Quote Originally Posted by RMAC757 View Post
To add ........dropping down to wave top level most likely wouldn't leave you with 8 hours of extra gas.
Ok...my thoughts are that the reason they went to a high altitude was to eliminate oxygen and kill or knock out the passengers...then went low to refill the plane with oxygen so the pilots (or whoever was flying the plane at that point) wouldn't have to use the masks.

I suspect someone wanted the plane for use as either a weapon or for terrorism training.