On Wednesday, May 6, 2015 at 11:08:27 PM UTC-7, Mike Schumann wrote:

The question is, do you want to end up with an avionics package that doesn't see UAT ADS-B OUT equipped traffic? It's hard to predict how much of the GA or UAV fleet will go down that road, but it could be a pretty significant percentage if there is a significant price difference between UAT and 1090ES ADS-B OUT solutions.

That's not really the right question. The question is how do you trade off total cost versus the probability of potential collision scenarios.

If you can only afford a single device for most glider pilots the right choice is a PowerFlarm, which will get you anticollision for other PF-equipped gliders, plus PCAS for all transponder-equipped aircraft being painted by SSR or TCAS, plus 1090ES In for most (and in 2020 ALL) aircraft that fly in Class A.

Under some less common circumstances your best choice if you can afford only once device is to buy a transponder (preferably Mode S). This will make you visible to most high-performance aircraft equipped with TCAS AND to SSR AND to GA with PCAS. Modern Mode S transponders also have an upgrade path to 1090ES Out which will make you visible to most ADS-B equipped aircraft either directly or via ADS-R. Keep in mind that it is generally better for the higher performance aircraft to detect the lower performance aircraft rather than the other way around as they have more degrees of freedom.

If you can afford two devices you are best off installing a PowerFlarm AND a transponder. This will allow you to see and/or be seen by all transponder, PowerFlarm and 1090ES Out aircraft and will allow you to upgrade to 1090ES Out which will also make you visible to aircraft carrying UAT In/Out but aren't carrying a transponder or talking to ATC - not sure how many of these there will be given the regulations overlap between ADS-B and transponders.

If you want to install three devices you can consider UAT-In - this will additionally give you coverage of aircraft that are not carrying a transponder but are carrying UAT Out. It will also allow you better granularity in seeing UAT-Out aircraft and any UAVs that are flying outside MOAs or wander above the 400' FAA limit ASSUMING they are equipped with UAT instead of 1090ES - not clear that UAVs are going to be a big deal or that UAT would be preferred to 1090ES for them. Based on the statistics, this does not seem like a good return on investment in terms of risk reduction. I am personally skeptical that many GA aircraft will equip with UAT Out over 1090ES Out and am particularly skeptical that they will eschew transponder carriage so you wouldn't see them on PowerFlarm's PCAS.

The idea of picking UAT In before PowerFlarm and/or a Mode S transponder defies all the traffic, equipment and collision statistics. If you want it as a third device knock yourself out, but it is definitely well past the point of diminishing returns.

9B