Right now I'm imagining ascenario where the hijackers insist that they only wish to land the plane at an unplanned destination. They have passengers under knife and gun, etc, but insist that no one will die if everyone cooperates. Being that the people are offered this little bit of light at the end of the tunnel, and if the terrorists play their cards right by keeping everyone alive, then I can see everyone giving no resistance. They'd stay sane and peaceful until they saw the next target building looming in the distance, and the uncomfortable intuition that the plane just now banked 'just so'.. At this point, it is probably too late for the agape of sacrificing one planeload to overcome the hijacker pilots, and, there will be loss of life on the ground.
I'd say it's time for new tacit rules.
1. Obviously, everyone in possession of a cell phone should be using the hell out of it, as possible, if only to get voice prints of highjackers and provide some augmentation or replacement for the blackbox, plus to give some idea of available heroism.
2. If the pilot is killed or replaced by terrorist pilots, the passengers have a high certainty that they need to do the right thing.
3. If the passengers are herded to the back of the plane, there's a high chance that they need to do the right thing.
4. Terrorists are possessed of an inner single-minded vision. There are many accounts of Americans who gave their lives to save a drowning, snowbound, inferno, etc, victim. There's a place in the lizard brain that can tap into a righteous rage that can save lives, and Americans don't have to be too civilized to use it, now that we've been served formal notice what the new rules are.
5. God help the terrorist who screws up and actually f'n Tells the passengers they're going to die. I hope he gets a big, wet, loving, ocular noogie in his last moments.