FAA Aviation Mechanic Powerplant (AMP)Ignition and Starting SystemsMedium
A large turbofan engine on the ramp is being started using ground air supplied through a hose to the starter. Which starting system is being used, and how does it turn the engine?
- AA direct cranking electric starter that uses ground battery power to turn the compressor directly
- BA cartridge starter that ignites a solid propellant charge to spin the accessory gearbox
- CAn air turbine starter that uses compressed air to spin a small turbine connected through reduction gearing to the engine
- DA hydraulic starter that uses hydraulic fluid pressure supplied from the ground cart to rotate the compressor
Show answer & explanationAnswer & explanation
Correct answer: C. An air turbine starter that uses compressed air to spin a small turbine connected through reduction gearing to the engine
An air turbine starter uses high-pressure air (from an APU, ground cart, or cross-bleed from another engine) directed onto a small turbine wheel; the turbine's rotation is passed through reduction gearing to the engine's accessory drive to crank it for starting.
Why the other options are wrong
- A. Electric starters use electrical current, not compressed air.
- B. Cartridge starters use a pyrotechnic charge, not compressed air from a hose.
- D. Hydraulic starters use fluid pressure, not compressed air.
Air Turbine Starter
A pneumatic starting device that uses compressed air to spin a small turbine wheel geared to the engine's accessory drive, commonly used on turbojet and turbofan engines.
- Air source can be APU, ground cart, or engine cross-bleed
- Includes reduction gearing and often a clutch that disengages after start
- Lightweight compared to electric starters for large engines
Memory trick: Air turbine starter = 'Blow it to go' — compressed air spins the turbine