One way to prevent takeover of an aircraft is to prevent access to the cockpit while in flight. As an aerospace engineer, I believe it would be relatively easy to change the design so that access and egress can be accomplished only on the ground.
It requires nothing more than a minor modification to airliners to wall off the cockpit and allow access through the nose wheel well or by using some other external door for access from outside.
The airline passenger is perhaps the one with the loudest voice in this matter. Would we prefer to fly on an aircraft with a cockpit inaccessible from the cabin? Maybe we should demand it.
Most of the reasons the cockpit is designed to be accessible in flight are not worth risking what happened on Sept. 11. When air travel was new, the emphasis was on making the flight environment as psychologically attractive as possible -- flight attendants, food and drink, entertainment, comfortable seats and surroundings. The cockpit was accessible then and it has remained so to this day.
A stronger door with a better lock is not the answer if anyone in the cabin has a key, because it could be obtained through threat of force. Likewise, a door that can be opened only from the cockpit is not a solution, since the pilots might be persuaded to open the door to save someone's life under threat and then be overpowered. A structural wall would prevent access regardless of the dire circumstances on board.
This change in cockpit design will not necessarily prevent forceful change of flight plan by threats from the cabin, but it will assure that ultimate control of the flight path remains with the original crew in the cockpit.
PAHILIP A. REYNOLDS