What is done to cause a hydromatic propeller to feather?

• A. High-pressure engine oil is directed into the propeller through the governor.
• B. Low oil pressure is used to retract the blades.
• C. Electrical power is supplied to the feathering actuator.
• D. The propeller automatically switches to feather when RPM drops.

Answer: (A)

Feathering a hydromatic propeller is accomplished by using engine oil pressure to move the blade-pitch mechanism to the feather position. When the pilot commands feather, a valve opens and high-pressure oil is directed into the propeller hub through the governor. This pressure pushes the internal piston, rotating the blades toward a high-angle, feathered position to minimize drag in an engine-out condition.

That’s why directing high-pressure oil to the propeller is the correct method. Using low oil pressure would not drive the blades to feather, electrical power isn’t the standard means for a hydromatic propeller’s feathering, and feathering is a commanded action rather than something that automatically happens just from RPM changes.