How is the propeller feathering pump on a hydromatic propeller powered?

• A. A separate hydraulic pump powered by the engine
• B. The holding coil on the feathering button switch holds a solenoid relay closed
• C. Electrical power from the generator
• D. Pneumatic pressure from the compressor drives the pump

Answer: (B)

Feathering a hydromatic propeller is driven by an electric feathering pump. When you press the feather switch, electrical power from the generator flows to a holding coil in the switch, which keeps a solenoid relay closed. This latches the circuit so the feathering pump continues to run and push hydraulic oil to rotate the blades toward the feather position. The holding coil’s latch action lets you release the switch while the pump completes the feathering, without needing to hold the switch continuously. The design uses electrical power, not a separate engine-driven hydraulic pump or pneumatic air from the compressor, to power the feathering pump.