Malaysia MH-370 has just lost all comms and radar contact with ATC over the Gulf of Thailand.

Radar track shows where its intended and actual flight paths are. Last known recorded data for the aircraft, its altitude, heading, and position, it was at 35000 feet and made a rapid descent followed by a paradigm shift in heading. This means the following three situations:

1. A component or engine on the aircraft caught on fire in some form or fashion. Emergency dictates that you trade altitude for airspeed, since the force of the wind will hopefully extinguish the fire. Also, you bank the aircraft in such a way that the fire avoids spreading to the critical areas of the air frame, and more importantly, away from the passengers, crew, and cargo.

2. The aircraft lost pressure. Granted there is supplemental o2 for situations like this, however if you don't get the mask on quick your useful consciousness goes down quick fast and in a hurry. Pilots get asphyxiated, and that s all she wrote.

3. Similar to what happened to the Air France flight 337 that crashed over the coast of Brazil quite some time ago, the primary airspeed instruments had some sort of malfunction or problem. There is always a redundant system on the aircraft, but, if both fail, the aircraft could trick itself into thinking its loosing airspeed and approaching the stall. There is a thing called a stick shaker to avoid that from happening. However, if prompt action is not taken, the aircraft will loose lift over the wing and control surfaces and simply fall out of the sky. Worse, if there is no rudder added into the corrective action (pilots call this lack of coordination), the aircraft could go into a spin. 

Any of these situations do not bode well. I am sure the pilots were well trained, but the only thing that I am going to go with is #1 or #2. I doubt the bulkheads are that bad that it would suffer a catastrophic structural failure to the point the aircraft falls apart, but I have been wrong before. I am leaning towards #1.