APU

Question 1

APU gas turbine generator

• what kind of power does it supply
• limitation on bleed air
• how is it controlled
• limitation while deicing

Answer 1

• DC Power - 28vDC, 400 amps (ground operations only)
• Provides Bleed Air for “Air Conditioning Packs” (ground operations only)
• Controlled by its own FADEC
• Can NOT de-ice with APU ON (on ground)

Question 2

APU Fuel Supply

• where is fuel fed from
• what button opens the APU fuel sov and when will it close
• the APU fuel sov will close automatically if any of the following occur (7)

Answer 2

• Fuel is fed from the LEFT wing fuel collector bay
• APU fuel shutoff valve OPENS when the APU PWR switchlight is pushed and CLOSES when the APU is shut down
• The APU fuel shutoff valve will automatically close if any of the following should occur:
  • The PWR switchlight is pushed off
  • An APU fire is detected
  • EXTG switchlight on the APU section of the Fire Protection Panel is pushed
  • APU FIRE TEST button is pushed
  • Aircraft becomes airborne while the APU is still running
  • An APU fault is detected
  • Starter-Generator overheats (the GEN OHT advisory light illuminates)

Question 3

APU Electrical System

• what voltage is the generator and where is it mounted
• what power is needed for a start
• to what % will the started remain engaged

Answer 3

• 28vDC Generator mounted on the APU Gearbox
• APU start requires either aircraft battery power or an external DC power source
• Starter mode remains engaged until the APU reaches 50% operating speed

Question 4

APU bleed air

- Provides bleed air for: (2)

Answer 4

• ECS (ground operations only)

- Holds the “Aft Safety Valve’ Open (ground operations only)

Question 5

APU FADEC

- The FADEC monitors critical/major faults and will command shutdown based on: (9)

Answer 5

• Overspeed
• Underspeed
• Start Failure
• Acceleration Failure
• EGT Overtemperature
• High Oil Temperature
• Low Oil pressure
• Failed Sensors
• Internal Failure