On Wednesday, March 21, 2018 at 7:15:00 PM UTC-7, Ramy wrote:
I am not aware of mode S and flarm deduplication so what you see is expected behavior. The problem is in the LX9000 side as I pointed out in another thread. They promised to have an option to turn off PCAS collision alarm from mode c/s which is what you need. You will still get timely alerts but not annoying alarm if they implement it correctly.
ADSB is a different case. Flarm suppose to ignore the ADSB signal when receiving flarm signal. I sure hope it is working as expected. If not I will find out soon that I am driving my buddies crazy when thermaling together.

Ramy

Mode S PCAS is _supposed_ to deduplicate in the PowerFLARM, a Mode S PCAS alert detects the target aircraft's ICAO address, if the PowerFLARM sees the same ICAO address via ADS-B Out or FLARM it should ignore the PCAS. As I've pointed out before, the main issue with spurious *PCAS* alerts is you can't stop Mode S transponders being interrogated by legacy Mode C (not Mode S capable) interrogators and then your transponder has to reply with an old style Mode C reply with no Mode S ICAO address. And then your PowerFLARM will have a lot harder job of trying to guess if it needs to deduplicate that PCAS traffic vs 1090ES or FLARM warnings. And sure there are lots of room here for things to still not happen properly, including between the PowerFLARM and display (e.g. timing windows between when different signals are received).

The classic example of a device that causes those Mode C interrogations is the Ryan TCAD interrogators still flying around in some GA aircraft, they were Mode C not Mode S capable and an aircraft equipped with one of those within several tens of miles of you may cause these issues with non-deduplicated targets and self-targets. TCAS I and II systems are Mode S interrogators so should not do this.

This discussion has already got to confusing levels. Are we talking FLARM actual warnings or LXNav handling of them. 1090ES traffic or PCAS etc. I've gotten lost. And really belongs in a discussion with the appropriate vendors, as we all see to be agreeing on.