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Flight Management Computer
Also from: FMC
The FMC is the basis of the FMS. The FMC sends commands to the autothrottle, autopilot and flight director. Map and route information are sent to the DUs. The dual FMC installation is certified as a "sole source" navigation system.
Information entered into either CDU is input to the primary FMC, which then synchronises with the secondary FMC and updates both CDUs. The left FMC is the primary by default.
Functions
The primary FMC is responsible for:
- allocating navaid tuning and updating functions between FMCs
- ensuring synchronisation between FMCs
- controlling CDUs
- providing input to the autopilot
- providing input to the autothrottle
Failures
Electrical
| Power Loss | Effects |
| <10s | LNAV, VNAV disengage data is retained FMC resumes normal operation |
| >10s on ground | all entries must be done again |
| >10s in flight | LNAV, VNAV disengage data is retained SELECT ACTIVE WPT/LEG is displayed on RTE LEGS page |
FMC
| FMC alert light | FMC message light | LNAV, VNAV disengage | VTK on ND | FMC/CDU FAIL light | SINGLE FMC OPERATION message | |
| Left failure |  |  | If AP A | Left | Both | |
| Right failure | | | If AP B | Right | | Both CDUs |
| Both fail | | | | Both | Both | |