Flight management system back-up navigation for the A330/A340 aircraft

Presents the architecture and functional operation of the multi-purpose control display unit (MCDU) back-up navigation used on the A330/A340 MCDU aircraft. Its purpose and capability in playing a key role on the A330/A340 for providing navigational back-up and equipment redundancy are explored. The A330/A340 flight management system is embedded in two flight management and guidance and envelope computers (FMGECs) and the triple redundant MCDU. At any one time two of the MCDUs are used to interface with the two FMGECs. The third MCDU can be switched into either position in case of an MCDU failure. In addition, two of the MCDUs have the capability to provide back-up navigation in case of loss of the FM function from the FMGECs