[kcope]

Chances are nowdays if you have a terrorist on board your dead anyway. What difference does a hole in the plane make. At least the passengers and crew are belted in and have oxygen available.
If its any comfort to you fliers out there the ammo carried by sky marshalls and pilots is a special low velocity fragable variety thats not as likely to put a hole in the skin of a plane.
Most combat shooting situations are panic scenerios, even an expert is going to miss some of his shots so a person with out much training might only get one hit on target but that might be enough.