APU

Question 1

What are the start sources for the APU, and which one do we normally use?

Answer 1

APU Battery (DC electric starter)

Question 2

Can the APU be operated in flight?

Answer 2

When left running for takeoff can be operated up to 20,000’

Question 3

Is electrical power available from the APU in flight? How about APU bleed air in flight?

Answer 3

• Electrical Pwr: No

- Bleed air available for 1x PACK up to 15,000’

Question 4

What APU components are powered by the APU battery?

Answer 4

• L & R outflow valves
• IRU L/C/R DC Power
• APU inlet door
• APU Controller (Pri)

Question 5

What APU components are powered by the main battery?

Answer 5

• APU DC Fuel Pump
• APU Fuel SOV
• APU Fire Detection loops A & B

Question 6

What powers the APU starter during a battery start sequence?

Answer 6

APU Battery

Question 7

What happens if the TR should overheat with the start source in TR?

Answer 7

Starting power is transferred to the battery & start continues on battery power

Question 8

How does a TR failure affect APU starting?

Answer 8

Any further attempts to use TR inhibited

Question 9

When does the EICAS memo message APU RUNNING display?

Answer 9

• APU Selector “ON”

- APU N1 RPM > 95% N1

Question 10

Describe the APU shutdown sequence.

Answer 10

1- APU selector to “OFF” closes the APU bleed air valve
2- APU continues running unloaded for 60” cooldown
3- Shutdown

Question 11

What would happen if the battery switch is positioned OFF prior to completion of the APU shutdown cooldown period?

Answer 11

The APU will shutdown immediately

Question 12

How long should you wait before turning the battery switch OFF after the APU selector is rotated to OFF, and why?

Answer 12

2 minutes

To ensure complete shutdown sequence with fire detection capability.

Question 13

What would cause the APU to shut down automatically?

Answer 13

If a limit is exceeded or a fire detected