APU

Question 1

What is the primary function of the APU?

Answer 1

• Electrical power

- Pneumatic air for engine starts and air conditioning (Ground Only)

Question 2

What is the proper procedure for APU shutdown?

Answer 2

1. AUX PWR Switch OFF
2. Keep the APU Air in its current configuration
3. Press the APU Overspeed button
4. Turn the APU Air OFF below 95% RPM (if configured ON)
5. Turn off the APU master switch below 10% RPM (5% if 150 APU)

Question 3

What is the minimum acceptable APU or external air pressure required to start an aircraft engine?

Answer 3

25 psi

Question 4

What is the maximum acceptable AC AUX PWR load required for an engine start?

Answer 4

35 percent

30 percent at high elevation and/or high ambient temperatures

Question 5

What are the first four action items for an APU fire indication?

Answer 5

APU Over Speed Button – PRESS
APU Master Switch – OFF
APU Fire Extinguisher – DISCHARGE
APU Fire Test Switch - TEST

Question 6

What is the maximum altitude and airspeed for an APU start in flight?

Answer 6

15,000 feet

250 knots

Question 7

What is the APU guaranteed starting envelope?

Answer 7

15,000 feet and below

250 Kts max

Question 8

If the APU is shut down using the “OVERSPEED-TEST” button, what action must be accomplished before restarting the APU?

Answer 8

The APU master switch must be selected to OFF, and then to ON

Question 9

What is the APU electrical load limit?

Answer 9

Sea Level – 22,000’: 100%, 22,000 – 30,000’: 50%

High-Altitude APU:
Sea Level – 25,000’: 100%, 25,000 – 30,000’: linear decrease to 83%, 30,000 – 35,000’: 67%

ASC 465 (36-150[G] APU):
Sea Level to 15,000’ (20,000’ if below 300KIAS) – 100%
15,000’ – 30,000’ – 75%, 30,000’ – 35,000’ – 50%

Question 10

Does the APU produce AC or DC power?

Answer 10

• AC power production

- DC power is supplied through the TRU

Question 11

Does the APU have a converter?

Answer 11

• No

- APU always runs at 100% and produces stable 400 Hz power that does not require a converter.

Question 12

What conditions will cause automatic shut down of the APU? (5)

Answer 12

• APU fire
• high EGT
• high oil temperature
• low oil pressure
• over current in the ECU.

Question 13

Upon detection of a fire in the APU, will the fire extinquisher discharge automatically?

Answer 13

NO. The APU fire extinguisher must be manually discharged by lifting the guard and depressing the APU Fire Ext Switch.

Question 14

After an APU start, when will the APU Load Control Valve, allow the APU air for engine start and pack operation?

Answer 14

APU air is available after the APU RPM has reached an operating speed of 95% rpm for 4 seconds and EGT has stabilized for 2 minutes.

Question 15

From which Fuel Tank can the APU receive fuel?

Answer 15

• Fuel is drawn from the Left Wing Fuel Hopper using the Left Main and/or Left Alternate Fuel Pumps
• Fuel can be drawn through the Crossflow Valve using the Right Main and/or Right Alternate Fuel Pumps

Question 16

Max EGT APU running

Answer 16

732˚ C

Question 17

Max EGT with APU air on

Answer 17

680˚ C

Question 18

APU Operating RPM

Answer 18

100% ± 3%

Question 19

APU Over speed RPM

Answer 19

110%