APU

Question 1

The Auxiliary Power Unit (APU) is a gas turbine engine located in the airplane tailcone, which provides pneumatic and electrical AC power. The pneumatic power is used for engine starting and to supply bleed air to the air conditioning packs of the Environmental Control System (ECS)

Answer 1

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Question 2

The APU is automatically monitored and controlled through a dedicated Full Authority Digital Electronic Control (FADEC) unit

Answer 2

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Question 3

APU EMERGENCY STOP BUTTON (GUARDED)

PUSH IN: closes the APU fuel shutoff valve, shutting down the APU with no cooldown period. A white striped bar illuminates on the lower half of the button.

PUSH OUT: normal position, with the fuel shutoff valve open.

NOTE When an APU fire is detected, the upper half of the button illuminates red

Answer 3

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Question 4

APU FUEL SUPPLY

A. When only DC power is available, the DC fuel pump, located in the right wing tank, provides fuel to the APU. If AC power is available and the engine is not running, fuel will be provided by the AC fuel pump.

B. When the engine is running, the ejector fuel pump provides fuel to the APU from the right wing tank. However, it is also possible to provide fuel to the APU from the left wing tank via a crossfeed valve.

Answer 4

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Question 5

The APU is able to supply:
(1) Electrical AC power up to 33000 ft.
(2) Bleed air for engine starting up to 21000 ft.
(3) Bleed air for air conditioning and pressurization up to 15000 ft.
E. Maximum altitude for APU start is 30000 ft

Answer 5

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Question 6

Three seconds after APU speed has reached 95%, electrical and pneumatic loading are available. If the APU does not reach proper speed or acceleration rate within the starting cycle time, the APU will
automatically shut down.

Answer 6

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Question 7

The battery #2 energizes the electronic starter controller.

Answer 7

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Question 8

During a normal shutdown sequence, the APU pneumatic power is removed immediately and the electrical power is removed at the end of a 2 minutes cooldown period.

The cooldown period is 1 minute, followed by a spooldown period.

Answer 8

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Question 9

In the event the APU emergency stop button has been selected, the APU fuel shutoff valve closes and the APU shuts down without a two-minute cooldown period.

Answer 9

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Question 10

The FADEC provides automatic APU shutdown protection on ground and in flight as follows.

Answer 10

On the ground

Overspeed
Underspeed
FADEC critical fault
fire 
overtemperature 
high oil temperature -
low oil pressure -
Sensor fail 

In flight

Overspeed
Underspeed
FADEC critical fault

Question 11

APU operates at a constant speed. consists of a single stage compressor impeller and a two stage axial turbine mounted on a common rotor shaft

Answer 11

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Question 12

When is electrical and pneumatics available from the APU after APU start?

Answer 12

95% plus 3 seconds

Question 13

What 3 things open or are energized when you move APU Start Knob to ON?

Answer 13

1. APU FADEC is energized
2. APU EICAS messages are displayed
3. APU Fuel SOV opens

Question 14

What is closed when the APU Emer. Stop Button is pressed?

Answer 14

1. Denergizes APU FADEC
2. Closed APU Fuel SOV
3. Overrides APU Master Switch