Accident Overview
During the landing roll, after the nosewheel contacted the runway, the airplane decelerated rapidly, veered uncontrollably to the right, and nosed over. The runway showed a single, wide black skid mark extending from near the centerline to the point where the airplane came to rest inverted.
Pilot Report
The pilot stated that during cruise flight, he noticed the airplane required a greater than normal amount of right rudder input to maintain coordinated flight. The airplane had accumulated 81.4 hours since new.
Aircraft Examination
Examination of the airplane revealed that the upper torque link bolt was fractured, with a separated portion of the bolt lodged in the torque link assembly. The bolt exhibited shear deformation adjacent to the fractures, consistent with shear overstress. The lower torque link bolt and the connecting bolt also showed shear deformation. Microhardness testing of samples taken from the bolts indicated that the material complied with the manufacturer's specifications. Additionally, the forward face of the stop lug on the upper torque link displayed deformation from multiple impacts.
Maintenance History
The pilot reported that the airplane's nose strut had been serviced twice since April 2004 because it visually appeared low. The mechanic who serviced the strut the day before the accident stated he added nitrogen to achieve a strut extension of approximately two and a half inches. He then moved the strut up and down to check for bottoming out, over service, and a return to static extension of approximately two and a half inches. The airplane was flown for two approximate one-hour flights following that service.
A review of the Cessna Aircraft Company Model 172 Maintenance Manual, Page 301, "Nose Landing Gear Shock Strut - Servicing," indicates that Section 2.B.(8) states: "With strut fully extended and nose wheel clear of ground, inflate strut to 45 psi."