APU

Question 1

What services does the APU provide and what are they used for?

Answer 1

An electrical generator supplies 28 V DC to the electrical system. The pneumatic power is used for engine
starting and to supply bleed air to the air-conditioning pack of the environmental system (ECS). AOM 9-04-01

Question 2

How is the APU controlled and monitored?

Answer 2

Through a dedicated Full Authority Digital Electronic Control unit (FADEC). AOM 9-04-01

Question 3

What does pressing the APU ON/OFF button do?

Answer 3

It starts the ECU power-up sequence and initiates the APU built-in test (BIT). AOM 9-04-30

Question 4

When does the START button on the APU CONTROL panel flash green?

Answer 4

During the ECU bit test. AOM 9-04-30

Question 5

What does the START button on the APU control panel illuminating steady green indicate?

Answer 5

The APU is ready to start. AOM 9-04-30

Question 6

If the START button on the APU control panel illuminates amber what does that indicate?

Answer 6

The APU start is inhibited. AOM 9-04-30

Question 7

What are the APU starter limitations?

Answer 7

Up to three consecutive unsuccessful start attempts are allowed with 30 second intervals between
attempts. AOM 2-38

Question 8

What MFD page can APU information be seen on?

Answer 8

The STATUS synoptic page. AOM 9-04-30

Question 9

Which tank normally supplies fuel to the APU?

Answer 9

The right tank. AOM 9-04-50

Question 10

Is it possible to feed the APU from the left wing tank? If so, how?

Answer 10

Yes, via the cross-feed system. AOM 9-04-50

Question 11

Can the APU supply bleed air on the ground or in flight?

Answer 11

Yes. AOM 9-04-50

Question 12

If the APU is the only source of electrical power on the ground, what buses can the APU power?

Answer 12

All of the airplane electrical loads and charge both batteries. AOM 9-04-30

Question 13

If the APU is the only source of electrical power in flight, what buses can the APU power?

Answer 13

All electrical loads (except for the SHED BUSES) and also charging both batteries. AOM 9-04-50

Question 14

What is the APU operating envelope for starting, operation and to supply electrical power?

Answer 14

Up to 31,000 feet. AOM 9-04-50 and AOM 2-38

Question 15

Up to what altitude is the APU able to supply bleed air for engine starting?

Answer 15

Up to 23,000 feet. AOM 9-04-50 and AOM 2-38

Question 16

Where does the APU get its power for starting?

Answer 16

The number two battery. AOM 9-04-50

Question 17

What should be displayed on the STATUS synoptic page if the APU oil quantity is sufficient?

Answer 17

A green “OK” AOM 3-01-10

Question 18

List the 4 conditions that will cause the APU to automatically shut down either in flight or on the ground.

Answer 18

Overspeed, under speed, ECU internal failure or an APU bleed leak. AOM 9-04-50

Question 19

List the conditions that will cause the APU to automatically shut down on the ground only.

Answer 19

APU fire, APU EGT over temperature, APU high oil temperature, APU low oil pressure, APU starter not
engaged or an APU fuel shut off valve failure. AOM 9-04-50