I was watching CNN late last night, and various people were discussing potential counter terrorism measures.
One that was sent in by email to them which I thought was interesting, was the idea that all commercial jets be retrofitted with a vault like door, sealing those in the cockpit and making it inpenetrable.
As well tv-like monitors within the cockpit, with hidden cameras and microphones within the passenger areas, give them the ability to see and hear all of the passengers and to be able to detect trouble.
Once the trouble has been determined (assuming it is a hi-jacking in progress), a button is pushed in the cockpit and a harmless gas is released in all of the passenger sections, and everyone goes to sleep for the duration of the flight.
1 or 2 security people (also riding in the cockpit,) then go out into the passenger areas with oxygen masks on, disarm and hand-cuff the sleeping high jackers, and when the plane lands hi-jackers are arrested, passengers wake up, and board a different plane to continue to their destinations.