Many aircraft manufacturers now include data link weather services with new electronic flight display (EFD) systems. EFDs give a pilot access to many of the data link weather services available.
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| Figure 1. Information page |
- Graphical NEXRAD data (NEXRAD)
- Graphical METAR data (METAR)
- Textual METAR data
- Textual terminal aerodrome forecasts (TAF)
- City forecast data
- Graphical wind data (WIND)
- Graphical echo tops (ECHO T,,,OPS)
- Graphical cloud tops (CLD TOPS)
- Graphical lightning strikes (LTNG)
- Graphical storm cell movement (CELL MOV)
- NEXRAD radar coverage (information displayed with the NEXRAD data)
- SIGMETs/AIRMETs (SIG/AIR)
- Surface analysis to include city forecasts (SFC)
- County warnings (COUNTY)
- Freezing levels (FRZ LVL)
- Hurricane track (CYCLONE)
- Temporary flight restrictions (TFR)
Pilots must be familiar with any EFD or MFD used and the data link weather products available on the display.
Weather Products Age and Expiration
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| Figure 2. List of weather products and the expiration times of each |
The Next Generation Weather Radar System (NEXRAD)
The NEXRAD system is comprised of a series of 159 Weather Surveillance Radar–1988 Doppler (WSR-88D) sites situated throughout the United States, as well as selected overseas sites. The NEXRAD system is a joint venture between the United States Department of Commerce (DOC), the United States DOD, as well as the United States Department of Transportation (DOT). The individual agencies that have control over the system are the NWS, Air Force Weather Agency (AFWA) and the FAA. [Figure 3]
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| Figure 3. NEXRAD radar display |
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| Figure 4. NEXRAD radar display (500 mile range). The individual color gradients can be easily discerned and interpreted via the legend in the upper right corner of the screen. Additional information can be gained by pressing the LEGEND soft key, which displays the legend page |
What Can Pilots Do?
Remember that the in-cockpit NEXRAD display depicts where the weather WAS, not where it IS. The age indicator does not show the age of the actual weather conditions, but rather the age of the mosaic image. The actual weather conditions could be up to 15 to 20 minutes OLDER than the age indicated on the display. You should consider this 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 5]
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| Figure 5. 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 |
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| Figure 6. SIGMET/AIRMET legend display |
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 7]
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| Figure 7. Graphical METAR legend display |
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 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 notmeet 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.