APU Panel

Question 1

What does the illumination APU MASTER SW FAULT indicate?

Answer 1

Automatic APU shutdown has occurred.

Question 2

What is the significance of the APU AVAIL light illuminating?

Answer 2

APU is running above 99.5 % or 2 seconds after N speed reaching 95%. In practical terms it is ready to accept and support ELEC and/or AIR load.

Question 3

What condition in the APU system would cause an external horn to sound?

Answer 3

APU fire.

Question 4

With the APU green AVAIL light ON and the EXT PWR green AVAIL light on, which system is powering the aircraft?

Answer 4

2 Avails = APU powering the aircraft.

Question 5

If possible, how would the APU be used if it has already started the cool-
down cycle?

Answer 5

Pressing the APU MASTER SW pushbutton.

Question 6

When running the securing checklist, why is it important to wait 2 minutes after the APU avail light goes out before switching off the batteries?

Answer 6

Switching the batteries off before the APU flap is closed may cause smoke in the cabin during the next flight.