APU Flashcards
What is the primary purpose of the auxiliary power unit?
The primary purpose of the APU is to provide electrical power.
Name some things that would cause the APU to automatically shut down on the ground or in flight.
Over speed greater than 106% loss of overspeed protection loss of speed sensor signal No APU rotation No APU light off slow start no acceleration speed fallback APU fire/emergency loss of air inlet APU door failure Uncommanded door closure ECU internal failure loss of DC power
Will the APU shut down on the ground due to high oil temp or low oil pressure?
Yes
Will the APU shut down in flight due to high oil temp or low oil pressure?
No
If the APU shut 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 feet
What is the maximum altitude for APU operation?
Flight level 410
What is the maximum altitude for APU start?
Flight level 370
What is the maximum altitude for APU bleed air extraction?
FL 250
The APU will not start if the APU rpm is rotating above what speed on the ground versus 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 shut down what is the limitation?
Flight is restricted to 220 knots
What are the primary reasons for the speed re-striction?
To prevent the APU from windmilling 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 re-striction 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
What is the purpose of the load control valve?
The LCV varied 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 is the minimum battery voltage for APU start?
22 volts
What are the APU starter limitations?
Maximum of three start per an hour with a two minute cooling period In between
What powers the APU door and what powers ECU?
The APU battery provides power to the 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’t do ground crew shut it down?
Yes through the use of an APU shut off switch on the forward nose or in the APU compartment
What is the absolute APU EGT?
1038’c or lesser value indicated on he EICAS display
What is the maximum APU rpm?
106%
