A really simple, no nonsense theory:

1. Fire aboard

2. Pilots immediately turn towards nearest useable airport

3. Pilots immediately switches off main circuits of (almost) everything (including transponders). (Supposedly standard procedure if the fire is belived to be caused by a short circuit).

4. Pilot incapicated and/or communication equipment destroyed in fire

5. Nobody really knows -- except that any concious pilot will do his outmost to save everyone.

6. RIP

http://www.wired.com/autopia/2014/03/mh370-electrical-fire/