APU Flashcards
APU
Single-Stage gas turbine engine
APU provides what?
Pneumatic air and AC power
Does the APU have its own FADEC?
Yes
APU is normally fed from which wing tank?
Right wing tank
Can the APU be fed from the left tank?
Yes, via the crossfeed
What provides pressure if DC power only?
DC fuel pump will supply fuel pressure
If AC power is available and the engine is not running what provides pressure?
AC fuel pump
APU bleed air provides pneumatic air for what?
- Air conditioning
- Pressurization
- Water pressurization
The FADEC monitors and will command auto shutdown in flight for what conditions?
Over-speed, under-speed and FADEC critical fault
Automatic shutdown on ground for which conditions?
- Over-speed
- Under-speed
- FADEC critical fault
- Fire
- Overheat
- Low oil pressure
- High oil temperature
- Sensor failure
APU selector knob controls?
Normal start and shutdown
APU selector knob to OFF?
Removes pneumatics only, placing the APU into a 1-minute cool down period before shutting down
-Can be cancelled by reselecting to ON within 1 minute
EMER STOP button is used for what?
Abnormal shutdown without a 1 minute cool down period
At what % is electrics and pneumatics usually available after the APU is started?
95%
What kind of APU does the aircraft have?
Sundstrand APS 2300
Describe the APU?
Constant speed, Single-stage impeller with 2-stage axial-flow turbine with independent oil system
What controls the APU?
A dedicated FADEC
What battery is used for APU start?
BATT 2 powers the starter
BATT 1 powers the FADEC and EICAS for monitoring
What is the fuel source for the APU?
The right tank, left tank through the cross-feed valve
What fuel pump is used for APU start?
- Batteries “ON” only DC fuel pump in right tank
- AC powered airplane with 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, with 1-minute cool down, no pneumatics, electrics only
Can the APU shutdown be cancelled?
Yes, by moving start switch back to ON before the 1-minute cool down is over
How is the APU shut down immediately?
APU emergency stop button (no 1-minute cool down)
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?
- Overspeed
- Underspeed
- FADEC critical fault
- Fire
- Overheat
- Low oil pressure
- High oil temp
- Sensor failure
When will automatic shutdown of the APU occur in flight?
- Overspeed
- Underspeed
- FADEC critical fault
Can the APU be started after a critical fault?
No
