787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Engines, APU -
APU System Description
Copyright © The Boeing Company. See title page for details.
D615Z003-TBC 7.30.3
APU Automatic Start
In flight, if three or more engine generators go offline, the APU automatically
starts, regardless of APU selector position. When the automatic start condition is
no longer valid, the APU can be shut down by positioning the selector to ON, then
OFF. When the automatic start condition is valid, the APU can only be shut down
by pulling the APU fire switch.
APU Shutdown
When the APU selector is rotated to OFF, the APUC initiates a normal shutdown
sequence. The APU continues running in a two minute cooldown cycle. The
EICAS memo message APU COOLDOWN is displayed. At any time during the
cooldown period, the APU may be returned to its running condition by placing the
APU selector back to ON. When the cooldown period finishes, an APU overspeed
condition is simulated to test the overspeed and fuel shutoff protection. This shuts
off fuel and the APU shuts down. The APUC then commands the APU spar valve
to close and the CCS fuel management application turns off fuel pumps as
applicable. At 15% rpm, the APUC commands the air inlet door to close and the
normal shutdown sequence is complete.
APU Operating Modes
The APU has attended and unattended operating modes. The attended mode
operates when either engine is starting or running, or when the airplane is in flight.
The unattended mode operates in all other configurations on the ground.
APU Attended Mode
In the attended mode, any of the following faults cause the APU to shut down
immediately:
• APU fire/inlet overtemperature
• overspeed/loss of overspeed protection
• APU controller failure
• speed droop
• APU start failure (no rotation, or no acceleration, or no light-off)
• Air inlet door failed closed
There is no cool down period. The EICAS advisory message, APU SHUTDOWN,
displays.
For the following faults, the APU continues to operate and the EICAS caution
message APU LIMIT displays:
• high EGT
• high oil temperature
• low oil pressure
February 13, 2009
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