i.e., aviation weather to meet
operational and safety requirements). Each aircraft system is
different and some of the data that is rendered can be up to
20 or 30 minutes old and not current. Pilots should consult
the individual equipment manuals for specific delay times.
Pilot Responsibility
It is important for pilots to understand the realization that the
derived safety benefits of data link depends heavily upon the
pilot’s understanding of the specific system’s capabilities and
limitations which are listed below.
• Product latency—be aware of the time stamp or “valid
until” time on the particular data link information
displayed in the flightdeck. For example, since initial
processing and transmission of NEXRAD data can
take several minutes, pilots must assume that data
link weather information will always be a minimum
of seven to eight minutes older than shown on the time
stamp and only use data link weather radar images for
broad strategic avoidance of adverse weather.
• Product update cycles—be aware of when and how
often a product is updated as well as the Data Link
Service Providers (DLSP) update rate for particular
products.
• Indication of system failure—be aware of partial or
total system failure indications.
• Coverage areas/service volume—coverage limitations
are associated with the type of data link network
being used. For example, ground-based systems that
require a line-of-sight may have relatively limited
coverage below 5,000 feet AGL. Satellite-based data
link weather systems can have limitations stemming
from whether the network is in geosynchronous orbit
or low earth orbit. Also, NWS NEXRAD coverage
has gaps, especially in the western states.
• Content/format—since service providers often refine
or enhance data link products for flightdeck display,
pilots must be familiar with the content, format, and
meaning of symbols and displays (i.e., the legend) in
the specific system.
• Data integrity/limitations to use—reliability of
information depicted. Be aware of any applicable
disclaimer provided by the service provider.
• Use of equipment/avionics display—pilots remain
responsible for the proper use of an electronic flight
bag (EFB) or installed avionics. Pilots should be
cognizant that, per the FAA Practical Test Standards,
they may be evaluated on the use and interpretation
of an EFB or installed avionics on the aircraft.
• Overload of Information—most DLSPs offer
numerous 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 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.
Chapter Summary
While no weather forecast is guaranteed to be 100 percent
accurate, pilots have access to a myriad of weather information
on which to base flight decisions. Weather products available
for preflight planning to en route information received over
the radio or via data link provide the pilot with the most
accurate and up-to-date information available. Each report
provides a piece of the weather puzzle. Pilots must use several
reports to get an overall picture and gain an understanding
of the weather that affects the safe completion of a flight.