APU

Question 1

What is the primary purpose of the APU

Answer 1

The primary purpose of the APU is to provide electrical power

Question 2

Name some things that would cause the APU to automatically shutdown on the ground or in flight

Answer 2

Overspeed
Loss of overspeed protection
Loss of speed sensor signals
No APU rotation
No APU lightoff
Slow start
No acceleration
Speed fallback
APU fire/emergency
Loss of air inlet
APU door failure
Uncommanded door closure
ECU internal failure
Loss of DC power

Question 3

Will the APU shutdown on the ground due to high oil temp or low oil pressure?

Answer 3

Yes

Question 4

Will the APU shutdown in flight due to high oil temp or low oil pressure?

Answer 4

No

Question 5

If the APU shuts down automatically due to fire on the ground will the bottles fire?

Answer 5

Yes

Question 6

If the APU shuts down automatically due to fire in flight will the bottles fire?

Answer 6

No

Question 7

At what altitude will the surge control valve open?

Answer 7

17, 000

Question 8

What is the maximum altitude for APU operation

Answer 8

FL410

Question 9

What is the maximum altitude for APU start?

Answer 9

FL 370

Question 10

What is the maximum altitude for APU bleed air extraction?

Answer 10

FL250

Question 11

The APU will not start if the APU rpm is rotating above what speed on the ground verses in flight?

Answer 11

5% on the ground

12% in flight

Question 12

If the APU door is open or the door position is unknown with the APU shutdown, what is the limitation?

Answer 12

Flight is restricted to 220 Kts

Question 13

What is the primary reason for the previous (220 kts) Restriction?

Answer 13

To prevent the APU from wind-milling without the proper lubrication, and to ensure the APU rpm remains below 12% in the event it becomes necessary to start the APU in flight

Question 14

Is there a way around the 220 Kts restriction with the APU door open?

Answer 14

Yes, turn on the APU

Question 15

What provides fuel to the APU?

Answer 15

28 VDC pump feeding from the left collector tank

Question 16

If the APU fuel pump fails will the APU continue to operate

Answer 16

Yes, but it cannot be restarted without the pump

Question 17

What is the purpose of the Load Control Valve (LCV)

Answer 17

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

Question 18

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

Answer 18

No

Question 19

What is the minimum battery voltage for APU start?

Answer 19

22 volts

Question 20

What are the APU starter limitations?

Answer 20

Maximum of 3 starts per hour with a 2 minute cooling period in between

Question 21

What powers the APU door, and what powers the ECU?

Answer 21

The APU battery powers the door and is secondary for the ECU

The Main battery is the primary power source for the ECU

Question 22

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

Answer 22

Yes, through the use of an APU shutoff switch on the forward nose, or in the APU compartment