Installed a Trig TT31 with a Garmin GPS20A feed for ADSB and initially had problems with the airborne performance check getting the Trig to switch from Airborne to Ground on landing. Eventually installed an airspeed switch which did the trick, but only after setting the Trig system setup selection "Squat Switch Source" to "Low when airborne" instead of "not connected".
When I eventually took the aircraft to the avionics shop for the Biannual Transponder check, the only way we could check the transponder with the test box was to disconnect the GPS20A, and then to again select "not connected" in the Trig setup Squat Switch Source selection to force the unit into the airborne mode. I then got a pass on the Biannual Transponder check.
The TT31 manual while generally good did not mention the options available for the setup Squat Switch selections, at least where I could see. They are, at least for my unit:
"not connected"
"Low when airborne"
"Low when GND"
"Auto on GPS"
It is entirely possible that I could have avoided using an airspeed switch if I had tried the "Auto on GPS" selection before the airborne performance check. I am not sure if the TT22 has the same setup or options.
When I eventually took the aircraft to the avionics shop for the Biannual Transponder check, the only way we could check the transponder with the test box was to disconnect the GPS20A, and then to again select "not connected" in the Trig setup Squat Switch Source selection to force the unit into the airborne mode. I then got a pass on the Biannual Transponder check.
The TT31 manual while generally good did not mention the options available for the setup Squat Switch selections, at least where I could see. They are, at least for my unit:
"not connected"
"Low when airborne"
"Low when GND"
"Auto on GPS"
It is entirely possible that I could have avoided using an airspeed switch if I had tried the "Auto on GPS" selection before the airborne performance check. I am not sure if the TT22 has the same setup or options.