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747-400 MAINTENANCE MANUAL
2) Once synchronization is complete, the FCC initiates a pre-engage test. The test verifies that the Modular Avionics and Warning Electronics Assembly (MAWEA) is functioning properly to avoid a false warning upon engagement. A similar test is also run for battery warning.
(d) Upon sucessful completion of the pre-engage test, the ENGAGE solenoid is engergized and the engage pistons are clamped to the output crank smoothly.
(2) Multi-Channel Engagement
(a)
Multi-channel engagement is similar to single-channel engagement. There are the engage request, arm (synchronization and pre-engage test) and engage phases as in single channel engagement. In addition, logic is provided to determine FIRST IN COMMAND and FOREIGN channels to set priority command sequence for channel failure or returning to single channel operation.
(b)
After selection of APP mode, the off-line channels (those not engaged) are automatically armed. While armed, the FCCs synchronize to their respective EASs. Synchronization for multi-channel operation is identical to the synchronization process for single-channel operation. Pre-engage test are also run during multi-channel arm as they are are for single-channel arm. The pre-engage test run for single-channel is also run for multi-channel. In addition, the following pre-engage test are performed during multi-channel arm: 1) Detent comparator test - servo position is compared to
surface position to detect detent piston failures.
2) Bus isolation monitor - detects the failure of the power system to isolate the power sources, thus failing to provide for independant channel operation.
3) Servo synchronization test - verifies that each EAS is synchronized to its respective surface prior to the end of the pre-engage testing.
(c) After the pre-engage tests have passed, the off-line channel(s) will engage if glideslope and localizer have been captured, and the airplane is below 1500 feet.
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MAINTENANCE MANUAL
B. Pitch Channel Engage Logic
(1)
In each of the three phases of engagemnet there are various parameters that are monitored. When an engage request is initiated, the FCC hardware and software monitors determine if the request can be implemented.
(2)
Once an engage request is received, the pitch channel will be inhibited from being armed if any of the following conditions exist:
(a)
MCP interface failure
(b)
Any foreign channel detected to have a solenoid energized (single-channel operation)
(c)
Power monitor failure
(d)
FCC internal failure
(3)
Once the pitch channel is armed, it will fail to engage and transition from ARM to OFF, if any of the following conditions exist:
(a)
EAS loop failure
(b)
EAS LVDT failure
(c)
EAS not synchronized to surface position
(d)
EAS engage solenoid energized
(e)
No program pin parity valid
(f)
FCC memory failure
(g)
FCC self-test (pre-engage) failure
(h)
If NOT multi-channel arm, energized rudder solenoid detected
(i)
If multi-channel arm, any two of the same autoland sensors for two different channels fail
(4)
The pitch channel will disengage (transition from CMD to OFF) if any of the following exist:
(a)
FCC failure
(b)
Power monitor failure
(c)
Altitude capture or hold functions cannot be performed
(d)
Pitch servo loop failure
(e)
If NOT in multi-channel engage, rudder servo is detected to be engaged
(f)
If NOT in multichannel engage, foreign servo engaged
(g)
If NOT in multi-channel engage, air data stability signals not valid for 7 seconds
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