APU

Question 1

APU specs

Answer 1

Honeywell 36-150
40 KVA generator
Inlet = Right side (left on 550)
~200 lb/hr burn

vs 550:
- Inlet on right side
- Can assist with eng airstarts below 30k’
- Bleeds off takeoff

Question 2

Max start and operating altitude

Answer 2

37,000’

Question 3

APU generator loading limitations

Answer 3

Limited to 85% between 30-37,000’ at speeds greater than M 0.85

Question 4

When is APU air available?

Answer 4

After reaching 95% RPM for at least 90 sec

Question 5

APU Gen auto powers the bus when?

Answer 5

95% RPM + 4 sec

Question 6

APU Start limitations

Answer 6

Aircraft batts:
3 consec starts, then 1 hour cool down

Ext DC:
Same as Batts, but with a 15 min cool down b/w start attempts to protect aircraft wiring. (Allows electrical feeder cable from the external power receptacle to the APU starter to cool)

Question 7

Surge Control Valve

Answer 7

Prevents compressor stalls. Cycles when the APU is shut down.

> 16,500’ Opens at 60% RPM

Question 8

How many lights/items appear on the APU fire test? What?

Answer 8

(8)
2 Overhead / 4 Master Caution Panel / 2 CAS

Question 9

What does a blinking READY light indicate?

Answer 9

BIT test

Question 10

The APU is capable of driving the Generator when..

Answer 10

95% RPM + 4 sec

Question 11

After APU start and selecting APU BLEED AIR, when does the crossfeed Isolation Valve auto open?

Answer 11

100% RPM + 90 sec

(FSI study guide says 95%)

Question 12

Difference b/w Non-Essential and Essential modes?

Answer 12

Non-Ess = Ground. Protective shutdowns.
Ess= Air. Not all auto shutdowns are active. Remains for 15 min after on-ground if started in air.

Question 13

APU Non-Ess and Ess modes depend upon what system?

Answer 13

WOW

Question 14

What does APU ESSENTIAL CAS mean?

Answer 14

APU operating in ESS Mode
A Non-Ess shutdown signal is sensed
APU will continue operating

Question 15

What CAS msg should not be displayed after APU Fire test?

Answer 15

Fire Bottle Discharged

Question 16

Depressing the APU STOP switch causes the APU…

Answer 16

To shut down by sending an overspeed signal to the ECU.
The overspeed circuit shuts off fuel to the APU at the fuel control unit

Question 17

How do you normally shut down the APU? (What happens)

Answer 17

Press STOP - overspeed signal shuts down the APU
BIT test occurs
Surge Control Valve cycles

Wait until 5% RPM, then turn MASTER off

Question 18

How do you perform an immediate APU Shutdown?

Answer 18

Press MASTER