What keeps a McCauley feathering propeller from feathering when the engine is shut down on the ground?

• A. A spring-loaded latch mechanism prevents the blades moving into the feather position when the engine is shut down on the ground.
• B. Oil pressure remains applied.
• C. The engine braking stops movement.
• D. The propeller automatically locks

Answer: (A)

Feathering a McCauley propeller is controlled by hydraulic pressure moving the blades to a high-pitch angle. When the engine is shut down, oil pressure drops away, so a special feature is needed to prevent the blades from automatically going into feather on the ground. A spring-loaded latch keeps the blades from moving into the feather position when there’s no hydraulic pressure, holding the prop in a safe, non-feathered state until the system is pressurized again or the feather command is actuated. In other words, the latch provides a mechanical lock that prevents unintended feathering on ground shutdown. The other options don’t fit because oil pressure isn’t present after shutdown, engine braking doesn’t control pitch, and a general automatic lock isn’t the specific mechanism used here.