What happened
While performing a visual approach for landing, the aircraft experienced an engine failure. In response to the loss of power, the pilot initiated an emergency landing. During the subsequent emergency descent, the pilot did not maintain an airspeed above the aircraft's stall speed. As a result, the aircraft entered a stall and impacted the ground in rough terrain. The pilot was not injured.
The investigation
Post-accident examination of the power plant revealed that the flyweights of the left magneto impulse coupling had struck the stop pins. This impact between the flyweight and the stop pin caused the magneto to seize and sheared the accessory drive gear alignment dowel. This mechanical failure led to the uncoupling of the accessory drive train, which ultimately caused the engine to fail.