APU

Question 1

How is the APU intake flap opened? What happens if you press the START pb prior to flap opening?

Answer 1

APU master switch ON.

The APU computer (ECB- Electric control box) will not permit APU to start until flap is fully open.

Question 2

What is the normal function of APU MASTER SW pb?

Answer 2

Controls electric power supply to APU and turns on the ECB.

Question 3

Will APU shutdown with a LOW OIL LEVEL message?

Answer 3

No. APU may be started and operated, however maintenance is required within the next 10 hours of APU operation.

Question 4

Will APU shutdown due to low oil pressure?

Answer 4

Yes. No message displayed, and ECB directs APU to automatically shutdown.

Question 5

Where is APU fuel supplied from?

Answer 5

APU fuel supply line is directly connected to engine 1 feed line- normally supplied by left inner tank.

Question 6

When does the APU DC fuel pump operate?

Answer 6

If there is no fuel pressure in engine 1 feed line when APL MASTER SW pb selected ON, ECB energises it. No flight deck indications.
*when engine 1 fuel line pressurises, ECB shuts down APU fuel pump.

Question 7

What happens if FUEL LO PR appears on APU page?

Answer 7

APU automatically shuts down.

Question 8

At what N% will ON light extinguish on APU START pb and AVAIL appear on pb and APU page?

Answer 8

95% N

Question 9

On shutdown will the APU need to cool?

Answer 9

If bleed air was in use, APU will run for a cooling period of 60-120 seconds at 75%N.

Question 10

When will APU automatically shutdown due to EGT?

Answer 10

EGT reaches redline. Amber line indicates 33 deg below max.

Question 11

Will APU automatically shutdown if an APU fire is detected?

Answer 11

Inflight- No- flight crew must manually shutdown.
On ground- Yes- ECB will command an automatic shutdown and halon extinguisher automatically discharged.

Question 12

What is the service ceiling of APU? What is the maximum altitude for start?

Answer 12

Ceiling- 39000ft.
Start- 25000ft.

Question 13

What altitude is APU bleed air available up to?

Answer 13

22500ft.

Question 14

What is the maximum pressure altitude for an APU ground start/operation?

Answer 14

14500ft.

Question 15

What is the APU max N speed?

Answer 15

107 % N.

Question 16

What is the APU starting and operating max EGT?

Answer 16

Starting- 1090
Operating- 675

Question 17

What is the APU starter motor duty cycle?

Answer 17

3 attempts with 1 minute cooling, then 60 minute cooling.

Question 18

How can cold soaking of APU compartment affect starting?

Answer 18

A start cannot be guaranteed if aircraft has been airborne above 8000ft for longer than 1.5hours.

Question 19

Should APU start be attempted in emergency electrical configuration?

Answer 19

If fuel remains, the flight crew should attempt an APU start regardless of the RAT type in order to recover cabin pressurization, additional electrical power and have bleed available for a starter-assisted relight, if necessary.

Each APU start attempt reduces flight time on batteries by about 3 and a half minutes. Total flight time on batteries is more than 30 min.

PR-AEP-ENG P 2/26