APU Flashcards
What is the primary purpose of the APU?
The primary purpose of the APU is to provide electrical power.
Name some things that would cause the APU to automatically shutdown on the ground or in flight.
- Overspeed, >106%
- Loss of overspeed protection
- Loss of speed sensor signals
- No APU rotation
- No APU lightoff
- Slow start
- No acceleration
- Speed fallback
- APU fire/emergency
- Loss of air inlet
- Uncommanded door closure
- ECU internal failure
- Loss of DC power
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
If the APU shuts down automatically due to fire on the ground will the bottle fire?
Yes
If the APU shuts down automatically due to fire in flight will the bottle fire?
No
At what altitude will the surge control valve open?
17,000’
What is the maximum altitude for APU operation?
FL410
What is the maximum altitude for APU start?
FL370
What is the maximum altitude for bleed air extraction?
FL250
The APU will not start if the APU rpm is rotating above what speed on the ground verses in flight?
5% on the ground, and 12% in flight.
If the APU door is open or the door position is unknown with the APU shutdown, what is the limitation and why?
Flight is restricted to 220 KIAS.
To prevent the APU from wind-milling without the proper lubrication, and to ensure the APU RPM remains below 12% in the event it becomes necessary to start the APU in flight.
Is there a way around the 220 knot restriction with the APU door open?
Yes. Normal speeds can be used if the APU is running.
What provides fuel to the APU?
A dedicated 28 VDC pump feeding from the left collector tank.
If the APU fuel pump fails will the APU continue to operate?
Yes, but it cannot be restarted without the pump.
