APU

Question 1

What will cause an immediate APU shutdown in attended mode?

Answer 1

• Inlet door failed closed
• APU Controller fault
• Start failure
• Overspeed or loss of Overspeed protection
• Speed droop
• APU fire or inlet overtemperature

Question 2

During an APU start on battery power, which starter(s) are used?

Answer 2

Only the right starter.

Question 3

How many APU start attempts are made by the system on APU battery power?

Answer 3

Two consecutive start attempts, then a 5 minute cool down.

Question 4

Are both batteries required for APU start?

What is powered by the APU/main battery?

Answer 4

Both batteries required.
APU battery powers APU controller, air inlet door, and right starter.
Main battery powers APU fuel shutoff valve, DC fuel pump and fire detection system.

Question 5

When starting APU from an unpowered airplane, what must the APU controller wait for before proceeding with APU start?

Answer 5

APUC waits until CCS applications are available before proceeding with the start. Fire detection and fuel management applications are necessary.

Question 6

If an APU start fails, will an EICAS message display?

Answer 6

EICAS “APU SHUTDOWN” advisory

Question 7

If AC power is not available for APU start, what is the source of APU fuel?

Answer 7

Dedicated DC fuel pump in the left tank, powered by the main battery.

Question 8

Once AC power is available, which pump supplies fuel pressure to the APU?

Answer 8

Fuel supplied by the left manifold by any AC pump. Left AFT AC pump commanded on with AC power available and APU switch on.

Question 9

What is the operating ceiling limit for the APU?

Answer 9

APU can be started and operated to the airplane maximum certified altitude.

Question 10

What is the max altitude the APU can be started with no fuel pumps operating?

Answer 10

14.000’

Question 11

When does the APU automatically start?

Answer 11

In flight, when three or more engine generators go offline.

Question 12

When APU automatic start condition is valid, what is the only way of shutting down the APU?

Answer 12

By pulling the APU fire switch.

Question 13

What faults will cause the APU to shut down in the unattended mode?

Answer 13

• Inlet door failed closed
• APU Controller fault
• Start failure
• Overspeed or loss of Overspeed protection
• Speed droop
• APU fire or inlet overtemperature
• High EGT / loss off signal
• High oil temperature
• Low oil pressure
• ASG oil filter approaching bypass

Question 14

Is there a cooldown period for automatic APU shutdowns?

Answer 14

No

Question 15

For which faults will the APU continue to run with EICAS caution message?

Answer 15

EICAS “APU LIMIT”

• High EGT
• High oil temperature
• Low oil pressure

Question 16

In flight with an APU fire, will the APU fire bottle automatically discharge?

Answer 16

Yes, in flight or on the ground with a 15sec delay.

Question 17

What indication is given when the APU is running?

Answer 17

EICAS memo “APU RUNNING”

Question 18

When does the APU cool down timing begin?

Answer 18

When the APU selector is set to OFF.

Question 19

How long is the APU cool down time and is there any indication?

Answer 19

2 minutes

EICAS “APU COOLDOWN”

Question 20

What happens at the end of the cooldown time to accomplish a final shutdown?

Answer 20

An APU Overspeed is simulated to test the Overspeed and fuel shutoff protection.

Question 21

When is the APU is Attended Mode?

Answer 21

With either engine running or in flight.