Reconciling WSJ and Malaysia news briefing by tracing ACARS data path
I posted in the previous thread that I assume MH
uses SITA as Service Provider for ACARS.
In that case, data transmission could be:
- via VHF to ground stations, then probably sent encrypted via Internet VPN to a central site where the data is filtered and routed to specific destinations
- through the global beam of the Inmarsat4 satellite that covers the region: that means down to the Inmarsat earth station, processed there, then sent as before to a central site for dispatching
- through an Iriidum LEO satellite, across to neighbouring Iridium satellites and so forth until it reaches an Iridium satellite in view of the main earth station near Washington DC.
No matter what path is used, the raw messages will go to one data center, probably a SITA facility in Switzerland (?).
From there, messages are filtered and routed to their specific destination e.g. Derby in the UK for RR
Depending upon the over-the-air method used by MH370 we can say that:
- if VHF was used, then SITA knows within at most a 300km radius (much smaller at a low altitude) where the airplane was when it transmitted its report. SITA has many VHF ground stations in Asia and that should always be a first choice before satellite is used.
- if Inmarsat 4 was used, technically some raw messages may have reached the earth station without necessarily being forwarded to SITA and others, including Malaysia
- if Iriidium was used, selective filtering before SITA is then even simpler (under US control), if one would like to intercept extra but undocumented data reports sent by aircraft.
Therefore, it is technically possible that both WSJ and Malaysia are truthful.