May I please just clarify from one who operates the equipment commercially and has flown for 35 years:
- With the sole exception of the 'handshake' pings no information has come from the aircraft. The only other information on the flight may be the primary radar information and the accuracy and interpretation may be suspect.
- The transponder may have been turned off or may have failed but there is no way of knowing which.
- Pilots cannot turn off the ACARS from the flight deck. If you doubt this ask one who flies a B777 or perhaps explain why I am wrong?
- There was no position, altitude or speed information transmitted to the ground after the incident. The only way that may happen is through the transponder (off/failed) or CPDLC. CPDLC would not have been used on this sector as KL and Vietnam do not use it.
- The 'ACARS' does not transmit any flight plan information that the pilots may have programed into the FMC. CPDLC does so through the ACARS but CPDLC was not used. There is no way of knowing what was in the plan or changes.
All of these theories of hijack/interference/crew involvement appear to be based on information that the aircraft did not and could not transmit. They came from officials listening to pilots, misunderstanding and trying to look important by telling the media inaccurate information and the media then happily published it.