Originally Posted by TheSquealer

This was discussed and ruled out in the very beginning. They were still plotting GPS way points in the nav system, following standard flight corridors that took them way out of the way, well after the fact and after all the erratic maneuvers. They had no intention to land at the nearest airport.

A startlingly simple explanation is that they planned to make it look as if there was a catastrophic event on board through the execution of a series of well thought out and well planned events... and then stole the plane.