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787 Flight Crew Operations Manual
Engines, APU -
Engine System Description
Boeing Proprietary 7.20.15
The EICAS caution message ENG THRUST (L or R) is displayed if:
• actual thrust is significantly less than or more than commanded thrust
• actual thrust is not increasing or decreasing to commanded thrust, and
• airspeed is V1 or greater.
787 Flight Crew Operations Manual
Engines, APU -
Engine System Description
7.20.16 Boeing Proprietary
Intentionally
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787 Flight Crew Operations Manual
Engines, APU Chapter 7
APU System Description Section 30
Boeing Proprietary 7.30.1
7.30 Engines, APU-APU System Description Introduction
The auxiliary power unit (APU) is a self–contained gas turbine engine located in
the airplane tail cone.
The APU can be started and operated to the airplane maximum certified altitude.
The APU supplies electrical power. Electrical power is available throughout the
airplane operating envelope.
Refer to the following chapters for additional information:
• Chapter 6, Electrical, for a description of APU electrical operation
• Chapter 8, Fire Protection, for a description of the APU fire protection
system
• Chapter 12, Fuel, for a description of the APU fuel system.
APU Operation
APU Start
The APU is started by either the left or right APU Starter Generator (ASG).
Each ASG is powered by forward external power or Variable Frequency Starter
Generator (VFSG) power. The right ASG is also powered by the APU battery or
right aft external power. The APU battery powers the air inlet door and the main
airplane battery powers the fuel valve, DC fuel pump, and fire detection system.
Starter selection is automatic. The right ASG is the primary APU starter.
Rotating the APU selector to START begins the automatic start sequence.
APU fuel is supplied from the left fuel manifold by any operating AC fuel pump
or the DC fuel pump. With AC power available and the APU selector in the ON
position, the left forward fuel pump operates automatically.
If AC power is not available or no AC pump pressurizes the left fuel manifold, the
DC pump in the left main tank provides APU fuel. On the ground, the APU can
be started with no pumps operating.
When the APU air inlet door reaches the full open position the starter engages
(TBV). After the APU reaches the proper speed, ignition and fuel are provided.
When the APU reaches approximately 50 percent, the starter disengages and
ignition is turned off.
If the start fails, the APU shuts down automatically. The EICAS message APU
SHUTDOWN is displayed.
787 Flight Crew Operations Manual
Engines, APU -
APU System Description
7.30.2 Boeing Proprietary
APU Automatic Start
In flight, if both AC transfer busses lose power, the APU automatically starts,
regardless of APU selector position. When the automatic start condition is no
longer true, the APU can be shut down by positioning the selector to ON, then
OFF. When the automatic start condition is true, the APU only can be shut down
by pulling the APU fire switch.
APU Run
The EICAS memo message APU RUNNING is displayed when the APU is
operating normally.
APU Shutdown
Rotating the APU selector to OFF begins the shutdown cycle. The APU continues
running for a cooldown period. The EICAS memo message APU COOLDOWN
is displayed during the cooldown period. When the cooldown period finishes, the
APU shuts down.
APU Operating Modes
The APU has attended and unattended operating modes. The attended mode
operates when either engine is running or starting, or when the airplane is in flight.
The unattended mode operates at all other times 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 starting failure
• 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 message
APU LIMIT displays:
• high EGT
• high oil temperature
• low oil pressure.
There is no cooldown period when the APU is shut down after the APU LIMIT
message is displayed.
787 Flight Crew Operations Manual
Engines, APU -
APU System Description
Boeing Proprietary 7.30.3
APU Unattended Mode
In the unattended mode, any of the following faults cause the APU to shutdown
　
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