Incident Summary
The pilot was conducting a visual descent at night to the destination airport. During the approach, the pilot reduced airspeed and deployed flaps. As the aircraft neared the airport, the pilot increased the flap angle and adjusted the propellers to the landing RPM, causing further airspeed decrease. At that moment, the pilot reported hearing a noise resembling flutter, which they believed originated from the right engine. Despite applying full throttle, the airspeed continued to decrease, prompting the pilot to execute a forced landing on a nearby freeway.
Collision and Post-Crash Examination
Upon touchdown, the aircraft collided with a motor vehicle and slid to a stop. A post-crash examination revealed that the RPM control levers and bellcranks were set to the high RPM position. The left propeller was found in the feathered position, indicating an uncommanded feathering event.
Probable Cause
The official probable cause was determined to be the pilot's failure to detect an uncommanded propeller feathering procedures established in the pilot's operating handbook. Contributing findings included a partial loss of engine power due to a failure of the propeller system/accessories feathering system, the pilot's non-compliance with emergency procedures, and impaired visual/aural perception during the approach phase. The forced landing occurred during the approach in VFR pattern conditions, and the collision with a vehicle took place during the landing flare/touchdown on a dark night on a roadway.