Which propeller type requires pilot control for pitch adjustment?

The controllable-pitch propeller requires the pilot's input to adjust the pitch of the blades during flight. This type of propeller allows for dynamic changes in blade pitch to optimize performance for various phases of flight, such as takeoff, cruise, and landing. By adjusting the pitch, pilots can improve engine efficiency and aircraft performance in different operating conditions.

In contrast, a fixed-pitch propeller has blades set at a predetermined angle that cannot be changed during flight. This means it does not require pilot intervention to adjust pitch since it remains constant throughout the flight. A constant-speed propeller is a more advanced system that automatically adjusts the pitch based on engine power and speed, minimizing the need for pilot control. A variable-pitch propeller, while it does allow for pitch changes, often includes automatic systems similar to constant-speed propellers, thus not requiring active pilot control in the same way that a controllable-pitch propeller does.