Which option is NOT a permissible source for starting an engine?

Which option is NOT a permissible source for starting an engine?

• A. Bleed air from the APU
• B. External ground cart
• C. The other engine
• D. Hydraulic pressure from the aircraft hydraulic system

Answer: (D)

Engine starting relies on supplying energy to the air turbine starter with compressed energy, not hydraulic power. The usual sources are bleed air from the APU, bleed air cross-bleed from another running engine, or an external ground air source that provides high-pressure air to drive the starter. These options are designed specifically to spin up the engine by driving the turbine with pressurized air. Hydraulic pressure from the aircraft’s hydraulic system isn’t used to start engines because hydraulics power actuators and flight controls, not a turbine starter. There isn’t a ready-to-use hydraulic energy source intended to drive the engine’s starter, and using hydraulic pressure could cause contamination, improper actuation, or damage. So the hydraulic system is not a permissible starting source.

Engine starting relies on supplying energy to the air turbine starter with compressed energy, not hydraulic power. The usual sources are bleed air from the APU, bleed air cross-bleed from another running engine, or an external ground air source that provides high-pressure air to drive the starter. These options are designed specifically to spin up the engine by driving the turbine with pressurized air.

Hydraulic pressure from the aircraft’s hydraulic system isn’t used to start engines because hydraulics power actuators and flight controls, not a turbine starter. There isn’t a ready-to-use hydraulic energy source intended to drive the engine’s starter, and using hydraulic pressure could cause contamination, improper actuation, or damage. So the hydraulic system is not a permissible starting source.