3. B.
(5) Monitors
The flight guidance computers incorporate internal monitors that are
designed to disconnect the system (if only one FGC is valid) or
automatically switch to the second FGC (if two FGCS are valid) when
a fault is detected.
When a fault is detected, the bad FGC will
automatically force itself invalid (EICAS will annunciate FGC 1 FAIL
or FGC 2 FAIL).
After an FGC has detected a fault, it goes invalid. It will then
automatically initiate a self-test. If this self-test passes, the
(5.1)
FGC
will becbme valid again (the EICAS
automatically clear). This process of
self-test after a detected fault is ca”
time required for the monitor recovery
if the cross-channel
FGC is valid, or ~
cross-channel
FGC is invalid (-905 FGC
FGC FAIL message” would-
automatically initiating a
led monitor recovery. The
to be performed is 7 seconds
5 seconds if the
only).
Monitor recovery is initiated automatically except when a fault is
detected with only one FGC valid.
In this case, the pilot must
initiate the monitor recovery action by depressing either the pilot
or copilot quick disconnect switch.
Prior to an FGC forcing itself invalid, the FGC writes the fault
data into memory.
This data may be retrieved by accessing the
flight fault summary section of the AFGCS test when performing the
ground maintenance test.
The instructions for the ground
maintenance test are provided in section 4.
Monitor recovery is enabled
in all modes except VOR/BC/LOC track
modes.
If an FGC detects a fault when in one of these modes,
monitor recovery will not occur until after the track mode is
cancelled.
As long as both FGCS are valid when a fault is detected,
there will be no loss of the active mode because the remaining FGC
would automatically perform all the functions that were being
performed by the failed FGC.
If a particular fault results in an FGC performing monitor recovery
more than once in a 45-second period, the FGC will force itself
invalid and will not perform additional monitor recovery attempts.
Power Interruptions
Figures 257 and 258 illustrate the engage timing requirements for
various power interruptions and AFCS fault conditions.
22-14-00
Page 298.82
Apr 15/93
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