Re:You say: "Defense"... (Score 2, Informative)

Trying to make a way for a plane to not be able to go somewhere is a really convoluted way to go about this. If someone has taken over a plane, you don't want them to have control, period. As far as planes go, implement a system whereby either the pilot, or a satellite link may force the plane into an autopilot mode that may not be overridden. The plane will then fly to some predestined area, or be commanded to land somewhere else by someone sitting in a control tower if need be. Plane gets there, and asks where to land. If no answer is received it lands on a predetermined runway. Have a friendly, neighborhood SWAT team waiting at the airfield. You could even set up the plane to be controlled by an external pilot.

The systems already exist. The military already uses them. Autopilot systems are very capable of landing planes these days when needed. It's just a matter putting all the crap together to make an even bigger pile of crap so to speak.

Of course, this being slashdot, I'm an idiot and have no clue what I'm talking about. Feel free to post goatse links and pron stories in response.