So what's the difference between A-A TACAN and normal?
Actually, from the Viper manual:
A/A T/R. TACAN operates in Air-to-Air transceiver mode and provides bearing, range, deviation, and station
identification with a TACAN-equipped aircraft.
T/R. The TACAN acts in a transceiver mode (send and receive) and provides bearing, range, deviation and
station identification. This will be your most common selection.
probably a bug or WiP