APU

Question 1

What RPM range will the APU starter cutout?

Answer 1

Gnd: 46%
Flight: 46 - 60%

Question 2

What are the APU starter limits?

Answer 2

3 attempts in 1 hour with 2 minutes cool down between each start attempt.

Question 3

What will the APU automatic fire protection provide in flight?

Answer 3

Automatic shutdown of the APU, no automatic discharge of the bottle

Question 4

Where does the fuel to operate the APU come from?

Answer 4

From the Lt Collector tank, via a dedicated 28V DC pump

Question 5

Prior to APU start, what should the minimum battery voltage be?

Answer 5

22V on both the APU BATT DIR BUS and

MAIN BATT DIR BUS

Question 6

The APU ECU will inhibit start if the APU rotates above ___% in flight and ____% on the ground.

Answer 6

12% in flight

5% on the groundand

Question 7

Max altitude for APU start?

Answer 7

37,000 ft

Question 8

Max altitude for APU operation?

Answer 8

41,000 ft

Question 9

Max altitude for Bleed Air extraction?

Answer 9

25,000 ft

Question 10

Can the APU be used as a source of bleed air for ice protection?

Answer 10

No

Question 11

If the APU door is stuck open or it’s position is unknown, what must be done?

Answer 11

• Max airspeed of 220 knts OR

- run the APU continuously with no speed restriction.

Question 12

Describe the APU door

Answer 12

Ground: Door id closed at 0 degrees when OFF and
45 degrees when running
Flight: Door modulates between 0 and 45 degrees

Question 13

What is the APU’s main priority?

Answer 13

Electrical power: 115 VAC, 400Hz, 40 KvA

Question 14

APU Bleed air is controlled by modulating what?

Answer 14

APU LCV (Load control valve)

Question 15

If the APU electrical fuel pump FAILS while the APU is running, will the APU continue to run?

Answer 15

Yes. But the APU will not start once it is shut down.

Question 16

Will the APU shutdown on the ground due to High oil Temp or Low oil pressure?

Answer 16

Yes

Question 17

Will the APU shutdown in flight due to High oil Temp or Low oil pressure?

Answer 17

No

Question 18

Will the APU automatically shutdown on the ground due to fire, and will the bottle automatically fire?

Answer 18

Yes

Yes

Question 19

Will the APU automatically shutdown in flight and will the bottle automatically fire?

Answer 19

Yes

No

Question 20

At what altitude will the surge valve open?

Answer 20

17000’

Question 21

Name 14 things that would cause the APU to automatically shutdown.

Answer 21

• APU Fire
• APU Door failure
• ECU Internal failure
• Loss of DC Power
• Loss of air inlet
• Loss of over speed protection
• Loss of speed sensor signals
• No APU Acceleration
• No APU Rotation
• No APU Light-off
• Overspeed > 106%
• Slow start
• Speed fallback
• Uncommanded door closure

Question 22

What is the purpose of the Load control valve? (LCV)

Answer 22

The LCV varies pneumatic load to ensure electrical power and 45 psi in the manifold

Question 23

Can APU bleed air be used by the anti-ice system?

Answer 23

No

Question 24

What powers the APU door?

What powers the ECU?

Answer 24

The APU Battery provides power to the APU door and is secondary for the ECU
The MAIN Battery is the primary power source for the ECU

Question 25

If the APU is left unattended, can the ground crew shut it down? Where?

Answer 25

Yes. APU shutoff switch on the forward service panel, or in the AFT equipment bay