Like many pilots, I have long used portable GPS navigators with SiriusXM aviation weather to display NEXRAD, weather reports and forecasts, and TFRs in the cockpit. Having regularly updated (if not truly real-time) information about the weather has been a boon to safety and efficiency, making strategic decisions about weather-related diversions and other changes to the original plan for a flight much less cumbersome.
The introduction of aviation apps for the iPad and other tablets and the completion of the ADS-B ground infrastructure has more pilots using the free Flight Information Service (FIS-B) products that can be integrated into products such as ForeFlight, WingX, FlyQ, and Garmin Pilot–provided you have an ADS-B receiver, such as the Stratus, Garmin GDL 39, or Dual XGPS170, among others.
(SiriusXM has announced a new, stand-alone receiver for its subscription services. It works with the iPad and a dedicated app. Details here.)
SiriusXM and FIS-B: What’s different?
If you’re switching from the satellite-based weather and information services to FIS-B products, it’s important to understand several key differences between the information each provides, and the limitations of the FIS-B services, especially for typical general aviation pilots operating below the flight levels who want to check the weather more than 375 nm ahead.
Of course, it’s also important to understand that SiriusXM information is available even on the ground, assuming the antenna has a clear view of the sky. FIS-B services, based on line-of-sight transmissions from ground stations, typically are available only after you climb at least above pattern altitude; higher minimums often apply. You can view a map of and learn more about ADS-B coverage here.
First, the set of weather reports and forecasts available via FIS-B doesn’t include all of the products from SiriusXM (depending on the subscription plan you choose).
FIS-B includes the following text reports (see AIM 7-1-11):
- Aviation Routine Weather Report (METAR) and Special Aviation Report (SPECI)
- Pilot Weather Report (PIREP)
- Winds and Temperatures Aloft
- Terminal Aerodrome Forecast (TAF) and amendments
- Notice to Airmen (NOTAM) Distant and Flight Data Center
FIS-B includes the following products in both text and graphic forms:
- Airmen’s Meteorological Conditions (AIRMET)
- Significant Meteorological Conditions (SIGMET)
- Convective SIGMET
- Special Use Airspace (SUA)
- Temporary Flight Restriction (TFR) NOTAM
FIS-B also displays graphical regional and national NEXRAD composite reflectivity information.
AIM Table 7-1-1 FIS-B Over UAT Product Update and Transmission Intervals shows the intervals at which fresh information is transmitted via the ADS-B network.
Look-Ahead and Altitude Tiers
To avoid overloading the ADS-B transmitters, the amount of information sent to aircraft depends on the altitude of the receiver. The altitude tiers are described in AIM Table 7-1-2 Product Parameters for Low/Medium/High Altitude Tier Radios:
Figure A-2 in AC 00-63A defines the altitude tiers:
Most of us flying normally aspirated, piston aircraft fit into the medium altitude tier, which means that some information (e.g., METARs and TAFs) is available only when the reporting airport is within 375 nm of our present position.
The advisory circular notes that:
Pilots need to consider the performance of the aircraft as well as the update rate for a specific product. For example, a pilot of a light twin aircraft, flying at a medium altitude with a tailwind could easily have a ground speed in excess of 200 knots. Thus, traveling at over 3 NM per minute, a pilot may not have enough time to receive and decipher a pop-up TFR based on the 100 NM look-ahead and a 10-minute transmission interval.
Future FIS-B Products
AC 00-63A notes that FAA plans to add five new FIS-B products “in the next few years.” These products include:
- Lightning. Graphical representation of each lightning stroke in a past 5-minute period.
- Turbulence NOWcast. Two-kilometer resolution grid containing an eight-value turbulence intensity scale in each grid cell. The intensity scale depicts a weighted average turbulence for flight levels (FL) of 10,000 ft and above.
- Icing NOWcast. Two-kilometer resolution grids, where each grid represents one of the eight 3,000 ft ranges from FL 030 to FL 240. Within each grid, each grid cell contains the four-value icing indication and the presence or absence of Supercooled Large Drop (SLD) formation.
- Cloud Tops. Two-kilometer resolution grid indicating the altitude of the cloud top to an accuracy of 3,000 ft, ranging from FL 030 to FL 480.
- One-Minute Automated Weather Observing System (AWOS). More frequent updates of METAR-formatted information.
More Information and Key References
You can find detailed information about FIS-B in the following key references:
In June 2012, NTSB released a Safety Alert about the limitations of NEXRAD displays in the cockpit.
AOPA ASI offers a free online course, IFR Insights: Cockpit Weather, to help you learn more about datalink weather.