Originally Posted by
Ian W
Bilby, Desparing Traveller et al,
ACARS "was deliberately turned off" was reported early on. Now ACARS 'logs on' and 'logs off' ....
The repeated statements that someone had "switched ACARS off" rather than we received no more ACARS transmissions after the last one at cruise, implies that there is evidence of a tidy log-off.
I don't think there is any 'Official' statement that ACARS was switched off or logged off. I believe the position/time of last ACARS on the various plots is that of a complete and normal ACARS transmission and there is no indication of a log off ACARS message.
The log ons at 18:25 (from memory) and the 7th ping, are the satellite communication system itself, not the ACARS communications. Further, I believe it is established fact that MH370 was not configured to have the ACARS system use the satcom link, Satcom was only onboard to provide telecommunications for Business/First class (and potentially available to the flight crew for calls).
I have little technical knowledge of the ACARS system, but it appears to not intrinsically require a log on/log off process. It seems to just be a VHF/HF/Satcom store and forward system where individual data packages are sent to the central service for storage and then periodically polled or pushed until an ACK is received or a retry limit is hit.
It is also not clear to me that the Satcom system itself has any 'logoff' function and therefore if there would be anything to distinguish between the device being turned off/ put into standby/ loosing power/ being destroyed