Dhaka, Oct. 2 -- When flydubai flight FZ1073 suddenly lost more than half its cruising altitude over Saudi Arabia on Sept 30, there was little doubt that something extraordinary had happened aboard the aircraft.

Flight-tracking data recorded violent altitude changes. The aircraft transmitted first a general emergency code and then one signalling unlawful interference. Flydubai has confirmed an altercation on the flight deck, while Saudi Arabia says a preliminary investigation found that the co-pilot assaulted the captain.

What remains less clear is why it happened, precisely what occurred inside the cockpit and how much of the dramatic account that followed can yet be independently established.

Israeli officials say the co-pilot attack...