Originally Posted by
DespairingTraveller
I was a bit surprised to read that paragraph, as I had been under the impression that ACARS was VHF only on this flight. Like others, I've also been under the impression that the 1:07:49 message was a routine engine report.
I suspect that the report conflates the Satcom infrastructure (which logged twice in flight, and is the source of the pings), with the ACARS system (which provides store and forward text and data messaging from the flight deck and various aircraft systems). But ultimately, it is irrelevant in that we know when the last ACARS message was transmitted and we know the Satcom infrastructre was connected for many hours after that.
IanW,
Understood - My point was more on the logoff side. It doesn't appear that either system (SatCom or the ACARS store/forward network) have any intrinsic need to have a logoff function. From those with more technical knowledge, is there a logoff message the would or would not be expected in certain circumstances?
I have believed that both are like a transponder in that you know it is not 'on' when it stops responding/sending rather than something like a logout messaging being sent. As such, it is not possible to to deduce the 'Why' from a loss of ACARS or Satcom (or transponder) data. It is intinguishable between the device being shut down in a controlled way (i.e turned off in the normal way), suddenly issolated from power, failed, or destroyed.