Malaysian Airlines MH370 contact lost

[MrPeabody]

ACARS Datalink Sub-function

There has been a lot of discussion around ACARS and SATCOM. Some info below on the Data Communications Module function.

"The DCMF supplies the airplane part of ACARS. The ACARS sub-function controls air/ground file transfers and onboard message routing. The message routing process supplies uplink message routing to onboard systems. It downlinks message routing to the ACARS ground service providers (GSP) through a VHF transceiver (Post SB) or through VHF or SATCOM (Pre SB). The ACARS datalink sub-function uses information within each uplink to send the message to the applicable system. The ACARS datalink sub-function also routes downlinks to the path set by the flight deck crew and airplane systems.
The flight crew sets the datalink path through the MANAGER menu of the AIMS flight deck communications function (FDCF). The path preferences are:
VHF
SATCOM (Pre SB)
Auto."

As you may not be aware a lot of operators do not have ACARS through SATCOM and have modified it out of this vintage of B777's; I believe MAS is one of them.

The satellite handshakes were produced through Classic Aero connections for voice communication and satellite telephone.

My guess is that every time there was a major course correction the beam steering unit in the SATCOM was trying to retune the RF signal to keep track with the satellite. This would explain all the pings under 1 hour; = change in course.