Using GPS groundspeed to determine airborne status with these Trig installs is a frogging mess. I like Trig products but this is a cluster**** that should have been documented long ago. It’s not just wave flying, a strong headwind can have the ADS-B Out transmitting it is on the ground.

The “correct” thing to do...

If a 2020 compliant install with a TN72 (in an experimental glider) use the Pereguine STC kit for the TN70. Which is really just a pitot pressure “squat” switch and some t-adapters and pneumatic house pieces. The TT22 documentatin describes it connected between pin 19/ground. Test this with the transponder set to “ON”. As you (cough, carefully) apply pitot pressure you should see the transponder display switch from GND to ATL as the ASI passes about 27 knots. The pressure switch is easy to install, make sure it is connected with correct orientation (marked on the switch) between the pitot and static lines, easiest place is often just behind the ASI.

Any TT22/TN70 installs should be following the STC and using the pitot squat switch anyhow.

2020 Compliant installs are required by 14 CFR 91.227 to automatically switch between air and ground modes, it’s not clearly written there but it is an implied requirement.

If you are doing a TABS/SIL=1 install you are not required to have that automatic air/ground determination and can just set the squat switch to none or not connected (I can’t remember the exact value name) in the TT21/22 setup. That will transmit airborne messages at all times including when in the ground... as specifically allowed by TSO-C199.

If you are doing a SIL=0 install (to what save a few hundred dollars on a TN72)... ah your an idiot, and I am being polite.

I have explained to all the glider market Trig dealers in the past the importance of them selling a TN70 STC kit squat switch with any TN72 intended for every SIL=3/2020 compliant install. And I have pointed out to them how they order the kit through Edmo. If your dealer is not doing this, not asking or explaining this to you when you buy a TN72 then find a better dealer..

If folks want to use/source a different pressure switch that’s entirely possible, but I cannot reconnect any specific options there.