If the Australians are on to something, my guess is that the crew may have been incapacitated shortly after turning back but didn't radio an emergency for whatever reason. Then the aircraft was on autopilot until it ran out of fuel.
Some thoughts:
- I originally speculated that this may have been caused by a fire on board the aircraft. If it flew for 7 hours, that negates the in-flight fire theory, because fire will usually consume the aircraft or render it inoperable within 30 minutes. I can't think of a single instance where a fire on board sufficient enough to knock out avionics and flight controls was later extinguished and the aircraft saved.
- Depressurization and the effects of hypoxia are beginning to look viable. It might also explain the abrupt change of altitude over time. It does not explain the disablement of the transponders and ADS-B equipment, but perhaps whatever incapacitated the crew was also responsible for the equipment failures.
- On the other hand, an attempted hijacking that ended up in the pilots' incapacitation and no one left to fly the plane or gain access to the cockpit could be possible, but it seems unlikely.
- Where was the aircraft when the Japanese flight last communicated with it (if that story is still true)? I could imagine a scenario where the other pilots were able to communicate (hearing mumbling) because of the advantage of altitude, whereas ATC might not.
- If the aircraft depressurized at some stage, it's possible everyone on board was dead before it hit the water. On the other hand, if it did start flying at a lower altitude, it's equally plausible that some people were alive all the way down, rousing a few hours before the jet ran out of fuel.
- If the debris is as large as the Aussies claim from the satellite imagery (24 meters is one of the larger chunks), it probably ran out of fuel, stalled, and belly-flopped into the ocean. Anyone who may have been alive before it impacted would be dead. On the other hand, if someone were able to control the aircraft into the ocean and it ditched, there may yet be survivors. We can hope for the latter. But expect the worst.
- The Aussies have been oddly interested in the southern Indian Ocean for some time, even before the Rolls Royce data had been fully analyzed. Did they detect the jet on their military radar but aren't willing to report that fact on the merit of keeping their capabilities quiet?
If this lead does not turn up an aircraft, this will remain the mystery of the century. For the sake of the families involved, I do hope there's an end to this to bring them some degree of closure.
