WPR21LA337

During landing, when the nose gear contacted the runway, the airplane immediately veered to the right, exited the runway surface, nosed over, and came to rest inverted. Postaccident examination of the airplane revealed that the nose gear upper torque link had fractured near the shock strut mount and separated from the shock strut, which resulted in a loss of directional control. Metallurgical examination of the fracture surfaces of the upper torque link revealed signatures consistent with a fatigue fracture.

On September 2, 2021, about 1130 Pacific daylight time, a Cessna 172E airplane, N3965S, was substantially damaged when it was involved in an accident near Enterprise, Oregon. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that following a light touchdown on the center of runway 30, the airplane rolled smoothly on its main wheels for a couple of seconds. As the airplane slowed and the nose wheel engaged the ground, the airplane veered to the left, and the nose gear fully collapsed. He pushed the right rudder and applied full brakes to the right wheel. The airplane exited the runway, nosed over, and came to rest inverted. Examination of the airplane by a Federal Aviation Administration inspector revealed that the airplane sustained substantial damage to the fuselage, vertical stabilizer, and rudder. The nose gear upper torque link was separated from the shock strut. A section of the upper torque link remained attached to the shock strut. The two sections of the upper torque link were removed and sent to the National Transportation Safety Board Materials Laboratory for further examination. (See figure 1.) Figure 1. Photo showing the lower and upper torque link. The red arrow points to the fracture. Flat areas were observed at the forward ribs on the fracture surface of the upper torque link. The flat areas emanated from the forward edge of the ribs and extended almost until the transition from the ribs to the web of the upper torque link. The fracture surface of the cleaned upper torque link was examined using a scanning electron microscope. Within the flat areas on the fracture surface transgranular features consistent with fatigue cracking were observed. Outside the flat areas the fracture surface features were consistent with dimpled rupture from overstress. No specific entries pertaining to the nose gear torque links were observed in the airframe logbook.