APU Flashcards
What RPM range will the APU starter cutout?
Gnd: 46%
Flight: 46 - 60%
What are the APU starter limits?
3 attempts in 1 hour with 2 minutes cool down between each start attempt.
What will the APU automatic fire protection provide in flight?
Automatic shutdown of the APU, no automatic discharge of the bottle
Where does the fuel to operate the APU come from?
From the Lt Collector tank, via a dedicated 28V DC pump
Prior to APU start, what should the minimum battery voltage be?
22V on both the APU BATT DIR BUS and
MAIN BATT DIR BUS
The APU ECU will inhibit start if the APU rotates above ___% in flight and ____% on the ground.
12% in flight
5% on the groundand
Max altitude for APU start?
37,000 ft
Max altitude for APU operation?
41,000 ft
Max altitude for Bleed Air extraction?
25,000 ft
Can the APU be used as a source of bleed air for ice protection?
No
If the APU door is stuck open or it’s position is unknown, what must be done?
- Max airspeed of 220 knts OR
- run the APU continuously with no speed restriction.
Describe the APU door
Ground: Door id closed at 0 degrees when OFF and
45 degrees when running
Flight: Door modulates between 0 and 45 degrees
What is the APU’s main priority?
Electrical power: 115 VAC, 400Hz, 40 KvA
APU Bleed air is controlled by modulating what?
APU LCV (Load control valve)
If the APU electrical fuel pump FAILS while the APU is running, will the APU continue to run?
Yes. But the APU will not start once it is shut down.
Will the APU shutdown on the ground due to High oil Temp or Low oil pressure?
Yes
Will the APU shutdown in flight due to High oil Temp or Low oil pressure?
No
Will the APU automatically shutdown on the ground due to fire, and will the bottle automatically fire?
Yes
Yes
Will the APU automatically shutdown in flight and will the bottle automatically fire?
Yes
No
At what altitude will the surge valve open?
17000’
Name 14 things that would cause the APU to automatically shutdown.
- APU Fire
- APU Door failure
- ECU Internal failure
- Loss of DC Power
- Loss of air inlet
- Loss of over speed protection
- Loss of speed sensor signals
- No APU Acceleration
- No APU Rotation
- No APU Light-off
- Overspeed > 106%
- Slow start
- Speed fallback
- Uncommanded door closure
What is the purpose of the Load control valve? (LCV)
The LCV varies pneumatic load to ensure electrical power and 45 psi in the manifold
Can APU bleed air be used by the anti-ice system?
No
What powers the APU door?
What powers the ECU?
The APU Battery provides power to the APU door and is secondary for the ECU
The MAIN Battery is the primary power source for the ECU
If the APU is left unattended, can the ground crew shut it down? Where?
Yes. APU shutoff switch on the forward service panel, or in the AFT equipment bay
