APU Flashcards
What will cause an immediate APU shutdown in attended mode?
- Inlet door failed closed
- APU Controller fault
- Start failure
- Overspeed or loss of Overspeed protection
- Speed droop
- APU fire or inlet overtemperature
When is the APU is Attended Mode?
With either engine running or in flight.
During an APU start on battery power, which starter(s) are used?
Only the right starter.
How many APU start attempts are made by the system on APU battery power?
Two consecutive start attempts, then a 5 minute cool down.
Are both batteries required for APU start?
Both batteries required.
When starting APU from an unpowered airplane, what must the APU controller wait for before proceeding with APU start?
APUC waits until CCS applications are available before proceeding with the start. Fire detection and fuel management applications are necessary.
If an APU start fails, will an EICAS message display?
EICAS “APU SHUTDOWN” advisory
If AC power is not available for APU start, what is the source of APU fuel?
Dedicated DC fuel pump in the left tank, powered by the main battery.
Once AC power is available, which pump supplies fuel pressure to the APU?
Fuel supplied by the left manifold by any AC pump. Left AFT AC pump commanded on with AC power available and APU switch on.
What is the operating ceiling limit for the APU?
APU can be started and operated to the airplane maximum certified altitude.
What is the max altitude the APU can be started with no fuel pumps operating?
14.000’
When does the APU automatically start?
In flight, when three or more engine generators go offline.
When APU automatic start condition is valid, what is the only way of shutting down the APU?
By pulling the APU fire switch.
What faults will cause the APU to shut down in the unattended mode?
- Inlet door failed closed
- APU Controller fault
- Start failure
- Overspeed or loss of Overspeed protection
- Speed droop
- APU fire or inlet overtemperature
- High EGT / loss off signal
- High oil temperature
- Low oil pressure
- ASG oil filter approaching bypass
Is there a cooldown period for automatic APU shutdowns?
No
For which faults will the APU continue to run with EICAS caution message?
EICAS “APU LIMIT”
- High EGT
- High oil temperature
- Low oil pressure
In flight with an APU fire, will the APU fire bottle automatically discharge?
Yes, in flight or on the ground with a 15sec delay.
What indication is given when the APU is running?
EICAS memo “APU RUNNING”
When does the APU cool down timing begin?
When the APU selector is set to OFF.
How long is the APU cool down time and is there any indication?
2 minutes
EICAS “APU COOLDOWN”
What happens at the end of the cooldown time to accomplish a final shutdown?
An APU Overspeed is simulated to test the Overspeed and fuel shutoff protection.
What APU functions are powered by the APU battery?
APU battery powers APU controller, air inlet door, and right starter.
Which APU functions are powered by the main battery?
Main battery powers APU fuel shutoff valve, DC fuel pump and fire detection system.
