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EFFECTIVITY
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
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APU CONTROLS - ELECTRONIC CONTROL UNIT - FAULT MONITORING
APU CONTROLS - ELECTRONIC CONTROL UNIT - FAULT MONITORING
EFFECTIVITY
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
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APU CONTROLS - ELECTRONIC CONTROL UNIT - FAULT MONITORING
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D633A101-GUN Oct 10/2005
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
General
The ECU makes sure the APU operates correctly. If the ECU
senses APU operation that could cause damage, the ECU shuts
down the APU. This is a protective shutdown. A protective
shutdown can occur anytime during APU start and operation.
The ECU keeps protective shutdown data in memory. You use
the CDU to get this data.
The ECU makes the maintenance light on the AC systems,
generator and APU module come on if the APU requires
servicing or maintenance. You can use the APU with the
maintenance light on.
Protective Shutdown
The ECU uses protective shutdown logic to automatically
shutdown the APU. You know the ECU did a protective
shutdown if the fault or overspeed lights come on. The ECU
also does a protective shutdown and the low oil pressure (LOP)
light comes on if oil pressure is too low when the APU speed is
more than 95%. These lights are on the ac systems, generator,
and APU module. When the ECU does a protective shutdown,
the master caution and APU annunciator light on the P7 panel
also come on.
The APU protective shutdown lights go off when you move the
APU switch to OFF and back to ON with APU speed less than 7
percent or when the ECU deenergizes. The ECU deenergizes
five minutes after these condition occur:
* APU switch in OFF position
* APU CDU BITE is off
* APU fuel shutoff valve is closed.
If the fuel shutoff valve fails in the open position, the ECU will not
deenergize. This causes the FAULT light to be on until you
move the battery switch to the off position.
These are the protective shutdowns that cause a fault light:
* APU fuel valve shutdown
* DC powerloss shutdown
* ECU shutdown
* Fire shutdown
* Inlet door shutdown
* Inlet overheat shutdown
* Loss of EGT shutdown
* Loss of speed shutdown
* No acceleration shutdown
* No APU rotation shutdown
* No flame shutdown
* Oil filter shutdown
* Oil temperature shutdown
* Overtemperature shutdown
* Reverse flow shutdown
* Sensor failure
* Underspeed shutdown.
These are the protective shutdowns that cause an overspeed
light:
APU CONTROLS - ELECTRONIC CONTROL UNIT - PROTECTION SYSTEM
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
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* Overspeed shutdown
* Overspeed protection.
A low oil pressure protective shutdown causes the low oil
pressure light to come on.
During a protective shutdown, these APU and airplane system
changes occur:
* Fuel solenoid valve closes
* Fuel control unit metering valve closes
* APU light comes on
* Remove ready to load signal (RTL)
* Igniter deenergizes, if energized
* IGVs close
* SCV opens
* APU fuel shutoff valve closes
* APU inlet door closes.
The fuel shutoff valve and inlet door start to close when the APU
speed decreases to 30 percent on all shutdowns except FIRE
and OVERSPEED. The fuel shutoff valve and inlet door begin to
close as soon as a FIRE or OVERSPEED shutdown begins.
Protective Shutdown Logic
An APU fuel valve shutdown occurs if the ECU commands the
fuel shutoff valve closed and the ECU does not get a closed
signal 29 seconds after the command. This fault makes the
FAULT light come on and stay on until the fuel valve closes or
you put the battery switch to the OFF position.
A DC powerloss shutdown occurs if ECU power is lost for more
than 50 msec and APU speed is more than 7 percent.
An ECU shutdown occurs when a failure of any ECU component
that does not let the ECU detect or control APU operations. An
example of this is a failure of the fuel torque motor driver.
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