APU Flashcards

1
Q

Up to what altitude is electric power available?

A

41,000 feet.

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2
Q

Up to what altitude are both bleed and electric power available?

A

23,000 feet.

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3
Q

What is the maximum altitude for a battery start and for an AC network start?

A

-Battery start: 25,000 feet
-AC network start: 41,000 feet

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4
Q

How many stages does the APU turbine have?

A

3 stages.

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5
Q

What prevents coking in the fuel nozzles during APU shutdown?

A

The compressor forces air out the fuel nozzles.

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6
Q

What operates the inlet guide vanes of the APU?

A

Fuel muscle.

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7
Q

How many shafts does the APU have?

A

One (Single shaft)

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8
Q

What type of compressor does the APU power section have?

A

A 2-stage centrifugal compressor

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9
Q

How many fuel nozzles does the APU have?

A

12 fuel nozzles

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10
Q

How many fuel manifolds are in the APU, and what are they called?

A

Two: Primary and Secondary

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11
Q

Which APU fuel manifold is used during start?

A

The Primary manifold

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12
Q

When do both APU fuel manifolds supply fuel?

A

At high speed (High N speed)

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13
Q

What causes the secondary fuel manifold to begin supplying fuel?

A

Fuel pressure builds up and eventually overcomes the restrictors

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14
Q

What components are driven off the APU accessory gearbox?

A

Starter, AC generator, lubrication unit, fuel control unit

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15
Q

What does the ECB (Electronic Control Box) control?

A

Bleed valve, surge control valve, ignition unit, inlet guide vanes, inlet flap control

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16
Q

Which valve does the ECB use to prevent compressor surge?

A

The surge control valve

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17
Q

Which component controls the APU bleed valve?

A

The ECB (Electronic Control Box)

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18
Q

What is the function of the surge valve in the APU, and where does it dump surges?

A

The fuel muscle operated surge valve is constantly modulating and will dump surges into the APU exhaust.

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19
Q

How many EGT sensors (rakes) are installed in the APU exhaust?

A

There are 4 EGT sensors (rakes) installed in the exhaust.

20
Q

What component in the APU monitors for overspeed, and where is it installed?

A

An overspeed sensor is installed in the gearbox.

21
Q

How many hook latches and pin latches hold the APU doors together?

A

There are 3 hook latches holding the APU doors together, with a pin latch on either end of each door.

22
Q

How many hours of APU operation does the oil level allow when the “OIL LEVEL: CHECK” message appears?

A

The oil level allows for 60 hours of APU operation when this message appears.

23
Q

Where is the manual operation for the APU inlet flap available?

A

The manual operation for the inlet flap is available via the aft THS compartment.

24
Q

How many switches control the position of the air intake flap actuator?

A

There are 2 limit switches and 2 position switches controlling the air intake flap actuator.

25
Q

How can you bleed the APU fuel system?

A

Bleeding the APU fuel system is done from the APU compartment by pressing the push button, then opening the valve and bleeding the system.

26
Q

What component assists in cooling the APU compartment and oil cooler?

A

A fan assists in drawing air into the APU compartment for cooling and also provides cooling air for the oil cooler.

27
Q

How many mounts and tie rods secure the APU, and what is installed on the tie rods?

A

The APU is secured by 3 mounts and 7 tie rods, which have vibration isolators installed.

28
Q

Where are the APU drains located, and what do they drain?

A

There are 2 drains aft of the APU door, one for engine drain and one for accessory drain (fuel, oil, water, etc.).

29
Q

What module stores APU data, starts, shutdowns, and hours?

A

The Data Memory Module (DMM) stores APU data, including starts, shutdowns, and operational hours.

30
Q

What is the position of the Inlet Guide Vanes (IGV) during APU start and engine start?

A

The IGV is closed during APU start to unload the shaft and fully open during engine start.

31
Q

What are the three non-inhibited shutdown conditions for the APU?

A

1- Overspeed
2- ECB internal failure
3- Emergency

32
Q

Where are the low oil quantity switch and electrical chip detector located?

A

At the bottom of the oil tank, which is also the bottom of the gearbox.

33
Q

What additional components (temp related) are installed in the APU oil tank?

A

A low oil temperature sensor and an oil heater.

34
Q

At what speed does the green EWD memo “APU Avail” appear, and when does the green “Avail” light on the start button illuminate?

35
Q

From where is the APU bleed air taken?

A

From the single-stage load compressor.

36
Q

What is the standard oil pressure at 100% N?

A

About 65 degrees.

37
Q

What indicates that the starter motor needs to be replaced?

A

If the green brush wear indicator is no longer visible.

38
Q

At what speed does ignition turn on and off?

A

On at 7% N, off at 50% N.

39
Q

At what speed does the de-oiling valve close if it was open?

40
Q

At what speed does the fuel metering valve open?

41
Q

How many supply and scavenge pumps does the APU lube unit have?

A

3 supply pumps and 4 scavenge pumps.

42
Q

What does the de-oiling solenoid valve do?

A

It allows air into the inlet side of the pressure pump during specific start conditions (cold temp) and APU shutdown.

43
Q

What happens if the oil temperature is low on start?

A

Oil bypasses the oil cooler via a thermal valve.

44
Q

Where does the air-oil separator vent air?

A

Into the exhaust.

45
Q

What will cause an auto shutdown on the ground but requires crew action in-flight?

A

A Low oil pressure indication or high oil temp indication.

46
Q

When does the oil heater automatically turn on?

A

When the aircraft is powered up, the APU master switch is off, and oil temperature is less than 21°C.