While ADS-B receivers have exploded in popularity over the past three years, some pilots assume these portable devices are only for piston airplanes. We’ve heard from more than one jet pilot something to the effect of, “ADS-B receivers sound great but I’ve heard they don’t work up high.” Some jet pilots who are using them might wonder if maybe they’re doing something wrong.
Why all the confusion? The answer comes from a rather obscure source: Advisory Circular 00-63A. This document, which discusses cockpit displays of weather information, has an appendix that spells out specifics about the ADS-B system and FIS-B (the technical term for ADS-B weather). In particular, one sentence describes “the upper limit of FIS-B service” as being FL240, or 24,000 ft. That would suggest that a jet cruising along at FL370 might be well out of range of a ground-based station.
But read the footnote and you’ll find a more complete answer:
While the required ceiling for FIS-B is FL 240, it is expected that users can access the FIS-B service above that altitude. In the present design, approximately 90 percent of the implemented Service Volumes have FIS-B coverage at FL 400.
If anything, that 90% number may be conservative. In our 3+ years of flying with the Appareo Stratus, Garmin GDL 39 and Dual XGPS170, we’ve logged hundreds of hours between FL240 and FL410. Weather comes in consistently – it’s not unusual to be receiving 10 ADS-B ground stations in the high 30s. There are also dozens of airline, military and business aviation organizations using ADS-B receivers. If it works in an Airbus it will work in a Citation or a Learjet.
This makes sense, since VORs are set up in much the same way (with low and hi stations). In general, the higher you go, the better the reception gets. Both ADS-B and VORs are line of sight transmissions, so the “cones of coverage” get larger as you climb. If you are concerned about coverage up high, consider mounting your ADS-B receiver on a side window, since the dash can block stations over the nose. If needed, external ADS-B antennas are another good option.
So can you count on ADS-B weather in a jet? Absolutely. Turn it on and fly.