APU

Question 1

What does the illumination of the APU MASTER SW FAULT light indicate?

Answer 1

An automatic APU shutdown has occurred

Question 2

What is the significance of the APU AVAIL light illuminating?

Answer 2

APU is available: either above 99.5% or 2 seconds after reaching 95% — ready to support ELEC and/or AIR

Question 3

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

Answer 3

APU fire

Question 4

With both APU AVAIL and EXT PWR AVAIL lights on, which power source is supplying the aircraft?

Answer 4

The APU — “2 AVAILS = APU powers aircraft”

Question 5

If the APU has already started its cool-down cycle, how can it be used again?

Answer 5

Press the APU MASTER SW pushbutton to reinitiate operation

Question 6

Why is it important to wait 2 minutes after the APU AVAIL light goes out before switching off batteries?

Answer 6

To avoid cabin smoke during the next flight due to the APU flap not fully closing

Question 7

If one generator fails, what is the maximum altitude to start the APU?

Answer 7

FL410

Question 8

If the aircraft is in emergency electrical configuration, what is the maximum APU start altitude?

Answer 8

FL250

Question 9

Above what altitude can the APU no longer supply bleed air for single pack operation?

Answer 9

22,500 ft for Honeywell APU; 20,000 ft for Hamilton Standard APU (check FCOM to confirm type)

Question 10

Can you use APU bleed air for wing anti-ice?

Answer 10

No, it is not permitted