I was talking about this very thing last night with a friend. I speculated that such an attack may already be in place, waiting only for our first strike at a Moslem country.
While everybody is focusing on American Airlines, the real threat may be Bob's Flying Service.
I don't know what you do about it. If they can hijack an airliner, Bob won't be much problem at all.
bob needs to carry a loaded .45 and be trained and prepared to use it. a cell phone to call cleanup (911) would be good too.