On Thursday, May 3, 2018 at 7:42:20 AM UTC-7, wrote:
On Wednesday, May 2, 2018 at 11:39:37 PM UTC-4, Darryl Ramm wrote:
^ BTW PowerFLARM (with the ADS-B option) also includes a PCAS capability

Darryl, can you explain that further, for those of us who are dazed and stupefied when confronted with the FAA's alphabet soup? AFAIK, PF does not transmit anything that the ATC system receives, so how can it give you collision warnings for non-FLARM aircraft, other than the warning about the presence of a transmitting transponder nearby?

That's all PowerFLARM does for transponder threats: PCAS. PowerFLARM does not transmit anything seen by ATC or non-FLARM/PowerFLARM equipped aircraft.

Almost all PowerFLARM in the USA have the "ADS-B" option which also includes PCAS capability. PCAS systems listens for transponders replying to other interrogators (SSR, TCAS, TCAD). It sees the altitude reported in those Mode C or S replies and guesses the distance from the received power. So accurate altitude, approximate distance and no directional information.

Also, you say a cheap used mode C transponder is a good addition to a glider. Can you explain further what that will get you? E.g.,
will ATC still see you after 2020?

Yes. There is nothing happening in 2020 that affects this, including the ADS-B Out carriage mandate becoming effective.

Will PowerFLARM devices sense your mode C transponder transmissions?

Yes. As long as your Transponder is being interrogated by SSR (aka ATC radar), TCAS or TCAD (lower-cost TCAS like systems). But only PowerFLARM with the ADS-B option, which almost all in the USA have, ...*don't* buy PowerFLARM "Pure" in the USA. There are settings in the PowerFLARM that can disable PCAS or adjust the filtering of PCAS targets.

Will the collision-avoidance equipment on airliners detect you, now and in the future?

Yes. That's one of the big reasons for getting a transponder, Mode C or Mode S. In fact TCAS requires a transponder in the threat aircraft, if your aircraft happens to have UAT Out and no transponder... TCAS II will let an airliner fly right into your glider with no collision RA (which is the main reasons that UAT Out in gliders was always a bad idea).

There is no plan to end of life Mode C in the USA, there was some talk from the FAA on long term reducing the number of approach radar systems (which would impact Mode S transponder without ADS-B Out equally). None of that seems to be even planned yet. There already issues with ADS-B Out equipage being behind schedule, and removing some approach radar systems has other issues, including possible national security ones.

One downside of Mode C transponders near other gliders is that the Mode C transponder replies unlike Mode S replies do not contain an ICAO number and its harder for the PowerFLARM to guess say that a PowerFLARM and Mode C equipped glider are the same target. But this is also going to happen at times when Mode S transponders get interrogated by a old Mode C interrogator, like most of the TCAD systems flying around... then the Mode S transponder has to emulate a Mode C transponder.

My message for a long time has been: If you fly near areas of dense airliners, fast jets and military traffic, just get a transponder, Mode S or used Mode C does not matter... get what you can afford.

Mode S, at least with a Trig transponder, has the additional benefit of being able to do ADS-B Out. Not all Mode S transponders can do ADS-B out or TABS. The Trig TT22 is currently *the* Mode S transponder to purchase for ADS-B Out in gliders in that USA.