Originally Posted by
BuzzBox
The active FMC synchronises the inactive FMC any time a change is made to the active flight plan or the performance data. When the active FMC fails, the inactive FMC IS ALREADY SYNCHRONISED and ready to assume operation; further synchronisation is not necessary .
Actually, “The active FMCF sends its flightplan data to the inactive FMCF for these conditions:
- Long term power ups
- BITE induced restart
- Flight plan entries and performance data changes.
When the active FMCF fails, a resynchronization (resync) occurs. Resyncs take about 1 second for an entire flight plan update. The active FMCF always resyncs the inactive FMCF. The active FMCF selection is a function of the FMC selector position and FMF partition health.” 777 Training Manual 34-61-00 p106
If the link between both FMCFs in the respective Left and Right AIMS Cabinet is
severed, and the active Left FMCF has failed, a resync is not possible. An auto fail switch is not possible.
A software reset is a function of BITE/fault monitoring. If a software reset should occur, the active route becomes inactive, the performance data is erased, and LNAV and VNAV (if engaged) modes fail. At this time, the crew cannot be using LNAV because it has failed eg diverting to Penang in a chaotic cockpit. The Flight ID has been erased. To regain FMC operation, manually selecting the FMC selector to the right, will make the right FMCF as the active. The crew need to activate and execute the flight plan, enter the necessary performance data, and engage LNAV and VNAV. Now LNAV is available eg tracking west from Penang.
When the SATCOM logged on at 1825:27, the Flight ID was missing.