FAA Powerplant Written Practice Test

What mechanism prevents a Hartzell Compact propeller from feathering when the engine is shut down on the ground?

1. Latching mechanisms

2. Spring tension

3. Pressure differentials

4. Brake systems

The correct answer is: Latching mechanisms

The mechanism that prevents a Hartzell Compact propeller from feathering when the engine is shut down on the ground is primarily the latching mechanisms. These mechanisms are specifically designed to hold the blades in place and ensure they remain in a fixed position during situations where feathering would not be appropriate, such as when the aircraft is on the ground. Feathering is the process of adjusting the propeller blades to a position that minimizes drag, typically used during engine failure and flight maneuvers. However, when the aircraft is on the ground, it is crucial that the propeller remains in a non-feathered position to avoid unnecessary drag during taxi and to ensure proper operation during engine start. While spring tension, pressure differentials, and brake systems are important components within the propeller control mechanism, they do not serve the primary function of holding the blades in place against feathering when the engine is not running. Spring tension may aid in returning blades to a particular position, pressure differentials are involved in the operation of the pitch control, and brake systems are related to stopping mechanical movement, but none specifically provide the direct latching function that keeps the blades secured in the appropriate angle on the ground like the latching mechanisms do.