We would probably be like stunned deers in the headlights. Also, it was believed that up to 5 terrorists were on board, it would require some quick thinking to get other passengers to attack with you. Forget MacGyver, Indiana Jones and other heros, it would be near impossible to take down 5 terrorists without being armed. You can only do so many karate moves in the aisles of a 757.
However, it seems on the 4th plane, they did come together but only after possibly realizing what was going on and that they were going to die anyway. In that case I would fight. A cornered rat fights to the death.
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"Fly me to the moon and let me earn alot of miles."