Here, the "victory condition" for the bad guys would be to control the cockpit long enough to arrive at their destination. They will try to minimize this time period, right? A platoon of hijackers and their chemicals would have to accomplish a long list of tasks in order for their victory condition to obtain.
The on-board civilian response alone would have them outnumbered, but the attrition caused by the terrorist's whole chemical and bloody horror schtick may reduce the ratio of fit responders to perhaps two-to-one, perhaps. That will still be enough to thwart the bad guys' plans.
Unless they intend on using timing to force an early landing to somewhere specific.
Subthread stops here.