What is the primary role of the prop feathering mechanism in case of oil loss?

The primary role of the prop feathering mechanism is to reduce drag on the engine in the event of oil loss. When oil pressure is lost, the feathering mechanism moves the propeller blades into a position that creates minimal aerodynamic resistance. This is crucial for improving the overall performance of the aircraft, especially in a single-engine failure scenario, as it helps maintain control and allows the remaining engine(s) to operate more efficiently without the added drag from a windmilling propeller. By positioning the blades edge-on to the airflow, feathering significantly decreases drag, enhancing the aircraft's glide ratio and allowing for better recovery and landing options.

In contrast, the other choices do not accurately reflect the function of the prop feathering mechanism. While allowing the prop to spin freely, stopping the prop entirely, and adjusting engine thrust may all be related to propeller operation, they do not encapsulate the primary purpose or function of feathering during oil loss situations. Therefore, the correct answer highlights the essential role of drag reduction in maintaining aircraft controllability and performance.