How about a dead man's switch. Press it every 10 minutes or the engines will stop an alarm will sound. And maybe even the cockpit door will become unlockable for flight attendants who have the correct code.

Last edited by Legend; 05/24/16 01:47 AM.
There is a theory which states that if ever anyone discovers exactly what the universe is for it will instantly disappear and be replaced by something even more inexplicable.
There is another theory which states that this has already happened.