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M15✅ > 15.8 APU👌🏼 > Flashcards

15.8 APU👌🏼 Flashcards

1
Q

Explain APU

A
  • small gas turbine
  • supplies pneumatic + electrical power
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2
Q

What is the primary requirement to achieve ETOPS certification

A
  • aircraft possession of an in-flight APU
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3
Q

APU require low starting altitude which is around

A
  • 15000ft-17000ft
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4
Q

APUs are capable to operate up to what altitude

A

40000ft

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5
Q

APU is split into 3 main sections

A
  • power section
  • bleed section
  • accessory gearbox section
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6
Q

What accessories are driven by the gearbox

A
  • fuel pump
  • oil pump
  • cooling fan
  • ac generator
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7
Q

2 ways APU air can be bled

A
  • APU compressor
  • load compressor
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8
Q

What does the power section on gas turbines contain

A
  • compressor
  • combustion chamber
  • turbine
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9
Q

Why are In flight APU often started during landing phase

A

To ensure in case of go-around there is maximum engine power available

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10
Q

What are the combustion chambers type for modern APU

A

Annular type

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11
Q

What fire protection system is on the APU

A
  • fire extinguisher that activates automatically
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12
Q

The AC generator is at a constant speed supplied by what

A

APU

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13
Q

Electronic APU control unit has 3 separate operating modules which are

A
  • start mode
  • normal speed
  • APU shut down
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14
Q

Explain start mode control

A

APU from start to 100% speed

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15
Q

Explain normal speed mode

A

Remain at 100% speed regardless of load changes

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16
Q

Explain APU shut down mode

A
  • monitors and controls APU shut down
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17
Q

2 reasons APU control unit is monitored

A
  • optimise APU start sequence
  • protect APU from damage
18
Q

What are the 2 signals for constant speed control

A
  • APU speed signal
  • torque motor signal
19
Q

APU fuel is taken from where

A
  • aircraft’s main engine fuel feed system
20
Q

APU cool down period varies between

A

0-120 seconds (can be adjusted)

21
Q

When is the APU allowed to shutdown

A

After operating for a sufficient time without pneumatic or electric load

22
Q

How can the APU be kept at 100% speed with high bleed loads?

A

Add more fuel (results in higher EGT)

23
Q

If APU has load compressor what system does it belong to

A

Air bleed system

24
Q

2 conditions must be met to open the APU bleed valve

A
  • APU bleed switch ON
  • APU start sequence must be complete
25
Q

When APU is shut down why is there a time delay

A
  • So APU can run with no loads to cool down
26
Q

Advantage of load compressor control

A
  • more fuel efficient
27
Q

Can the load compressor be switched off

A

No as it is fixed to the rotor shaft

28
Q

What does the surge protection system prevent

A
  • any surge condition of the APU compressors
29
Q

When can APU compressors surge

A

When bleed load changes

30
Q

Automatic APU shutdown is activated by what

A

APU control unit

31
Q

APU start sequence ends when APU speed becomes greater than what percentage

A

95%

32
Q

Where are the APU external emergency shut-down switches located

A
  • NL gear
  • main wheel well
  • on refuelling station
33
Q

Is the automatic APU emergency shutdown activated in a fire condition when aircraft is on ground

A

Yes

34
Q

Explain anti-surge valve

A

Operated during flight to prevent surging

35
Q

Air inlet into the load compressor is closed off by ?

A

Inlet guide vanes

36
Q

Surge protection system is used on what

A

APU’s with Load compressor

37
Q

Explain how the surge protection method works

A

-monitors airflow
- opens a surge control valve if compressor surges

38
Q

Does automatic shutdown have a cooling period

A

No it is immediately shut

39
Q

When pressing FIRE button what occurs to APU

A

Immediately shut down

40
Q

When a FIRE occurs at APU what occurs

A

Immediately shut down

M15✅ (16 decks)

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