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FMGS
Also from: Flight Management Guidance and Envelope System; FMGES
Consists of:
Dual mode
Whichever AP or FD is on, that FMGC becomes master, unless both sides are on in which case FMGC 1 is master. The A/THR is driven by the master FMGC. If both FDs are on, each FMGC drives its onside FD and FMA on the respective PFD.
Independent mode
Occurs when the cross-talk bus is lost. An 'INDEPENDENT OPERATION' message is displayed on each scratchpad. Each FMGC drives its own FG, EFIS, and MCDU. Entries must be made on both MCDUs.
Single mode
Occurs when 1 FMGC fails. The onside ND displays MAP NOT AVAIL, and the FM1 or FM2 annunciator on the onside MCDU illuminates. After the FM source selector is set, an OFFSIDE FM CONTROL annunciation is displayed on the onside ND. The FMAs display 2FD2 (FMGC 1 failure) or 1FD1 (FMGC 2 failure) indicating that the FD bars on both PFDs are driven by the same FMGC.
On the STATUS page, AP1(2), FM1(2), and CAT 3 DUAL are displayed as inoperative systems, and CAT 3 SINGLE ONLY is displayed. FM SWTG is displayed on the ECAM.
Back up navigation mode
Occurs on a dual FMGC failure. NAV B/UP prompts appear on each MCDU. Managed modes are not available. Each MCDU uses a backup flight plan it has stored internally. Messages on the STATUS page are MCDU BACK UP NAV AVAIL and CAT 1 ONLY (due to loss of DH display). The AP and FD may still be available if the FG part of the FMGC is not lost.