The student was being instructed in crosswind techniques, and several circuits and landings had been completed without incident. On the final circuit a normal approach and touchdown were made, but during the landing roll the right wing lowered and the aircraft swung through 90 degrees. Initial inspection found that the lower torque link bolt on the right gear had failed, allowing the wheel assembly to detach. Engineering investigation revealed that the torque link bolt was of defective manufacture in that stress raisers existed near the thread root. This condition resulted in a slow progressive fatigue fracture originating from the stress raisers. There is no inspection requirement for this bolt and the defect is considered an isolated case.
