Nonetheless, ACARS data proved crucial for gaining an early understanding of Air France flight AF447, which crashed 1 June 2009. Within three days of this aircraft’s disappearance investigators released ACARS data, revealing that the aircraft had transmitted a number of failure reports for various aircraft systems.
ACARS revealed indeed what was going on, on the way down to the ocean. But keep in mind that ACARS data was initially leaked by an AF engineer to the internet and not through official channels. And if you go back in time, AF officials said initially that the ACARS messages proves nothing with regards what happened on AF447. Only month later, everybody was talking about ACARS.
Now with regards to ACARS on B777. Here some insights specific to a B777. B737 for instance is less sophisticated.
ACARS managment Unit (MU) is connected to a 115V BUS and to the 28V Battery BUS (B737/B777)
ACARS MU send over VHF (B737/B777) and over satelite (B777)
ACARS MU collects all vital data of the aicraft (B737/B777)
ACARS MU has downlink (B737/B777) and uplink (B777) connection
ACARS MU connect to each system independantly going over separate BUS (B737/B777)
ACARS MU has two independant, redunant fiberchannels for connecting to mentioned systems below and individual power source (B777). This is the "SAFEBus"
ACARS collect data from: (B737)
Flight Data Unit
FMS
ACARS collects information from: (B777)
Flight Management
Display
Central Maintenance
Airplane Condition Monitoring
Communication Management (including flight deck communication)
Data Conversion Gateway (ARINC 429/629 Conversion
Additional ACARS allows Airline HQ to upload/download data from the EFB (Electronic Fligtht Bag)
With regards to MH370 and ACARS, there are two options
a. Malaysian Airlines offcials are telling us not all they know
b. All ACARS related systems were destroyed immediately, otherwise it would have been sending data as it send over multiple channels.
Cheers
Martin