Here's an alternative:
Sleeping/ knockout Gas. Easy to fit and control, all flight decks have oxygen systems, no need to worry about training or legislation, no need to liase with countries you overfly with bans on weaponry so that you can divert safely. OK you may lose the odd grannie if you have to use it, but it's a damn sight safer than some wannabe rambo trying to fly a plane, turn 180 degrees in his seat and shoot one of the Bin's boys through the forehead. Tie this with reinforced doors, and the fact that it's a bit harder to get a gas mask onto an aircraft than a knife it seems the best option
