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Shutdown
After cooldown, the APUC does a test of the overspeed shutdown circuits to shut down the engine. The APUC sends a signal to the fuel shutoff solenoid valve and to the torque motor on the fuel metering valve to stop fuel flow. The APU speed then starts to decrease.
At 15 percent RPM, the air inlet door begins to close and the APU fuel shutoff valve in the left wing tank closes.
The APU speed decreases to zero.
Training Information Point
15 seconds after you move the APU selector to the OFF position, the APU COOLDOWN memo message shows. This message goes out of view after 90 seconds.
If you move the APU selector to the ON position during APU cooldown (less than 105 seconds after the selector is moved to OFF), the APU will accelerate to 100 percent and continue to operate.
If you move the APU selector to the ON position after the cooldown period has ended (more than 105 seconds after the selector is moved to OFF), the APU shutdown will continue.
EFFECTIVITY BEJ ALL  49-00-00 
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777 AIRCRAFT MAINTENANCE MANUAL

AUXILIARY POWER SYSTEM -NORMAL SHUTDOWN

EFFECTIVITY BEJ 001-004  49-00-00 
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777 AIRCRAFT MAINTENANCE MANUAL

AUXILIARY POWER SYSTEM -NORMAL SHUTDOWN

EFFECTIVITY BEJ 005-999  49-00-00 
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D633W101-BEJ  Sep 05/2003 

AUXILIARY POWER SYSTEM -PROTECTIVE SHUTDOWNS

General
The APUC controls the automatic protective shutdown of the APU. If the APUC finds some APU conditions or faults, it sends a protective shutdown signal.
There are two modes of APU automatic shutdown protection, the attended mode and the unattended mode.
Attended Protective Shutdown
The attended mode operates when at least one engine is running or if the aircraft is in the air. These conditions will cause a protective shutdown in the attended mode:
*
APU overspeed (more than 106 percent RPM)

*
Loss of overspeed protection (loss of the two overspeed protection circuits)

*
APU compartment fire

*
APU inlet fire/load compressor reverse flow (T2 > 177C)

BEJ 001-004
* Load compressor Low flow (pressure sensors show low flow condition)
BEJ 005-999
* Load compressor Low flow (surge control valve does not follow command and pressure sensors show low flow condition)
BEJ ALL
*
APU speed droop (RPM less than 88 percent and no acceleration for 10 seconds)

*
APUC internal failure

EFFECTIVITY
BEJ ALL

*
Loss of power to the APUC

*
Air inlet door closes (air inlet door position switch indicates door closed, which occurs at 70 percent of full open position).

Unattended Protective Shutdown
The unattended mode operates when the main engines are not running and the airplane is on the ground. This mode supplies protective shutdown for all of the attended mode conditions plus these conditions:
*
Low oil pressure (less than 35 psi)

*
Loss of oil pressure signal (from both the pressure sensor and the low oil pressure switch)

*
High EGT (calculated turbine inlet temperature is above 1288C)

*
Loss of EGT signal (from both thermocouple rakes)

BEJ 005-999
* Generator scavenge filter is clogged
BEJ ALL
* High oil temperature (more than 156C).
Indication
All protective shutdowns cause the APU SHUTDOWN advisory message to show and turn on the APU fault light on the P5 overhead panel. The APU status message also shows when there is a protective shutdown. In the attended mode, these conditions cause the APU LIMIT caution message to show:
*
Low oil pressure

*
High EGT

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AUXILIARY POWER SYSTEM -PROTECTIVE SHUTDOWNS
* High oil temperature.
Training Information Point
You can attempt to restart the APU after you move the APU selector to OFF to unlatch the protective shutdown.
EFFECTIVITY BEJ ALL  49-00-00 
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D633W101-BEJ  May 05/2003 

 

AUXILIARY POWER SYSTEM -PROTECTIVE SHUTDOWNS

EFFECTIVITY BEJ 001-004  49-00-00 
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D633W101-BEJ  Sep 05/2003 

 

AUXILIARY POWER SYSTEM -PROTECTIVE SHUTDOWNS

EFFECTIVITY BEJ 005-999  49-00-00 
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D633W101-BEJ  Sep 05/2003 

AUXILIARY POWER SYSTEM -INDICATIONS

General
The status display and maintenance page show APU system data.
Status Display
　
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