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REV 76, Jul 17/09
CL−604 Operating Manual
PSP 604−6
START AND IGNITION (CONT'D)
APU Normal Shutdown
Figure 05−15−9
AUXILIARY POWER UNIT
Description APU 150
Vol. 2 05−15−17
REV 76, Jul 17/09
CL−604 Operating Manual
PSP 604−6
START AND IGNITION (CONT'D)
Protective Shutdowns
The ECU automatically shuts down the APU when certain fault conditions are detected.
Automatic protective shutdowns occur for the following pre-programmed conditions:
Protective Shutdown Table
CONDITION EICAS INDICATION
FIRE
Master warning, fire bell, APU fire light,
APU FIRE warning message
OVERSPEED
Master warning, triple chime,
APU OVERSPEED warning message
OVERTEMP
Master warning, triple chime,
APU OVERTEMP warning message
LOW OIL PRESSURE
Master caution, single chime,
APU OIL PRESS caution message
HIGH OIL TEMPERATURE
Master caution, single chime,
APU OIL TEMP caution message
GENERATOR ADAPTER LOW OIL PRESSURE
Master caution, single chime,
APU OIL PRESS caution message
GENERATOR ADAPTER HIGH OIL TEMPERATURE
Master caution, single chime,
APU OIL TEMP caution–message
LOSS OF EGT SENSOR EGT digital readout dashed
UNDERSPEED
RPM readout/pointer (speed below 80% longer than
5 sec)
ECU FAIL Loss of EICAS display for the APU
APU Fault Panel
Specific faults that cause APU shutdown are annunciated on the APU FAULT panel by solid
state LEDs. This panel also includes an IND RESET button to clear all LEDs following
rectification of the fault(s).
If necessary, an emergency shutdown of the APU may be accomplished by using the APU
STOP button, located on the APU FAULT panel. When the APU STOP button is used, the APU
FAULT indicator shows a faulted condition.
Following a protective shutdown or activation of the APU stop switch, the APU control panel
switch/lights must be pressed out before the APU can be restarted.
AUXILIARY POWER UNIT
Description APU 150
Vol. 2 05−15−18
REV 76, Jul 17/09
CL−604 Operating Manual
PSP 604−6
START AND IGNITION (CONT'D)
APU Protective/Emergency Shutdowns and Faults
Figure 05−15−10
AUXILIARY POWER UNIT
Description APU 150
Vol. 2 05−15−19
REV 76, Jul 17/09
CL−604 Operating Manual
PSP 604−6
PNEUMATIC SUPPLY
Description
APU compressor bleed air is used to pressurize the left side of the 10th-stage bleed air manifold,
providing pneumatics for engine starting and air conditioning. Reverse airflow protection from the
main engines into the APU is provided by a one-way check valve and the 10th-stage bleed air
switch/lights interlock control logic (Refer to Chapter 18, Pneumatic System, for additional
information on the 10th-stage interlock circuit).
The APU pneumatic control system consists of two main components: the load control valve (LCV)
and the surge control valve (SCV).
Components and Operation
Bleed Air Supply
The APU delivers a portion of its compressor discharge air to the 10th-stage manifold when the
LCV is opened. This diversion takes pneumatic energy from the turbine, and some of the
cooling air from the APU’s combustion system. As with shaft loads, the rpm drops, and the APU
recovers full governed speed by commanding an increase in fuel flow. The loss of pneumatic
energy is replaced with thermal energy (fuel), and EGT increases.
Two variables influence EGT under bleed load conditions:
• Aircraft demand for bleed air (air conditioning packs or engine starting)
• Ambient air temperature and air density
If the EGT reaches its operating limit, the ECU reduces the bleed air load by commanding the
LCV to cycle toward the closed position.
Load Control Valve
The APU LCV is located above and to the right of the APU turbine section. The valve is
controlled by the APU ECU when the APU LCV switch/light on the BLEED AIR panel is selected
to the open position. The LCV controls APU bleed air supply to the left side of the 10th-stage
manifold. The ECU ensures that system priority is given to electrical loads over the bleed air
demand, by cycling the LCV closed (reducing bleed load) when the exhaust gas temperature
approaches operating limits.
Load control valve operation is indicated by illumination of the OPEN legend of the APU LCV
switch/light. When the ECU cycles the LCV for EGT limit protection, the OPEN legend
extinguishes. If the APU LCV has failed open with the 10th-stage switch/light interlock protection
activated, the APU LCV FAIL caution message is displayed on EICAS and the FAIL legend
　
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