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In a typical FMS architecture including two FMCs, two CDUs and one cross-talk bus when the system operates in the normal DUAL mode, one (1) _____ is the master and the other is the slave. Both (2) _____ exchange data together and synchronise via a cross-talk bus.
  • A
    (1) CDU; (2) FMCS
  • B
    (1) FMC; (2) FMCS
  • C
    (1) FMC; (2) CDUS
  • D
    (1) CDU; (2) CDUS
Refer to figure.
The different modes of operation of the FMS are the following:
  • Dual mode – A modern commercial aircraft usually works in a dual FMS architecture (under normal conditions). In this mode, one FMC is always working as the master and the other as the slave. Both FMCs are synchronized, which means that each performs its own calculations then exchanges data with the other through a crosstalk bus. The master FMC sends its commands to the autopilot, the flight director system, and the autothrottle.
  • Independent mode – Both FMCs are decoupled and there’s ZERO cross-checking between them. This mode is automatically selected by the FMS under certain abnormal conditions such as different database validity on both FMCs.
  • Single mode – When one FMC fails, the remaining one supplies both sides: its onside peripherals and failed FMC’s peripherals.

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