In an attempt to get back to the thread (!), it looked to me like the entire incident started much earlier than is shown on most of the video news clips (which stick - not surprisingly - to the crash itself). On Sky they have shown a more complete clip which show the lead up to the incident and it looks to me like there was a failure at the start of the clip which could have been the root cause of the whole thing.
Best wait for the report - nobody ever knows - and guessing won't get us anywhere.
Sympathies to all....
JM