APU

Question 1

Location of the APU

Answer 1

On the right side of the MWGB

Question 2

Purpose of the APU

Answer 2

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

Question 3

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

Answer 3

APU accessory/speed reduction gearbox.

Question 4

The APU powers the MWGB which in turn powers what systems

Answer 4

Electrical, Pneumatic, and Hydraulic systems

Question 5

How does the APU get fuel

Answer 5

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

Question 6

APU power output

Answer 6

300 shp

Question 7

Location of the APU Control Panel

Answer 7

Overhead console

Question 8

What provides power to start the APU

Answer 8

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

Question 9

APU start limitations

Answer 9

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

Question 10

2 major sections of the APU

Answer 10

1. Power Section2. Gearbox/Reduction Drive Assembly

Question 11

APU Power section

Answer 11

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

Question 12

APU Gearbox/Reduction Drive Assembly

Answer 12

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.

Question 13

APU Ignition and start system

Answer 13

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

Question 14

5 subsystems of APU

Answer 14

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

Question 15

How many chip detectors are in the APU oil system

Answer 15

2 located on the bottom of the gearbox reservoir

Question 16

How many fuel nozzles are there in the APU fuel system

Answer 16

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

Question 17

ECU

Answer 17

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

Question 18

Functions of the ECU

Answer 18

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

Question 19

ECU Automatic Shutdown Criteria

Answer 19

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)

Question 20

EMU

Answer 20

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

Question 21

CRANK position of APU control Panel

Answer 21

starter powered rotation without fuel or ignition.

Question 22

CRANK position limitation

Answer 22

30 seconds

Question 23

RUN/DISENG position of APU control Panel

Answer 23

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

Question 24

RUN/ENGAGE position of APU control Panel

Answer 24

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

Question 25

EMERGENCY RUN/ENGAGE position of APU control Panel

Answer 25

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

Question 26

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

Answer 26

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

Question 27

Why isn't the APU rated for flight

Answer 27

Because it doesn't have fire detection/suppression

Question 28

During APU Operations the MWGB drives what systems?

Answer 28

1. No. 1 CFG2. Shaft Driven Compressor 3. No. 3 Hydraulic Pump

Question 29

Output driveshaft assembly

Answer 29

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

Question 30

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

Answer 30

ECU

Question 31

What occurs with failure of the thermocouples that measure APU EGT

Answer 31

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

Question 32

What will cause an APU FAIL Advisory

Answer 32

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

Question 33

Components of the APU Ignition/Start System

Answer 33

1. Ignition Exciter2. Dual Igniter Plugs3. Electric Start Motor

Question 34

What powers the APU ECU

Answer 34

Essential Battery Bus

Question 35

APU CHIPS Advisory Procedure

Answer 35

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

Question 36

APU FAIL Advisory Procedure

Answer 36

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