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APU Flashcards

1
Q

Location of the APU

A

On the right side of the MWGB

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2
Q

Purpose of the APU

A

To provide power to the MWGB during ground operations for start and shutdown while the proprotors are not turning.

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3
Q

The ____ reduces the APUs operating speed to match the MWGBs operating speed

A

APU accessory/speed reduction gearbox.

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4
Q

The APU powers the MWGB which in turn powers what systems

A

Electrical, Pneumatic, and Hydraulic systems

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5
Q

How does the APU get fuel

A

Fuel is suctioned from the right feed tank by the APU fuel pump at approx. 300 lb/hour

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6
Q

APU power output

A

300 shp

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7
Q

Location of the APU Control Panel

A

Overhead console

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8
Q

What provides power to start the APU

A

28 VDC electric start motor that gets power from the battery or external power source

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9
Q

APU start limitations

A

Wait 15 seconds before each attempted APU restart. If it fails to start after 3 attempts than allow the start motor 55 minutes before an attempted restart

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10
Q

2 major sections of the APU

A
  1. Power Section2. Gearbox/Reduction Drive Assembly
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11
Q

APU Power section

A

Consists of a constant speed gas turbine with a single stage radial flow compressor, a combustion chamber, and turbine elements

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12
Q

APU Gearbox/Reduction Drive Assembly

A

Reduces APU rpm for use by the MWGB and drives the APU oil and fuel pumps. It houses the reduction drive assembly, accessory drive, integral clutch, and output drive.

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13
Q

APU Ignition and start system

A

Ignition exciter provides 5,000 volts to energize the 2 igniter plugs that ignite the fuel air mixture

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14
Q

5 subsystems of APU

A
  1. Ignition and Start System2. Lubrication System3. Fuel System4. Electronic Control Unit (ECU)5. Event Monitoring System (EMU)
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15
Q

How many chip detectors are in the APU oil system

A

2 located on the bottom of the gearbox reservoir

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16
Q

How many fuel nozzles are there in the APU fuel system

A

2 start nozzles which the ECU signals close and the 6 main fuel nozzles to open

17
Q

ECU

A

Electronic Control Unit - full authority digital controller that performs APU sequencing, condition monitoring, fault isolation, and protection of the APU system.

18
Q

Functions of the ECU

A
  1. Communication with the wing fire protection system to shut down APU in case of fire2. Enables APU to clutch to MWGB after reaching operation temperature or lapsed time interval3. Transmits malfunction indications4. Controls the APU start schedule, fuel flow, turbine speed, and shutdown
19
Q

ECU Automatic Shutdown Criteria

A
  1. Turbine overspeed (103.2%)2. Turbine underspeed (95%)3. Low Oil Pressure (less than 20 +/- 5 psig)4. High Oil temperature (greater than 149 degrees C)5. High EGT6 Midwing Fire detected by wing fire protection system (WFPS)
20
Q

EMU

A

Event Monitoring Unit - houses the hour meter, start counter, pressure transducer, and temperature detector.

21
Q

CRANK position of APU control Panel

A

starter powered rotation without fuel or ignition.

22
Q

CRANK position limitation

A

30 seconds

23
Q

RUN/DISENG position of APU control Panel

A

Performs initial BIT and normal start but does not result in engagement of APU clutch to MWGB

24
Q

RUN/ENGAGE position of APU control Panel

A

Performs initial BIT and normal start and allows the internal clutch to engage the MWGB

25
Q

EMERGENCY RUN/ENGAGE position of APU control Panel

A

Allows ECU to override a detected BIT fault (except overspeed and underspeed) which would otherwise cause and emergency shutdown.

26
Q

With the APU engaged __ of ___ AC Buses are powered. Which ones are not powered

A

4 of 6; the 2 Ice Protection Buses are not powered

27
Q

Why isn’t the APU rated for flight

A

Because it doesn’t have fire detection/suppression

28
Q

During APU Operations the MWGB drives what systems?

A
  1. No. 1 CFG2. Shaft Driven Compressor 3. No. 3 Hydraulic Pump
29
Q

Output driveshaft assembly

A

Splined to the APU on one end and geared to the MWGB on the other end

30
Q

What controls start and main fuel flow control rate to the APU

31
Q

What occurs with failure of the thermocouples that measure APU EGT

A

Results in APU shutdown during normal APU operations, but will remain running during EMERG RUN/ENGAGE

32
Q

What will cause an APU FAIL Advisory

A
  1. APU unable to start due to critical fault or ECU Failure2. APU fails to develop recommended generator rpm3. ECU Communication Failure4. WFPS detects fire5. Fuel valve fault6. Dual thermocouple failure7. Low oil pressure8. High oil temperature
33
Q

Components of the APU Ignition/Start System

A
  1. Ignition Exciter2. Dual Igniter Plugs3. Electric Start Motor
34
Q

What powers the APU ECU

A

Essential Battery Bus

35
Q

APU CHIPS Advisory Procedure

A

Consideration should be given to doing an external power or no APU shutdown.1. APU - OFF

36
Q

APU FAIL Advisory Procedure

A

APU Unable to start due to critical faultIf APU required:1. APU - EMERG RUN/ENGAGE

NR (20 decks)

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