TCAS/ATC Transponder Control Panel
Transponder Code Window
The Transponder Code Window indicates the code selected with the code selector.
DESCRIPTION - Two ATC transponders are controlled by a single control panel. In flight, the selected transponder replies to beacon code aircraft ID (Mode A), barometric altitude (Mode C), and aircraft ID flight data (Mode S) interrogations when the transponder mode selector is in XPNDR, TA ONLY, or TA/RA. On the ground, transponder replies are inhibited for general (all call) Mode A, C, and S interrogations. However, the transponder will reply to selective Mode S interrogations on the ground that are specifically directed to the aircraft, based on each aircraft’s unique Mode S address. This function can be used by ATC for ground surveillance during taxi when the transponder is active (mode selector not in STBY). All transponder modes are inhibited when the mode selector is in STBY.