My earlier posting hypothesizes that the initiating event was the failure of the flight control computer or perhaps that some event disconnected it from the flight control system. [ In the Air France 447 disaster, the flight control computer disconnected when the pitot tubes iced-up. In the Air Asia 8501 disaster, the pilot pulled its circuit breaker.] For those interested, a complete explanation of the Airbus Flight Control Laws can be found at the site:
My hypothesis is that the pilot found himself suddenly in the "Direct" Law control mode, and that means that he had to control the aircraft manually. Few pilots are skilled at controlling an A321 at altitude in Direct Law. Worse, flying the aircraft all the way through a descent from altitude, through an instrument approach, to a landing, all in Direct Mode, isn't really trained.
Some have asked me if I knew about the ADS-B trace, which indicated violent changes in altitude, and about the satellite detection of a "flash" which might indicate an explosion. The answer is that I have, and these preliminary indications do not in any way contradict my hypothesis about the flight control computer disconnect.
When the Flight Data recorder (FDR) and the Cockpit Voice Recorder (CVR) are analyzed, we may get some important answers. The analysis itself includes a careful time synchronization, so that all of the relevant data points are carefully matched in time. This might, for example, enable the ADS-B data to be matched exactly with the FDR data. A pessimistic outlook might be that the CVR and the FDR, being housed in the tail of the aircraft, stopped recording too early in the break-up process. We know that the tail separated inflight. So determining what happened will be an exercise in exquisite time synchronization. This process requires a great deal of skill. I might add that the Egyptian Government has the CVR and FDR and will do the investigation. Airbus will assist. The Russian Government will be present, but what they will actually do is not known. The Egyptian Government will also control the release of this information.
The wreckage itself will provide extremely important and useful information to the investigators. For example, explosions usually leave burn marks. Fracture surfaces show how the aircraft came apart. An explosion outside of the aircraft causes metal to fold inward, while explosions inside of the aircraft cause outward bending of metal. We will see how this unfolds.
If, as I suspect, the Flight Control Computers disconnected from the flight control system, that event should be recorded on the FDR. The CVR may have a recording of the pilot's surprised reaction.
Again - we will see.