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side of the APU enclosure.
Heat Shield
The exhaust gas heat shield is installed on the aft side of the fuselage, below the right engine
pylon. The heat shield is used to minimize the exhaust gas impact on the aircraft skin.
EGT Indications
APU exhaust gas temperature is represented on the EICAS page, using a grey legend (EGT)
and a digital readout that is displayed in degrees Celsius. The APU’s operating limits are
represented by color change of the EGT readout by showing green, yellow and red when the
APU temperature increases.
AUXILIARY POWER UNIT
Description
Vol. 2 05−10−6
Oct 05/06
CL−605 Flight Crew Operating Manual
PSP 605−6
AIR INTAKE AND EXHAUST (CONT'D)
Air Intake, Exhaust and Indication
Figure 05−10−4
AUXILIARY POWER UNIT
Description
Vol. 2 05−10−7
Oct 05/06
CL−605 Flight Crew Operating Manual
PSP 605−6
APU FUEL DISTRIBUTION
Description
The APU fuel system provides fuel for APU start, acceleration, and governed speed control.
During start, the fuel system provides the correct amount of fuel to support combustion, and
ensures smooth acceleration of the engine to full power. Once full power is reached, fuel flow is
modulated, as necessary, to meet the demands of varying pneumatic and electrical loads, while
maintaining a constant speed.
The normal fuel supply to the APU is from the right main tank. A backup fuel supply from the left
engine motive flow system is provided in case negative-G conditions are encountered.
Components and Operation
APU Fuel Pump
The DC battery bus powers the APU fuel pump, which draws fuel from the right main tank. The
pump provides fuel to the fuel control unit through the APU’s feed line and the fuel shutoff valve.
A portion of the fuel from the APU fuel pump is directed to the APU fuel control unit for
combustion, while the remainder is routed through the fuel/oil heat exchanger to provide cooling
of the APU generator adapter oil. Fuel that has passed through the fuel/oil heat exchanger is
returned to the right main tank.
Selection of the APU PWR FUEL switch/light activates the APU fuel pump. This selection also
opens the APU’s fuel shutoff valve and negative-G shutoff valve. Insufficient APU fuel pump
output pressure is indicated by an APU PUMP caution EICAS message, and illumination of the
PUMP FAIL switch/light legend on the APU panel.
APU Fuel Shutoff Valve
The APU fuel shutoff valve (SOV) opens when the PWR FUEL switch/light is pressed in, and
closes when it is pressed out. If the valve does not match the switch position within 5 seconds,
an APU SOV caution EICAS message is displayed.
When the APU FIRE PUSH switch/light is pressed in, the APU fuel shutoff valve and the APU
negative-G shutoff valve close. Successful closing of the valves is indicated by an APU SOV
CLSD advisory message, and illumination of the green SOV CLOSED switch/light legend on the
APU panel. If the APU SOV fails to close after APU FIRE PUSH switch/light selection, an APU
SOV caution message is displayed.
AUXILIARY POWER UNIT
Description
Vol. 2 05−10−8
Oct 05/06
CL−605 Flight Crew Operating Manual
PSP 605−6
APU FUEL DISTRIBUTION (CONT'D)
APU Fuel Pump and Shutoff Valve
Figure 05−10−5
APU Fuel Control Unit
The APU fuel control unit (FCU) is driven by the accessory gearbox, and meters fuel to the
combustor under command of the electronic control unit (ECU). The APU fuel control unit is
equipped with an internal solenoid-operated fuel shutoff valve that is commanded open and
closed by the APU ECU, controlling fuel to the APU fuel control unit. In addition to controlling
fuel shutoff, the ECU regulates fuel flow output from the fuel control unit, ensuring proper APU
operating speed and temperature ranges.
AUXILIARY POWER UNIT
Description
Vol. 2 05−10−9
Oct 05/06
CL−605 Flight Crew Operating Manual
PSP 605−6
APU FUEL DISTRIBUTION (CONT'D)
During normal or automatic APU shutdown, a simulated overspeed signal is generated within
the ECU, commanding closure of the fuel control unit’s solenoid shutoff valve. Closing this valve
causes an isolation of fuel supply to the APU’s fuel control unit, resulting in APU shutdown.
APU Negative-G Shutoff Valve
The APU negative-G shutoff valve opens and closes when the PWR FUEL switch/light is
pressed. If the valve fails to close when the PWR FUEL switch/light is pressed out, the APU NEG
G SOV caution message is displayed.
If a negative-G condition exists or the APU fuel pump fails, a one-way check valve, that
　
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