APU Flashcards

0
Q

What will cause an immediate APU shutdown in attended mode?

A
  • Inlet door failed closed
  • APU Controller fault
  • Start failure
  • Overspeed or loss of Overspeed protection
  • Speed droop
  • APU fire or inlet overtemperature
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1
Q

When is the APU is Attended Mode?

A

With either engine running or in flight.

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2
Q

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

A

Only the right starter.

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3
Q

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

A

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

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4
Q

Are both batteries required for APU start?

A

Both batteries required.

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5
Q

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

A

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

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6
Q

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

A

EICAS “APU SHUTDOWN” advisory

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7
Q

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

A

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

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8
Q

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

A

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

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9
Q

What is the operating ceiling limit for the APU?

A

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

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10
Q

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

A

14.000’

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11
Q

When does the APU automatically start?

A

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

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12
Q

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

A

By pulling the APU fire switch.

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13
Q

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

A
  • 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
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14
Q

Is there a cooldown period for automatic APU shutdowns?

A

No

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15
Q

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

A

EICAS “APU LIMIT”

  • High EGT
  • High oil temperature
  • Low oil pressure
16
Q

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

A

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

17
Q

What indication is given when the APU is running?

A

EICAS memo “APU RUNNING”

18
Q

When does the APU cool down timing begin?

A

When the APU selector is set to OFF.

19
Q

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

A

2 minutes

EICAS “APU COOLDOWN”

20
Q

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

A

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

21
Q

What APU functions are powered by the APU battery?

A

APU battery powers APU controller, air inlet door, and right starter.

22
Q

Which APU functions are powered by the main battery?

A

Main battery powers APU fuel shutoff valve, DC fuel pump and fire detection system.