What happened
While performing a landing on a gravel airstrip, the pilot engaged the propellers into reverse thrust. During this maneuver, the airplane began to veer toward the left side of the runway. In an attempt to maintain directional control, the pilot applied the right brake and continued to increase reverse thrust on the right engine. Despite these efforts, the pilot was unable to control the aircraft, resulting in the airplane departing the left side of the airstrip and encountering brush and rough terrain. The occupants were not injured.
The investigation
Mechanical examination of the engines focused on the propeller control units. Investigators discovered that a pin within the right engine's propeller control unit had separated. This specific pin serves as the component on which the propeller control cam slides, and the cockpit propeller control operates this cam directly. Upon examining the fracture surface of the failed pin, investigators determined that the pin failed in overload.