Incident Description
During descent from 7,000 to 5,000 feet, the pilot heard a loud bang, accompanied by a temporary vibration and a violent swerve to the right. Looking out the right window, the pilot saw only the tops of the engine mounts and believed the right engine had fallen off. The aircraft could be controlled only after reducing the left engine power to idle.
Forced Landing and Aftermath
The pilot executed a wheels-up forced landing. During the landing, the aircraft tore through a fence, slid across a paved road, and went over an embankment before coming to rest and catching fire. The pilot sustained a back injury and had difficulty exiting the aircraft.
Investigation Findings
Examination revealed that the propeller hub had failed due to fatigue, resulting in blade separation and subsequent engine tearaway. The engine remained attached to the airframe by cables. Metallurgical analysis of the hub showed that the fatigue crack originated at a threaded grease fitting. Gouging was visible on the inner wall of the hub.
Additionally, a set of incorrect counterweights was found on the propeller. The counterweights are designed to reduce vibration.