Originally Posted by
Ian W
ACARS was only licensed and activated on VHF by the Malaysians it was not linked to INMARSAT SATCOM or to Boeing or Rolls Royce health monitoring. So the ACARS logon/logoff would be an ARINC/SITA protocol over VDL which I believe is ARINC 622 'ATS Data Link Applications over ACARS, or 618 Air/Ground Character-Oriented Protocol Specification.
Ian,
two points.
1 - I can't see described in any of the protocols a logoff message (nor for that matter a log on) at the ACARS level (i.e. a message that would indicate that the ACARS system was logging off, rather than that the underlying transport layer was logging off). Equally, I am certain that the VHF transport layer does not log on or logoff as it is just open radio spectrum.
People have speculated the authorities have some indication the ACARS was 'logged off in a conscious deliberate way'. I can see no basis in the technology being used that would allow that possibly to be concluded with respect to the ACARS system. As such, I believe it is certain to have been a turn of phrase used by someone in an early briefing rather than anything relevant.
2 - People have represented that Malaysian Airlines did not use the satcom for ACARS, yet the official preliminary report declares it did, and that the 1:07 ACARS message was transmitted via satcom link, and finally, there is a satcom message originating from the aircraft at just before 1:07 and finishing just after 1:07.
Originally Posted by Preliminary Report
It was later established that the transmissions from the Aircraft Communication and Reporting System (ACARS) through satellite communication system occurred at regular intervals starting before MH 370 departed Kuala Lumpur, Malaysia at time 12:56:08 MYT and with the last communication occurred at 01:07:49 MYT.
I had originally assumed the attribution of link layer (satcom vs VDL) was an error. However, at this remove, if it was an error, it would have been corrected. Also, it exactly matches the timing of the Inmarsat final packet acknowledgement from the aircraft (to the exact second).
I therefore believe, subject to some conclusive evidence of MA non-use of Satcom for ACARS, that MH370 was using Satcom as its ACARS link layer. And therefore, the reason we have no VDL ACARS logs for MH370 is because it wasn't using VDL, not because they exist but have not been released.