APU

Question 1

What is the primary purpose of the auxiliary power unit?

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 shut down on the ground or in flight.

Answer 2

Over speed greater than 106% loss of overspeed protection 
loss of speed sensor signal 
No APU rotation
No APU light off 
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 shut down on the ground due to high oil temp or low oil pressure?

Answer 3

Yes

Question 4

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

Answer 4

No

Question 5

If the APU shut down automatically due to fire on the ground will the bottle fire?

Answer 5

Yes

Question 6

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

Answer 6

No

Question 7

At what altitude will the surge control valve open?

Answer 7

17,000 feet

Question 8

What is the maximum altitude for APU operation?

Answer 8

Flight level 410

Question 9

What is the maximum altitude for APU start?

Answer 9

Flight level 370

Question 10

What is the maximum altitude for APU bleed air extraction?

Answer 10

FL 250

Question 11

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

Answer 11

5% on the ground and 12% in flight

Question 12

If the APU door is open or the door position is unknown with the APU shut down what is the limitation?

Answer 12

Flight is restricted to 220 knots

Question 13

What are the primary reasons for the speed re-striction?

Answer 13

To prevent the APU from windmilling 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 knot re-striction with the APU door open?

Answer 14

Yes. Normal speeds can be used if the APU is running

Question 15

What provides fuel to the APU?

Answer 15

A dedicated 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?

Answer 17

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

Question 18

Can 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 three start per an hour with a two minute cooling period In between

Question 21

What powers the APU door and what powers ECU?

Answer 21

The APU battery provides power to 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’t do ground crew shut it down?

Answer 22

Yes through the use of an APU shut off switch on the forward nose or in the APU compartment

Question 23

What is the absolute APU EGT?

Answer 23

1038’c or lesser value indicated on he EICAS display

Question 24

What is the maximum APU rpm?

Answer 24

106%