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Two things to note:

Aireon doesn’t work with UAT. This is yet another reason to avoid UAT. Aireon only picks up 1090 MHz, thus 1090ES ADS-B as is used worldwide.

A top mounted antenna is not “necessary” for Aireon. It will pick up signals from bottom transponder antennas, just not as easily as top ones. This is especially true for smaller airplanes. I would like the FAA to study the efficacy of bottom only ADS-B transponder in being heard by Aireon satellites. The data is there beause lots of bottom mounted airplanes are flying and the FAA has ground data to cmpare with Aireon data. Let’s not burden the owners if there isn’t a true need.

It should be noted that top mounted antennas do have a null zone directly overhead. This is the nature of a simple whip antenna. Therefore, a top mounted antenna also has dead zones and is not a 100% reliable antenna for a satellite passing directly overhead.

The Canadians are trying to force use of top mounted diversity transponders to use Aireon. This is a mistake, IMO. Basically, Aireon could have made a better satellite antenna and receiver to work with bottom mounted antennas, but they didn’t and now want to burden the owners will solving their problem.

Currently the FAA requires the use of an ELT but it can be an old 121.5 MHz only unit that nobody monitors, which is kind of stupid. Instead of forcing everyone to upgrade to 406 MHz ELTs, I think the FAA should delete the requirement for ELTs altogether if you have 1090ES ADS-B and carry a PLB with you in the plane. 1090ES ADS-B is now monitored by the FAA ground station network, by Aireon satellite network, and by 100,000 plus private ADS-B receivers all over the world. A lost airplane will be tracked to very near where it is, and that works WAY more reliably than any ELT ever could. If you survive the crash and have a PLB, then you can trigger it. If you don’t survive, then the ADS-B track will end the search far more quickly than a failed 121.5 MHz ELT ever would.

Mike C.

1 reply

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Precisely, Mike. And rather than – at some mythical point in future time – requiring a diversity transponder, I wonder if someone could come up with a way of splitting the signal OR an add on box to do the same IF it is determined that sat based ADS-B is the way to go. I predict the FAA will suddenly decide the cost of maintaining all the ground stations is too high and require diversity or some equivalent. IF they negate the need for an ELT … that wouldn’t be too onerous.

2 replies

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I think they already have come up with a box, Larry. Not exactly what you had in mind, but the UAvionix tail beacon has already been redesigned with twin antennae - one pointing up and one down for just that purpose. This move means the camel has its nose under the FAA’s tent. Hang onto your wallets boys and girls, diversity is coming.

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PS: Ditching the ELT requirement for adopting diversity is a good idea except for those of us who already made the “upgrade” to a 406 ELT. My 121.5 unit died a couple years ago so I already had to bite that bullet.