Quote:4. Is there a way to use it to indicate a problem on board the aircraft?
There are codes for different emergencies. For a hijacking, it's 7500. For communications failure, 7600. Emergencies are 7700.
5. How and why do you turn off a transponder?
There is a switch that you would move from "ON" or "SBY" (standby) or "ALT" (altitude). You could also pull the circuit breaker for the transponder in the cockpit.
see all these little stories, they are coming to an end soon, this goes to show all the experts have ran out of guesses, the closer you look the less you see ....