Link (via Schneier)
U.S. Patent 6844817, Aircraft anti-terrorism security system, by Wolfgang Gleine. Issued Jan 18, 2005.
Problem: Terrorists want to hijack a plane by trying to break down the cockpit door.
Solution: After hardening the cockpit door, airlines should add the next logical step: airplane trap door that springs open to entrap terrorists below deck.
Bonus: Great prank to pull on the co-pilot going on a bathroom break.
Improvement Suggestion: Add an alligator pit to the trap door ...