I think some kind of electrical fire. That would explain why systems were shut down. It would also explain the last recorded turn as the pilot tried to get to the nearest airport that could handle that size plane. Smoke/fire probably got serious enough to realize they couldn't make the airport and had to ditch the plane in the ocean, much like the plane in the Hudson River. He may have put the plane down somewhat successfully, but with enough damage that the plane soon swamped and went down virtually intact without a debris field.
...or again, Aliens.
If only Jack was still in business at the CTU, we'd get to the bottom of this mess in a hurry!
And if that's not enough, a disapproving stare from Chloe will get the info flowing.
Love that show! Just watched that top pic of jack episode the other day. Hopefully were caught up for season 8 release....
Im with the guy who said iran... But at the same time, the pilot has a point because I know we always have F-15s in the air in the PNW.