APU Flashcards
What is an APU?
A single-stage gas turbine engine that provides pneumatic air and AC power.
Controlled by its own FADEC.
How is the APU fuel supply normally fed?
Normally fed from the right wing tank.
Can also be fed from the left tank via the crossfeed valve (XFEED LOW 2).
What supplies fuel pressure if AC power is available and the engine is not running?
The AC fuel pump provides fuel pressure.
What does the APU bleed provide air for?
Air conditioning, pressurization, and water pressurization.
What does the FADEC monitor for APU operation?
Critical/major faults and will command shutdown based on specific conditions.
What are the automatic shutdown conditions in flight?
Overspeed, underspeed, and FADEC critical fault.
What are the automatic shutdown conditions on the ground?
Overspeed
underspeed,
FADEC critical fault,
fire,
overheat,
high oil temperature,
low oil pressure,
sensor failure.
How is normal start/shutdown controlled for the APU?
By the APU selector knob.
What happens when the APU selector knob is set to ‘OFF’?
Removes pneumatics only, placing the APU into a 1-minute cool down period before shutting it down.
How can you cancel the shutdown during the cool down period?
Reselect the selector knob to the ‘ON’ position within 1 minute.
What is the purpose of the EMER STOP button?
Used for an abnormal shutdown without a 1-minute cool down period.
When will electrics and pneumatics be available after starting the APU?
Usually around 95% plus 3 seconds after the APU is started.
What kind of APU is on the aircraft?
Sundstrand APS 2300
Describe the APU.
Constant speed
Single-stage impeller with a 2-stage axial-flow turbine
Independent oil system
Does a FADEC control the APU
YES
What battery is used for the APU start?
BATT 2 powers the starter
BATT 1 powers the FADEC and EICAS for monitoring
What is the fuel source for the APU?
Right fuel tank
Left fuel tank through the crossfeed valve
What fuel pump is used for APU start?
Batteries ‘ON’ only DC fuel pump in right tank
AC powered airplane ACMP 2
Right engine running Ejector fuel pump
Will the APU shutdown automatically if speed and acceleration rate isn’t reached in starting cycle time?
Yes
What does moving the APU start switch to ‘OFF’ do?
Initiates normal APU shutdown
1-minute cool down
No pneumatics (electrics only for 1 minute)
Can the APU shutdown be cancelled?
Yes, by moving the START switch back to ‘ON’ before the 1-minute cool down is over
How is the APU shutdown immediately?
APU emergency stop button
No 1-minute cool down period
What will happen if batteries are turned OFF during the 1-minute cool-down period?
APU will shut down immediately
When will automatic shutdown of the APU occur on the ground?
Automatic shutdown of the APU on the ground will occur due to:
- Overspeed
- Underspeed
- FADEC critical fault
- Fire
- Overheat
- High oil temperature
- Low oil pressure
- Sensor failure
When will automatic shutdown of the APU occur in flight?
Automatic shutdown of the APU in flight will occur due to:
- Overspeed
- Underspeed
- FADEC critical fault
Can the APU be started after a critical fault?
No
