Which to buy? 978 or 1090 MHz ADS-B OUT

Which to buy? 1090 or 978?   As the deadline for equipping aircraft with ADS-B Out approaches, aircraft operators will naturally be learning more about the technology as they get ready to make a decision on which system is right for their aircraft.  Perhaps the first decision is whether to look at ADS-B OUT transponder that operates at 1090 MHz or at 978 MHz as a means to narrow down the candidate products to consider.

Why does it matter whether an aircraft’s ADS-B OUT system transmits on 1090 MHz or 978 MHz?  It does – because while some 978 MHz ADS-B OUT systems may be cheaper to buy or install than their 1090 MHz competitors, the choice of 978 MHz limits where an aircraft can legally operate.  Specifically, a  978 MHz ADS-B OUT systems can only be used in the United States, and only below 18,000’ MSL. So if you fly outside the United States or very high, you’ll need a 1090 MHz system.  But for a lot of general aviation aircraft, particularly small piston aircraft, 978 MHz systems ought to be fine unless a trip to the Bahamas, Mexico, or Canada is a possibility.

Just as a review, if an owner/operator is still thinking about whether then need an ADS-B Out system at all, as of January 1st, 2010, the FAA1says you’ll need a validated ADS-B Out system to fly in:

  • Class A, B, and C airspace
  • Class E airspace above 10,000 feet (unless with 2,500’ of the surface, such as the mountainous terrain in the Rockies)
  • Class E airspace at and above 3,000’ over the U.S. coastline out to 12 NM
  • Some other airports listed in Appendix D of 14 CFR 91
FAA depiction of airspace requiring use of an ADS-B OUT transmitter after December 30th, 2019.

So in practical terms, as a Florida pilot where we have several Class B and C airports and often fly near the coastline, ADS-B OUT is necessary.  But as I don’t plan to fly to the Bahamas and my aircraft can’t get to 18,000’ MSL, I’ll be looking hard a few 978 MHz systems that have caught my eye.

One contender is the skyBeacon by uAvionix2.  That system is attractive because of its easy installation, and it includes a certified WAAS GPS, altitude encoder, and the UAT transmitter for ADS-B OUT.  The skyBeacon also replaces the aircraft’s existing position and anti-collision lights on the left wing.  When paired with the yet-to-be-released skyLight, which will replace the right side position and anti-collision lights as well as add an ADS-B IN receiver, it would seem that the total electrical load required to operate lighting at night will be reduced.  That seems like it would be a bonus should the alternator fail.


  1. https://www.faa.gov/nextgen/equipadsb/research/airspace/
  2. https://uavionix.com/products/skybeacon/

Photo: https://www.faa.gov/nextgen/equipadsb/research/airspace/

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