my moneys on an avionics bay fire.
sure theres multpile redundancies on the system but all the systems are in the same place.
I recon the fire took out the comms (not going to speculate on fire VS explosion VS terrorist just that something took out the avionics bay) first and they were trying to leg it to land. when the whole damn fly by electronics thing just went melty and with the glide ability of a cement glider it was just a matter of time.

