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Manually selected ON and anti-ice is active.
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The left engine pressure regulating valve is open.
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The right engine pressure regulating valve and the crossbleed valve are open.
GF0510_007
Volume 2 Flight Crew Operating Manual Rev 3, Apr 25, 2005
ECU COMPONENT CONTROL SCHEMATIC (CONT'D)
Pneumatic (Cont’d)
A Surge Control Valve (SCV) works to protect the APU compressor from a potential to Surge (stall). The solenoid valve assembly (which allows pneumatic air to open the SCV) is energized only when:
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The APU generator is providing electrical power and
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The APU LCV is CLOSED (APU not supplying any bleed air to the ECS) and
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Atmosphere pressure of 7 psia is sensed (at and above 16,375 during ISA conditions)
The exaust of the APU SCV is located on the left side of the fuselage, aft of the engine pylon. The operation of the SCV is transparent to the pilot.
Rev 3, Apr 25, 2005 Flight Crew Operating Manual Volume 2
AUXILIARY POWER UNIT
APU SYSTEM OPERATING MODES
The APU system operating modes are as follows:
ECU Power-up
The ECU enters a power-up mode when the airplane BATTERY MASTER switch is selected to ON. It does a test of its circuitry to verify that it is capable of executing the APU control requirements for operation.
Start Mode
Upon receiving an active start signal and successful completion of the pre-start test sequence, the FADEC will initiate an APU start. During the start mode, the FADEC activates the fuel request signals, positions the APU door, activates and/or deactivates the starter and ignition control systems. It also controls fuel flow as a function of timed acceleration and EGT schedule as the APU accelerates to 100 percent.
On-speed Mode
When the APU reaches 95 percent speed, the FADEC transitions to the On-speed Mode to control governed speed and load control activation.
Cooldown Mode
With the APU operating in the On-speed Mode, the FADEC transitions to the Cooldown Mode when the APU switch is selected OFF. Upon entering this mode, the load control valve is closed and the ready to load signal is removed. During cooldown, the APU speed is lowered to 70% RPM for 60 seconds below 20,000 feet or remains at 100% RPM for the 60 second cooldown above 20,000 feet.
Shutdown Mode
Upon completion of the cooldown period or in the event of a protective shutdown, the FADEC transitions to the Shutdown Mode and controls the APU shutdown sequence.
APU SYSTEM OPERATING SEQUENCE
The following events occur when the APU is selected from RUN to START position:
APU Starting
The APU can operate with battery power only. The APU is started automatically when the START switch on the APU control panel is selected and held for one second. The RUN position commands the APU fuel SOV and right DC auxiliary pump to energize. The START position is spring loaded to RUN from the start position. When the door is correctly positioned, the FADEC engages the starter. When the speed reaches 5%, fuel and ignition are activated. At 50% speed, the starter disengages. For ground starts, ignition is deactivated at 50%. In flight, ignition is deactivated at 98%.
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