For all we know maybe the passenger had a panic attack, grabbed the controls and froze on them. I had that happen to me years ago. While very unlikely to be the cause of this accident a discussion on how to deal with such a passenger may serve a purpose for someone in the future.
Somewhere in the back of my mind I seem to remember being told of an accident to a perfectly serviceable aircraft in lovely weather, which initially appeared inexplicable. If I recall correctly, the pilot was flying his toddler of about 2 years and his father. The aircraft, I think, spun into the ground.Very careful examination by the AAIB concluded that the grandfather had reached back to the child and in doing so pushed the control column forward and the aircraft entered an unrecoverable spin. The conclusion was based on hand and fingerprints and their location within the aircraft.
.....crash happened to an aircraft that I had actually flown and to a pilot ......
Now months later still no word from The AAIB, still no definative reasons but the accident no longer shocks. It is becoming a distant and forgotten memory.
Pace, I can understand that as I too knew the pilot of an aircraft which crashed earlier in the year and although there is probably less of a mystery concerning the cause no report has yet been made. It may well be there were factors as yet unrevealed to us.
Whatever the eventual conclusion to any accident the only sure thing is that somewhere there is a least one family which is suffering the loss of a member. In this case it is even more sad as two young children have ben left without their parents and one of those is too young to be able to have any real memories of them.