What happened
The pilot, who was also the aircraft's mechanic, was conducting an in-flight rigging check when a popping sound occurred during the climb. This was immediately followed by a total loss of propeller thrust. The pilot found that moving the propeller control had no effect on the engine's performance, necessitating an emergency descent.
To maintain an airspeed of 85 knots during the approach to a road, the pilot had to maintain a nose-down attitude of 35 to 40 degrees. During the forced landing, the engine was not secured by the pilot. The aircraft experienced a hard landing with an estimated descent rate of 1,800 feet per minute.
The investigation
Upon inspection, the propeller system was disassembled, revealing that two staking pins were missing. The investigation found that the guide collar, rod, fork, and piston had rotated around the hub. Additionally, the propeller blades had become disconnected from the pitch change mechanism. Records indicated that the propeller assembly had been overhauled and installed on the aircraft approximately 31.7 hours before the failure.