The extension shaft assembly transmits power from the engine to which subsystem?

• A. The reduction gear assembly
• B. Exhaust stack
• C. Hydraulic pump
• D. Environmental control system

Answer: (A)

The extension shaft assembly is the link that carries engine power to the gear reduction system. The engine turns at a very high speed, but the rotor system (the load) needs a much lower RPM with higher torque. The reduction gear assembly takes that high-speed power from the engine and converts it to the appropriate rotor-speed, so the extension shaft is the drive path into that gearbox. Exhaust stack, hydraulic pump, and environmental control system are powered through other engine interfaces (the accessory drive) and aren’t driven by this shaft, whereas the reduction gear assembly is specifically where the engine’s power is reduced to the rotor drive.