Contrary to what the Malaysians have said, the transponder was not "turned off" in the cockpit, nor did it climb to 44,700 feet (too heavy) or descend to 5000 feet (groundspeed would be too low).
Mode S was dropped from the radar (but when was it coasted?) around the time the aircraft was turning at Igari, then 37 seconds later, the secondary radar symbol disappeared. How can you just turn off Mode S from the cockpit? Even turning the selector to ALT RPTG OFF still transmits Mode S. It is more likely that the transponder had lost air data from the LEFT AIMS cabinet in the MEC.
Interestingly when the satcom did log on again at 18:25 the flight ID was missing. The flight ID is sent to the SDU only from the LEFT AIMS.
So, if the LEFT AIMS is damaged, that's a major problem, since it interacts with over 100 LRUs, switches and sensors! It's the left electronic brain.
The Audio Management Unit must be operational to make any radio call. The AMU uses the LEFT systems ARINC 629 bus.
The aircraft satcom had unique dual side mounted Ball Aerospace high gain antennas (HGA). If the LEFT AIMS is damaged, then there is no IRS data for the Left HGA mounted on the left side of the fuselage. However the right HGA would be operational since IRS data is from the Right AIMS. Amazingly at 1825, around the time when the right hga is first exposed to the satellite, as the aircraft rolls left at Nilam (but still heading northwest), for a diversion to Banda Aceh via Nilam-Sanob, the satcom logs on again! The Crew could have been incapacitated well before this time.
Then if the aircraft continues on over Banda Aceh it hits all the BTO arcs, meets the BFO requirements and ends at the Bayesian approach hotspot in the southern Indian Ocean. However, if it is still at FL350, then there is still fuel in the tanks at 0017:30. So, either the APU was on (meaning the aircraft is south of the hotspot beyond 40 nautical miles), or the left engine was still operating (Left GCU and backup converter inop) when the APU auto started and repowered the Satcom via the Left Mains AC bus.
If they want to find MH370 they should search the full 100 nautical mile radius from the Bayesian hotspot (approx 38S88E), not just to 40 nautical miles along the seventh arc.
If they want evidence, just ask them to release the withheld information: playback of secondary radar, Vietnamese ATC transcript of call with MH88, the FOs phone connection logs with Penang and Banda Aceh, playback of the multiple Indonesian Primary radars, Malaysian 10 sec primary radar, fuel report, etc
So what damaged the LEFT AIMS Cabinet? Most likely, the adjacent Crew oxygen bottle ruptured - it was topped up immediately prior to flight!