On Saturday, April 19, 2014 1:31:15 AM UTC-7, Ramy wrote:
"I suspect that in practice, suppressing transponders at the exact same altitude will have no much affect on PCAS reliability, as relative altitude between aircrafts fluctuate all the time, especially with gliders, and I suspect the suppression algorithm can detect altitude fluctuation and does not suppress it. This is just my guess based on the fact that my PF seem to do good job with PCAS alert even when flying at the same altitude as someone else."

The relative altitude between gliders may be subject to large fluctuations. The relative altitude between powered aircraft is quite likely not to vary by more that the typical 100ft resolution of the altitude encoder interface.

I have first hand experience of being on a same altitude, opposite heading, less that 500ft lateral offset threat. ZAON PCAS alerted. I acquired the aircraft visually then checked PF portable. The target was never indicated or alerted.

ZAON used, perhaps inter alia, the signal strength to determine if a mode C signal is own ship. That is why there is provision in the calibration menus for adjusting each unit for own transponder signal strength. To the best of my knowledge FLARM units have no such provision for user calibration.

Andy