FAA Powerplant Written Practice Test

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

1. Counterweights

2. Magnetic locks

3. Latching mechanisms

4. Hydraulic systems

The correct answer is: Latching mechanisms

In a Hartzell Compact propeller, the mechanism that typically prevents feathering when the engine is shut down is a latching mechanism. This latching mechanism is designed to hold the blades in the low-pitch or flat position to ensure that the propeller does not feather unintentionally. When the engine is shut down, the reduction in oil pressure that normally allows the propeller blades to move can trigger the latching system to engage, locking the blades in position. This is critical for maintaining controllability and ensuring that the aircraft has sufficient drag for safe descent and landing procedures. Other mechanisms mentioned, such as counterweights or hydraulic systems, play roles in the operation of the propeller during normal operation, but they do not specifically address the need to prevent feathering during engine shutdown. Magnetic locks are also not typically a feature of the Hartzell Compact propeller design in this context.