APU Flashcards
What types of APUs do we have?
Turbomach/Sundstrand APU
Garret APU
What does the APU do?
It provides pneumatic power for starting the engines and operating the Environmental Control System (ECS)
What does the APU consist of?
It is a gas turbine engine with a power section, a reduction gearbox, appropriate controls, and accessories.
Fuel consumption at rated power is ___.
150 lbs per hour
Operations of the APU in flight (should/shall) be limited to ___.
Shall
essential operations only
What are the acceptable in-flight uses of the APU?
- EPs
- Single-engine training
- practice autorotations
- powering the ECS during extreme temperature operations
What are the APU system accessories?
- prime/boost pump
- hydraulic accumulator (with hand pump)
- hydraulic starter
- ac generator
What does the prime boost pump do?
Used to prime the engine or APU fuel lines.
Also provides fuel under pressure to the APU during starting and operations at pressure altitudes above 8000 ft
What does the hydraulic accumulator do?
provides the hydraulic pressure for driving the APU starter
What is the minimum accumulator pressure required for starting the APU?
2650 psi
With AC power available, the accumulator is charged by the ____.
backup hydraulic pump
What is the APU controlled and monitored by?
Electronic Sequence Unit (ESU) or Digital Electronic Sequence Unit (DESU)
Will automatically shut down the APU if a start sequence fails or a monitored parameter is exceeded during operation (exception of APU OIL TEMP HI)
The DESU for the Turbomach/Sundstrand APU has the added capability to control what?
APU overtemperatures by regulating the main fuel valve and start bypass valve
What does APU FAIL mean?
APU has failed due to:
- High/Low Ng
- High/Low TGT
- Low Oil Pressure
- Start sequence failure
Where is fuel supplied from for the APU?
The right fuel cell by the prime/boost pump
When does the APU ACCUM LOW advisory appear?
when accumulator pressure drops below 2650 psi
What happens when you place the APU GENERATOR switch to ON?
Makes electrical power available
If APU does not start and the APU ACCUM LOW advisory light is not illuminated, how do you attempt a start?
What happens once you do this?
A start may be attempted by simultaneously moving the APU CONTR switch to ON and actuating the manual START/OVERRIDE lever located on the Accumulator Manifold.
APU accum pressure will be dumped to the starter to turn the compressor until the APU has reached a self-sustaining speed.
If the backup pump is cycled ON then to the OFF or AUTO position, it will remain on for one cycle of __. (__ with winterization kit installed.)
90 seconds
180 seconds
(From Ch. 3) What happens if you fill the Turbomach/Sundstrand APU to the full line?
It will cause the APU to overheat
Why start APU on ground?
WARNING
APU does not incorporate compressor or turbine wheel containment device. Uncontained APU failure may result in injury to ground personnel and/or damage to flight critical components including tail rotor drive shaft
