737 Flight Crew Operations Manual
Flight Management, Navigation -
Flight Management Computer
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
D6-27370-866-EGP 11.32.5
FMC Failure
Single FMC Failure
The FMC/CDU is designed to automatically preserve the most capable modes of
navigation and guidance that can be maintained with the equipment and
navigation aids available. If an error or system failure results in reduced capability,
then the FMC may generate a crew message for display in the CDU scratchpad. If
other system inputs to the FMC should fail, affected CDU displays are blanked to
prevent the display of misleading or erroneous data. For example, loss of the total
fuel input causes some performance related data to be blank. The messages and
FMC internal responses provide an orderly transition from full FMC guided flight
to less automated capability.
If the right FMC fails, the FMC alert light and the FMC message light will
illuminate. The message SINGLE FMC OPERATION will be displayed in both
scratchpads. VTK will display on the right navigation display. LNAV and VNAV
will disengage if autopilot B is in use (can be reengaged if autopilot A is selected).
After 25 to 30 seconds, the right navigation display will display failure
information. The right navigation display may be restored by placing the FMC
source select switch to BOTH ON L.
If the left FMC fails, the FMC alert light will illuminate. The MENU page will
appear on both CDUs. VTK will appear on the left navigation display. LNAV and
VNAV will disengage, but can be reengaged if autopilot B is in use or is selected.
After 25 to 30 seconds, the left navigation display will display failure information.
To restore full operation, the FMC source select switch must be moved to BOTH
ON R.
Note: During an FMC software restart, the navigation display map track may
rapidly slew to 0 degrees then to the correct value.
Dual FMC Failure
If both FMCs fail, the FMC alert light will illuminate. The MENU page will
appear on both CDUs. VTK will appear on both navigation displays. LNAV and
VNAV will disengage. After 25 to 30 seconds, both navigation displays will
display failure information.
Software Exception Handling Logic
Note: A Software Exception is the disruption in the normal flow execution of the
software code; i.e. an attempt to solve an unsolvable map calculation.
September 15, 2016
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