Setting the ground-speed recognition function that activates airborn/ground modes the GTX 330.
This is not documented in the Garmin install manuals or the pilot operating manual anywhere, but it works. Strangest thing I’ve ever encountered in a Garmin unit. But at least it works.
Nowhere in the setup pages is there a configuration for auto standby or auto detect.
Now that we are required to have the transponder in ALT mode on the ground, I did the same thing with the ALT button and now it stays in ALT all the time.