Boeing 777 Auxiliary Power Unit (APU) – Startup and Components

Fill-in-the-blank flashcards reviewing key details of the Boeing 777 APU start sequence, components, and operation.

The Boeing 777 APU is a small gas-turbine engine located in the __.

tail cone

The APU supplies __ and pneumatic power to operate the aircraft independently on the ground.

electric

Besides ground operations, the APU provides backup power during __ emergencies.

flight

With no engines running and no external power, the only available power sources are the two aircraft __.

batteries

Selecting the main battery switch closes the contactors and energises the DC __ bus.

battery

Moving the APU switch to ON commands the APU fuel feed valve to __.

open

Because aircraft pneumatic power is unavailable during startup, the controller selects an __ start.

electric

The APU electric start system is powered by a dedicated __.

battery

The electric starter drives a ratchet wheel that turns the accessory gearbox via a __ clutch.

pawl

Mounted on the engine shaft are two-stage __ compressors.

centrifugal

In a compressor stage, the impeller accelerates the airflow, while the __ increases its pressure.

diffuser

At 7 % engine RPM, the controller opens the fuel __ valve.

shut-off

The ignition system is energised at 7 % RPM using a __-volt DC supply.

28

The APU combustion chamber is a reverse-flow __ chamber.

annular

Peak temperature inside the combustor can reach approximately __ °C.

2000

The turbine section of the APU consists of a three-stage __-flow turbine.

axial

To prevent flame-out, the ignition system remains active until the engine reaches __ % RPM.

50

At around __ % RPM, the APU’s electric and pneumatic power become available.

100