APU

Question 1

What happens when the APU fuel shutoff button is pressed?

Answer 1

The APU Fuel SOV closes and the APU fuel solenoid valves close (via a request signal).
Reference: OM Vol. 2, Section 2-9 Controls and Indicators

Question 2

What controls the APU?

Answer 2

A FADEC.

Reference: OM Vol. 2, Section 2-9, General

Question 3

What will the APU shut down for automatically on the ground? In flight?

Answer 3

On the ground, essentially any malfunction (Fire, after 10 seconds), in flight, anything not heat related.
Reference: OM Vol. I, Section 2-9, General

Question 4

What is the minimum battery voltage for attempting an APU start?

Answer 4

19.0 V

Reference: OM Vol. 1, Section 3, Receiving Checklist.

Question 5

What power sources may be used to start the APU?

Answer 5

Three power sources may be used to start the APU: a GPU, battery 2 alone or battery 2 assisted by the main generators. Battery 1 cannot be used for APU starting; instead, it is isolated from the load buses to provide stable electrical power for voltage-sensitive equipment.
Reference: OM Vol. 2, Section 2-5, APU Starter-Generator

Question 6

What will occur if a fire is detected in the APU compartment?

Answer 6

An automatic shutdown will occur 10 seconds after a fire is detected or after holding the fire detection test button 10 seconds.
Reference: OM Vol. 2, Section 2-9, General

Question 7

What controls the APU starting sequence?

Answer 7

A dedicated FADEC.

Reference: OM Vol. 2, Section 2-9, General

Question 8

What is the procedure for stopping the APU?

Answer 8

Press the STOP button, monitor deceleration to 0% RPM. At 0% RPM, select the APU master knob to the OFF position.
Reference: OM Vol. 1, Section 3, After Takeoff Checklist

Question 9

What will not cause an APU automatic shutdown in flight?

Answer 9

Any heat-related malfunction. Reference: OM Vol. 2, Section 2-9, General