Cessna 421C N513FS accident near Sterling, Colorado

Probable cause

Failure and separation of the upper and lower right main gear torque links links, which resulted in a loss of directional control on landing roll-out.

NTSB analysis

During the landing roll-out, the airline transport pilot said a 50-knot gust of wind hit the twin-engine airplane from the right side. The airplane weathervaned into the wind, at which time he applied full left rudder to compensate. The pilot tried to maintain control of the airplane as it skipped off the right side of the runway onto the grass. Subsequently, the left main gear collapsed due to the side load and the airplane came to an immediate stop. Examination of the airplane revealed that the nose gear had collapsed, the left main gear had separated from the airframe; the right main landing gear remained attached to the airframe, but the upper and lower torque links had separated, and the wheel was rotated to the right. Further examination of the upper and lower link assemblies securing bolt, bushing, two AN washers, castellated nut, and cotter pin, revealed it had pulled through the lower torque link boss, which allowed the main wheel, brake, and strut assembly to rotate inside the strut housing. In addition, both propellers were damaged and the left wing sustained substantial damage. The airplane was last inspected on March 13, 2008, at which time, the main gear camber and toe was adjusted. The failure occurred approximately 39.1 hours after this last inspection. On November 23, 1983, Cessna issued Service Kit SK 421-118, which called for the replacement of washers and for inspection of the main gear torque links. The Service Kit specified washer P/N 504518-2 to be installed under the bolt head and nut, with replacement washer P/N S1450-5H12-063 to be incorporated into the next revision to the Service Kit. Cessna issued a Service Information Letter in conjunction with the Service Kit for the purpose of "improved service life and main gear alignment retention." The washers listed in the Service Kit were not installed on the accident airplane. Compliance with the Service Kit and Service Information Letter is not mandatory.

Text from the NTSB. Open the NTSB docket for DFW08LA115 for the full record.