Blackcap,
Thanks for the info. And without in any way wishing to shoot the messanger, I'm horrified.
I don't understand the design philosophy in the first case. A transponder head that Turns Off the active squawk because you get interupted changing it? Thats almost incredible. I can't see any rationale for that. Make the standby code blank, make it flash, I'd even at a push accept the box reverting to conspicuity, but standby? <boggles>
So there is now an SOP whereby, during an emergency descent, the need to set 7700 is making the aircraft invisible to ATC and other aircrafts TCAS, and incidentally also disabling the aircrafts own TCAS. Thats insane, even if its only for a few seconds.
I don't suppose you could offer the manufacturer and model of the control head?
pb