APU

Question 1

Max altitude for APU starting?

Answer 1

37,000 ft

Question 2

What will happen if APU air is selected on immediately after APU start?

Answer 2

The APU air will turn on 90 second later

Question 3

Will the APU start if the READY light is not illuminated?

Answer 3

If the ECU BIT test did not pass, APU start in not inhibited with the absence of READY light. If the crew deems that time is critical, the option of proceeding with APU start is still available. APU air inlet door must be verified open prior to attempting start.

Question 4

What altitude is the 36-150 APU designed to operate and produce electrical power?

Answer 4

37,000 ft

Question 5

Normal shutdown of the APU is accomplished by pushing what switch?

Answer 5

APU stop switch

Question 6

Selecting what switch to the OFF position will close the APU fuel shutoff valve immediately?

Answer 6

APU master switch

Question 7

Prior to starting the APU, how can the position of the right engine lower cowl door be checked?

Answer 7

Visually or by using the 2/3rd “Doors” Synoptic page

Question 8

If necessary, how can the batteries be warmed most effectively prior to APU start?

Answer 8

Use an external AC power cart to charge and warm the batteries

Question 9

What is the minimum acceptable battery voltage prior to an APU start?

Answer 9

22V

Question 10

When is the APU air load control valve automatically inhibited OFF?

Answer 10

During APU start, and after APU start for 90 seconds

Question 11

How is it determined that all parameters are acceptable for APU start?

Answer 11

The APU “READY” light will be illuminated

Question 12

After APU start, when will the APU generator automatically power the electrical buses?

Answer 12

Four seconds after the APU achieves 95% RPM (assuming that the APU GEN switch is already in the normal ON position)

Question 13

How is an APU start manually aborted, such as during a hung start?

Answer 13

Depress the APU STOP switch, which triggers the 108% overspeed circuit, resulting in an immediate start abort

Question 14

How long are the APU RPM and EGT indications displayed after shutting down the APU?

Answer 14

For 5 minutes after the APU RPM is less than 5% and the APU MASTER switch is selected OFF (provided the APU ECU has a source of power)

Question 15

What are the limitations for starting the APU with an external DC power cart?

Answer 15

Wait 15 minutes between start attempts

Question 16

Would an APU FIRE cause the APU to shutdown in-flight or on the ground?

Answer 16

Both on the ground and in-flight

Question 17

Describe a normal APU shutdown.

Answer 17

Once the STOP switch is pressed, the ECU shuts down the APU by generating and overspeed signal to shut off fuel to the APU. The air inlet door is fully closed only after the APU rpm degrades below 35%.

Question 18

At what point will the APU ECU close the inlet door when the MASTER switch is used to shut down the APU?

Answer 18

It will close immediately

Question 19

Is the APU ECU still powered after the APU master switch is deselected?

Answer 19

Yes, for 5 minutes

Question 20

What is the rating of the APU generator, and is it interchangeable with the main generators?

Answer 20

40 kVA, it is not interchangeable with the engine IDGs

Question 21

Can the APU provide pressurization in flight?

Answer 21

No

Question 22

If an APU start attempt on battery power fails, how long a wait is required in order to try a second attempt?

Answer 22

Waiting is required after it fails a third attempt, then a 1 hour wait is required

Question 23

If an APU start attempt on external DC power fails, how long a wait is required in order to try a second attempt?

Answer 23

15 minutes

Question 24

If the APU was started on the ground, what mode will it be in flight?

Answer 24

Essential mode

Question 25

The APU will be in what mode if the master switch is placed ON in flight, but it is not actually started until on the ground?

Answer 25

Essential mode

Question 26

If landing with the APU running, how long will it stay in the essential mode?

Answer 26

15 minutes

Question 27

Where does the APU receive its fuel?

Answer 27

From the left boost pumps and tank. If it is necessary to use the right tank, the crossflow can be opened and right boost pressure used.

Question 28

What is the APU generator load limit when operating during flight?

Answer 28

The APU generator can deliver 100% electrical power (40 kVA) on the ground or in flight from sea level to 37,000 ft.

APU generator loading will be limited to 85% between 30,000 - 37,000 ft at speeds greater than Mach .85