787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Engines, APU -
APU System Description
Copyright © The Boeing Company. See title page for details.
7.30.2 D615Z003-TBC
Either starter can be powered by forward external power or an engine generator.
The APU battery powers the APU controller (APUC), air inlet door, and the right
starter if required. The main airplane battery powers the APU fuel spar valve, DC
fuel pump, and fire detection system.
Rotating the APU selector to START begins the automatic start sequence.
Note: If starting the APU from an unpowered airplane (battery switch recently
moved to ON), the APUC waits until the common core system (CCS)
applications are available before proceeding with the start. The CCS fire
detection and fuel management applications are necessary to start the APU
and are available when the CDU page is visible on the lower display unit.
The APUC commands the air inlet door to open.
APU fuel is supplied from the left fuel manifold by any operating AC fuel pump,
or by the DC fuel pump in the left main tank. With AC power available and the
APU selector in the ON position, the left aft fuel pump is commanded on
regardless of flight deck switch position.
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. The DC pump continues to run
until either the APU is shut down or an AC pump supplies fuel pressure. The APU
is designed to be started with no pumps operating when on the ground or in-flight
up to 14,000 feet.
When the APU air inlet door reaches the full open position, and the required CCS
programs are running, the starter engages. Starter selection is automatic. On
battery power, only the right starter is used. After the APU reaches the proper
speed, APUC commands ignition and fuel. When the APU reaches starter cutout
speed (approximately 50% rpm), the starter disengages and ignition is turned off.
When the APU is running (95% of target speed + 2 seconds), the EICAS memo
message APU RUNNING is displayed and the APU is ready to power the
airplane.
If the start fails, the APU shuts down automatically. The EICAS advisory message
APU SHUTDOWN is displayed. Moving the APU selector from ON to OFF
clears the message and resets the shutdown system to enable a restart attempt.
The APU battery is designed to support two consecutive start attempts. If the APU
fails to start after the second attempt, a 5 minute cooling period must be observed
before a third attempt is made.
August 14, 2009
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