15.18 - APU Flashcards
What type of engine is an APU?
Turboshaft-engine
What are the 6 conditions that cause an APU to Automatically Shutdown?
- High oil temperature
- Low oil pressure
- High EGT (Exhaust Gas Temperature)
- Battery switch off on ground
- Low start EGT
- Load compressor stall
What services does an APU provide and at what altitudes?
Sea level up to 10’000 ft – both electrical and pneumatic power can be used
10’000 to 17’000 ft – Either electrical or pneumatic power can be used (not both)
17’000 to 35’000 ft – Electrical power only
When does an APU reach self-sustaining speed?
95% RPM
What are the purposes for the APU De-Oiling Valve?
- Help to improve the APU start (cold start - viscosity of oil high)
- Reduces load for starter motor and prevents koking of the bearings after shut-down
What are the 2 main purposes of an APU?
To provide electrical and pneumatic power either as backup in flight or if no external networks available at airports.
What type of starter is used on an APU?
An electrical starter motor
What type of compressor is commonly used in an APU?
Centrifugal compressor
(load compressor?)
Where are the most common locations for an APU?
Fuselage tail cone of the aircraft
How is fuel controlled on an APU?
FCB (Fuel Control Unit)
What happens to the APU in an overspeed condition?
It will automatically shut down
Does an APU need a CSD for its generator?
No, CSD is not needed
'’Because the APU generator is not equipped with a Constant Speed Drive (CSD), the gear box speed must be constant to provide a constant APU generator frequency’’
Which tank is the APU fuel taken from?
Main fuel tank
