Auxillary Power Unit Flashcards
How much battery voltage is required to start the APU?
22 volts on both the main and APU batteries but it only takes the APU battery to actually start
What is the normal and non normal APU door indications.
Normal = DOOR OPEN or DOOR CLOSED on the status page
What is the APU interlock?
A function that prevents against back flow from the engines by closing the APU
What are the differences between an APU fire on the ground verse in the air
On the ground = bottle fires automatically
In the air = pilot controlled
What will occur if the APU pump fails while the APU is still in operation?
The APU solenoid pump pulls fuel to the APU
Why would it be normal to see a L AUTO XFLOW message while sitting at the gate with the APU running?
PSM 04-30-1
The APU pulls off the left collector tank
What’s the primary purpose of the APU?
Electrical power
What indications would you find with an APU pump failure?
Yellow outline of pump
APU Pump caution light
What is the critical rotation speed of the APU
An RPM that is fast enough to require oil but to slow to draw oil through the system.
5 - 30%
When does the APU door open
On the ground with PWR/fuel switch
In the air with the APU Start/Stop switch button
When can you restart the APU after it’s been normally shut down?
Gauges go away
Inbite test is complete
2 minutes rest
Which pump provides pressurized fuel to the APU?
PSM 04-30-1
APU fuel pump
What does the green AVAIL light indicate on the APU START/STOP push button?
The APU is ready for electrical and pneumatic loading.
After the APU completes the start and is stabilized, what do you check?
Voltage frequency and loads are normal
When might you get an APU GEN OFF caution message?
APU GEN is selected off and the APU is ready to load
