For that matter, arm the passengers, too. Even on international flights, at the end of the flight in, say, Old Blighty they Stew couold make an announcement: "All armed passengers remain seated please, and prepare your storage boxes" Then the armed folks could come to the front, clear their weapons in a clearing-barrel, and place them in locked boxes for the airline to store until their return trip.
Had the passsengers aboard the 9-11 planes been armed, there MIGHT
have been four planes crash just as they did; but it's a lead-pipe cinch
the World Trade Center would still be standing and the Pentagon would not have one section that is only ten years old.
However, needless to say, if the Twin Towers had not been hit, it would have been chalked up as a lesson on why you need to cooperate with the bad guys so nobody gets hurt.....