The point here is that crew and PAX are no longer going to comply with a hijacker's requests.



Ask the PAX that suffered severe burns while subduing the underpants bomber.

Poisonous gas? You should know that Part 121 aircraft have quick-donning full face masks with their own source of oxygen in the cockpit. What was it, the movie Airport '77 that had the the knock-out gas?

Any firearm or explosive capable of breaching a Kevlar door would more than likely cause enough damage to the point of making the aircraft incapable of being in controlled flight. But since you've come up with scenarios like a Hollywood script writer, here's an example of what the likely outcome would be like.