Where does an air-turbine starter get air for starting on a jet transport aircraft?

Where does an air-turbine starter get air for starting on a jet transport aircraft?

• A. From an APU.
• B. From a GPU.
• C. From a running engine.
• D. From an APU, GPU, or from a running engine.

Answer: (D)

Air-turbine starters rely on bleed air to spin the engine’s starter turbine and bring the engine up to speed for light-off. That bleed air can come from several sources, and the system is designed to accept any of these as long as the pressure and flow are adequate. One source is the onboard auxiliary power unit, which provides bleed air when the main engines aren’t running. Another source is a ground power unit that supplies external compressed air when the aircraft is on the ground. A third option is cross-bleed air from a running engine; once one engine is running, its bleed air can be routed to start the other engine. Because all three sources are usable, the air-turbine starter can be fed from an APU, a GPU, or a running engine.

Air-turbine starters rely on bleed air to spin the engine’s starter turbine and bring the engine up to speed for light-off. That bleed air can come from several sources, and the system is designed to accept any of these as long as the pressure and flow are adequate.

One source is the onboard auxiliary power unit, which provides bleed air when the main engines aren’t running. Another source is a ground power unit that supplies external compressed air when the aircraft is on the ground. A third option is cross-bleed air from a running engine; once one engine is running, its bleed air can be routed to start the other engine. Because all three sources are usable, the air-turbine starter can be fed from an APU, a GPU, or a running engine.