APU System

Question 1

What is the APU used for?

Answer 1

Electrical and Bleed Air

Question 2

What monitors and controls the APU?

Answer 2

Its own dedicated FADEC.

Question 3

How are the batteries used for APU start?

Answer 3

• BATT 2 powers the APU START bus.

* BATT 1 powers the FADEC and EICAS for monitoring.

Question 4

What is the fuel source for the APU?

Answer 4

• Right fuel tank

* Left fuel tank through the crossfeed valve

Question 5

What fuel pump is used for APU start?

Answer 5

• Batteries ‘ON’ only DC… fuel pump
• AC powered aircraft… AC fuel pump 2
• Right engine running… Ejector fuel pump

Question 6

When does the APU electrical and pneumatic loading become available?

Answer 6

• APU icon is available on the ELEC synoptic page.

Question 7

Will the APU shutdown automatically if the APU fails to start within the normal start
cycle time period?

Answer 7

Yes.

Question 8

What does moving the APU selector knob to OFF do?

Answer 8

• Initiates normal APU shutdown.
• 1 minute cool down followed by a spooldown period.
• Pneumatics removed immediately and electrical power is removed after the 1 minute cool
down.

Question 9

Can the APU pneumatics be used during the cooldown period?

Answer 9

No.

Question 10

Can the APU electrical power be used during the cooldown period?

Answer 10

Yes.

Question 11

If you need the APU 50 seconds into shutdown is there a way to get its use back?

Answer 11

Yes, just turn the APU master switch back to ON.

Question 12

Can the APU shutdown be cancelled?

Answer 12

Yes, by moving the MASTER switch back to ON before the 1 minute cool down is over

Question 13

How can the APU be shutdown immediately?

Answer 13

• APU EMER STOP button

* No 1 minute cool down period.

Question 14

When will automatic shutdown of the APU occur?

Answer 14

• Ground: - All conditions
• Flight: - Overspeed
- Underspeed
- FADEC critical fault

Question 15

When will automatic shutdown of the APU occur?

Answer 15

• Ground:
- All conditions
• Flight:
- Overspeed
- Underspeed
- FADEC critical fault

Question 16

When do we get the red bar on the APU EMER STOP button?

Answer 16

• An APU fire is detected.

Question 17

What happens when the APU EMER STOP button is pushed?

Answer 17

The APU fuel shutoff valve closes and the APU will shut down with no cooling period. A
white stripe illuminates on the button.

Question 18

Does the cool down period apply to the APU EMER STOP button?

Answer 18

No.

Question 19

What is the maximum altitude for operation of the APU bleed?

Answer 19

15,000 feet

Question 20

What is the maximum altitude for APU operation?

Answer 20

33,000 feet

Question 21

What is the maximum altitude for APU start?

Answer 21

30,000 feet

Question 22

Up to what altitude may the APU assist in engine start?

Answer 22

21,000 feet

Question 23

In normal operations on the ground with the APU running, it would be normal to see the fuel unbalanced with less fuel in which tank?

Answer 23

Right tank