My earlier article summarised the basic known facts.  Much of this new article is taken from the Royal Aeronautical Society article here http://aerosociety.com/News/Insight-Blog/2007/What-happened-to-flight-MH370 and here is a summary of the main theories of what might have happened:

Theories

1) Depressurisation or toxic fumes – this would explain the change in heading and altitude (to move towards another airfield to land) but not the loss of communications, in either case the pilots could have communicated for a while, and would not have turned the transponder or ACARS off.

2) Hijacking – post 9/11 this is much more difficult than it once was, and the aircraft wasn’t flown to a new destination, or crashed into a building as usual with hijacking, and no sign of concern was shown by the pilots.  If hijacked, why was the ACARS system turned off and why has no group claimed responsibility?

3) Deliberate action by the pilots – no reason for this has ever been identified, if it was a pilot suicide (such as the Germanwings and Egyptair flights) then why did the aircraft carry on flying for another 7 hours?

4) Fire on board – as with the 1998 Swissair MD11 flight https://en.wikipedia.org/wiki/Swissair_Flight_111 a flight deck fire could disable many systems.  The pilots’ initial response would be to turn off electrical systems while they diagnose the problem, which could lead to the radio and ACARS etc being switched off and the lack of communications. They would also turn towards the nearest airport, which could explain the westward turn towards Phuket and Langkawi.  However it would then be strange for the aircraft to carry on flying for another 7 hours if catastrophic damage had been experienced that prevented communications but allowed the aircraft to carry on flying.

5) A combination of two – a fire on board followed by a depressurisation or by  incapacitation of the pilots after they sorted out the source of the fire could lead to the events as known.  This would be unusual but it is equally unusual for a B777 to disappear in such strange circumstances.

Whatever the cause, unless the FDR and CVR or indeed the main wreckage is found, this will remain a real mystery.

Martin Fiddler