What happened
During cruise flight, the pilot reported experiencing a severe vibration within the aircraft. In response to this mechanical issue, the pilot initiated a forced landing procedure. During the execution of this emergency landing, the airplane collided with terrain and subsequently came to rest in an upright position.
The investigation
Following the accident, investigators conducted a detailed examination of the aircraft's propulsion system. A critical finding was that a pitch change knob on one of the propeller blades had failed. To determine the root cause of this component failure, a metallurgical examination was performed on the broken part.
Findings
The metallurgical analysis revealed that the pitch change knob failed due to fatigue. This mechanical failure is identified as the primary factor leading to the severe vibration reported by the pilot and the subsequent forced landing. The investigation focused on the physical evidence recovered from the propeller assembly to confirm the mode of failure.