Failure Analysis to Directional Control Pedal Assemblies of a Crashed Helicopter

In investigation to a helicopter crash accident, a pedal for pilot’s yaw control input was found to be separated from pedal pivot arm by fracture through two fillet welds. Fractographic and metallurgical studies were carried out on these two welds. Fatigue striations on the fracture surfaces of the welds were found and the failure was determined to be result of fatigue of the two welds. Furthermore, weld defects including insufficient weld leg, incomplete fusion, overlap on the base metal and porosity were found and evaluated against applicable standards. It was concluded that the welds were not in compliance with the standards and are root cause of the fatigue fracture. Recommendations of revising manufacturer’s production specification and/or redesigning the assembly were made.