The best thing to do is to stay calm and try to build up a concenssus of what to do and when to do with others onboard…If there are say 5-6 terrorists then u’re looking at about 10-12 willing people to do the trick remembering that it only takes a few to pin em down cuz u have the element of surprise with u..Secondly the most important thing to do is to organize a counterattack in such a way as to give them little reactionary time to say do something radical like charge the cockpit in desperate attempt..Speed and Surprise are the key..Once the initial attack is made by 6-10 people the ripple effect of other less willing passengers will naturally follow..However u have to wait for the response from the actual security people present on the aircraft which are armed with Dum Dum Bullets etc etc..However the situation is a catch 22 the marshals onboard are probably communicating with one another and probably have a plan in place to counter the terrorists and deal with them..Unnec. heroics from a avg joe passenger might work adversly for them