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CRJ 700 ENY STUDY GUIDE > APU > Flashcards

APU Flashcards

0
Q

What’s the APU’s secondary function?

A

The secondary function of the APU is to supply compressed air as a source of bleed air to power the environmental control system (ECS) and engine starting system.

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1
Q

What’s the APU’s primary function?

A

The primary function of the APU is to operate the gearbox mounted 40 KVA generator. To provide electrical power.

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2
Q

What is the maximum operating altitude of the APU?

A

41,000 feet

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3
Q

What is the maximum altitude to start the APU in flight?

A

37,000 feet

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4
Q

What is the maximum altitude for APU bleed air extraction?

A

25,000 feet

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5
Q

What is the function of the APU intake door?

A

To supply ambient (static or ram) air to the air inlet ducting for APU operation.

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6
Q

What positions the APU intake door during normal operations?

A

The APU intake door actuator positions the intake door based on input from the APU electronic control unit (ECU).

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7
Q

In what position is the APU intake door during ground start?

A

100% open for start and on speed condition for ground operations.

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8
Q

In what position is the APU intake door during inflight start?

A

In flight the APU intake door opens with the “START/STOP” switch light and its position will vary with the APU speed and aircraft Mach number.

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9
Q

Why does the APU intake door not open in flight until the “START/STOP” switchlight is pressed?

A

This prevents early exposure of the APU to excessive amounts of ram air, resulting in “blowout” and APU windmilling.

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10
Q

What is the maximum allowable airspeed if the APU instake door position is open or unkown while in flight?

A

Airspeed is restricted to 220 knots, or the APU must remain in operation.

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11
Q

Where is the APU intake door position indicated in the cockpit?

A

On the Status Page.

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12
Q

Which tank normally supplies the APU with fuel?

A

The left collector tank.

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13
Q

What two switchlights control the APU Fuel Shutoff Valve?

A
  • The APU PWR / FUEL switchlight
  • The APU FIRE PUSH switchlight
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14
Q

What is the function and location of the APU Fuel Shut-off Solenoid Valve?

A
  • It is located between the Fuel Control Unit and the spray nozzles
  • It modulates to increase or decrease the amount of fuel directed to the fuel nozzles
  • It closes (simulates an overspeed) to shut down the APU
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15
Q

What occurs when the “APU PWR FUEL” switchlight is selected?

A
  • Activates the APU Electronic Control Unit (ECU)
  • Activates the APU Fuel Pump
  • Opens the APU Fuel Shutoff Valve
  • Activates the APU EICAS Displays
  • Initiates a prestart IN BITE feature
  • Opens the APU Instake Door on the ground
16
Q

What component controls the operation and control of the auxillary power unit (APU) fuel system?

A

The APU ECU

17
Q

How is the APU cooled?

A
  • APU compartment cooling is accomplish by the exhaust eductor. On the ground, the venturi effect created by the APU exhaust causes air to be drawn from the air inlet, through the oil cooler and into the APU compartment. The air is then removed from the compartment by the eductor. In flight, the ram air from the air inlet is pushed into the compartment through the oil cooler and then removed by the eductor.
18
Q

What is the function of the APU Electronic Contrl Unit (ECU)?

A

The function of the ECU is to control all normal modes and emergency shutdown of APU operation.

19
Q

When does the APU starter disengage?

A

Between 46% and 60% rotor speed depending on altitude.

20
Q

What is the function of the “APU IN BITE” check?

A

The ECU does checks before the ignition/start sequence. Before the ignition/start sequence can begin, the ECU must satisfactorily complete the prestart built-in-test-equipment (BITE) check of all APU and ECU related components.

21
Q

What controls the APU ignition system?

A

The ECU using 28 volt DC power from the DC Battery Bus as its primary source (and the Main Battery Direct Bus as its secondary source) to energize the ignition system during the ignition/start sequence.

22
Q

What is the minimum battery voltage required to start the APU?

A

Both the Main and APU batteries are required to start and operate the APU. The minimum battery voltage for both batteries is 22 volts.

23
Q

What are the power sources for the APU ECU and Starter during an APU start?

A
  • ECU is powered by the Main Battery Bus
  • APU Starter is powered by the APU Battery Bus
24
Q

What is the APU overspeed limit?

A

106% rotor speed

25
Q

What is the function of the APU Load Control Valve (LCV)?

A

When the LCV is open, a portion of the compressed discharge air is diverted to the left side of the bleed manifold. This air can be used for environmental services or engine starting.

26
Q

What happens to the APU RPM and EGT when the LCV opens?

A
  • RPM drops and then recovers when the APU ECU commands a fuel flow increase
  • The EGT rises as a result of the increased fuel flow
27
Q

What will the ECU do to the LCV if the exhaust gas temperature limit is reached?

A

The ECU will reduce the bleed flow by modulating the LCV toward the closed position to prevent over temperature. This lowers the pneumatic load on the APU and maintains EGT within acceptable levels.

28
Q

What is the maximum APU exhaust gas temperature?

A

1,038 C

29
Q

When is bleed air available after APU start while on the ground?

A

99% rpm + 60 seconds.

30
Q

When is bleed air available after APU start while in flight?

A

99% rpm + 2 seconds.

31
Q

What is the function of the “START” illumination in the APU START/STOP switchlight?

A

To engage the APU starter.

32
Q

What does the illumination of the “PUMP FAIL” in the APU PWR FUEL switchlight indicate?

A

The APU fuel pump has failed.

33
Q

What is the location of the APU remote cutoff switches?

A
  • External Services Panel
  • APU compartment inside the tail cone
34
Q

What is the function of the APU remote cutoff switches?

A

There are two remote switches that are used to stop the APU in case of an emergency. When either of the two remote switches is selected, a momentary signal is sent to the APU ECU, resulting in an immediate shutdown. Additionally, activation of the “APU FIRE PUSH” switchlight can also cause the APU to shut down.

35
Q

What does the green illuminated “AVAIL” light on the APU panel indicate?

A

The rotor speed is greater than 99% plus 2 seconds and that the APU generator is ready for electrical loading.

36
Q

What does the illumination of the “SOV FAIL” in the APU PWR FUEL switchlight indicate?

A

The APU Fuel Shut Off Valve has failed.

CRJ 700 ENY STUDY GUIDE (17 decks)

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