APU

Question 1

What are the Primary Purposes of the APU?

Answer 1

Ground - Electrical power and bleed air before engine start. Electric power has priority over bleed air.
Inflight - Electrical Power available through aircraft envelope, and bleed air up to approximately 17,000’

Question 2

How do you monitor the APU Start? Do you Have to?

Answer 2

• Status Page

- No, because auto protected.

Question 3

How many batteries do you need to start the APU

Answer 3

2

• A/C Battery for Fire Detection, APU Fuel Valve, and DC Fuel Pump, and APU Control Circuitry
• APU Battery APU Inlet Door, APU Starter, and APU Control Circuitry.

Question 4

Which Fuel tank provides fuel for APU and how does it get to the APU.

Answer 4

Left.

• Unpowered A/C - The Left DC Fuel Pump. (Until AC Power available, then L FWD AC Pump.)
• Powered A/C - The Left Forward AC Pump. Confirmed by extinguishing of L FWD PRESS Light.

Question 5

Describe the APU Start Sequence.

Answer 5

• Rotate and hold in START.
• FAULT Light Blinks once (Fuel Valve Opening).
• RUN Light Binks twice for an internal test.
• RUN Light Illuminates indicating a stable start.
• If there is a bleed air demand, the APU will automatically take that load.
• If there is external power, the APU will not automatically supply power; if it is removed, the APU will automatically take that load. (EXT PWR has priority.)

Question 6

APU Starter Limitations

Answer 6

• 3 attempts within a 60 minute period, allowing 1 Minute

Question 7

APU Shutdown.

Answer 7

• Move knob to OFF.
• Removes Bleed Load, ~1 minute cool down, then it will shut down.
• To cancel the shutdown sequence, (while RUN light is still ON) you can move the knob back to START, (unless the RUN light has already gone out.)

Question 8

APU Considerations for A/C Shutdown.

Answer 8

• Turning the BATT Switch OFF (on the ground) causes an APU Shutdown. There will not be Fire Detection while the APU shuts down. Not in checklist. You should wait two minutes.

Question 9

APU Auto Shutdown

Answer 9

• Fire
• Overspeed
• high EGT
• Low Oil Pressure
• High Oil Temp

Question 10

APU FAULT Light.

Answer 10

• Fault in System
• (per Checklist) Turn OFF
• FAULT light will reset (because OFF resets circuitry)
• FAULT will only remain illuminated if the APU Fuel valve didn’t close.

Question 11

What does rotating the APU slector to START do?

Answer 11

• Begins Automatic Start sequence. (Self Test)(RUN Blinks)
• APU Fuel Valve Opens (FAULT light Blinks), and APU Door begins to open.
• DC or AC Fuel Pump energized depending on Power availability.
• When APU Door is open, electric starter engages.
• RPM, FUEL, IGN, Acceleration..
• APU Run light illuminates and APU is usable.