Auxiliary Power Unit Flashcards
The APU is equipped with a dedicated FADEC.
T or F
True
When are electrical and pneumatic loading available during an APU start?
When the APU has reached 95% RPM plus 3 seconds.
During the normal shutdown sequence, APU bleed air is immediately removed and electrical power is removed after a 1 minute cool down period, followed by a spool down period.
(T or F)
True
In flight the APU automatically shuts down for:
- Overspeed
- Underspeed
- FADEC critical fault
What is the APU used for?
- Electrical power
2. Bleed air
What monitors and controls the APU?
It’s own dedicated FADEC
How is Battery 2 used for APU start?
It powers the APU start bus.
What is the fuel source for the APU?
Right Fuel Tank or Left Fuel Tank through the Crossfeed Valve
What Fuel Pump is used for APU Start with Batteries ON only?
DC Fuel Pump
What fuel pump is used for APU start with an AC powered aircraft?
AC Fuel Pump 2
What fuel pump is used for APU start with only the Right Engine running?
Right Ejector Fuel Pump
Will the APU shut down automatically if the APU fails to start within the normal start cycle time period?
Yes
What does moving the APU Selector knob to OFF do?
Initiates a normal APU shutdown with a 1-minute cool down
Can the APU pneumatics be used during the cool down period?
No
Can the APU electrical power be used during the cool down period?
Yes
If you need the APU 50 seconds into shutdown is there a way to stop the shutdown?
Yes, turn the APU Master knob to ON
How can the APU be shutdown immediately?
Push in the guarded APU EMER STOP button
What conditions will the APU automatically shutdown on the ground?
- Overspeed
- Underspeed
- FADEC critical fault
- APU fire
- APU high oil temp
- APU low oil pressure
- APU EGT over-temp
- Sensor fail
When does the Red Bar on the APU EMER STOP button illuminate?
When an APU fire has been detected.
What happens when the APU EMER STOP button is pushed in?
- The APU fuel shutoff valve closes and;
2. The APU shuts down without a cool down period.
During normal operations on the ground with the APU running, it is normal to see the fuel unbalanced with less fuel in which tank?
Right fuel tank
What is the altitude limit for an APU start? [SOP Limitation]
30,000’
The operational altitude limit for the APU is? [SOP Limitation]
33,000’
What is the APU operational limit for bleed air? [SOP Limitation]
15,000’
What is the APU operational limit to assist an engine start? [SOP Limitation]
21,000’
