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