ANC03IA037 · Cessna 206

The airline transport certificated pilot was landing a nose wheel-equipped airplane at a remote gravel surfaced airstrip during a VFR air taxi flight. The airplane landed hard, and the right main landing gear, a spring steel strut, fractured and separated from the fuselage just outboard of the landing gear fuselage support clamp. The airplane settled onto the belly-mounted cargo pod and sustained minor damage. The airplane had accrued about 17,120 total flight hours. The right main gear was replaced in 1994, at an aircraft total time of 11,848 hours, with a "serviceable unit." Visual examination of the fracture surface revealed beach marks radiating in successive arc patterns from mulitple locations, along the underside of the gear strut. A metallurgical examination revealed that the landing gear spring had two different layers of paint. Multiple fatigue crack initiation sites, coinciding with corrosion pits, were found along the lower surface of the gear. Particles in the pits contained titanium, a component of paint, indicating the corrosion pits were present at the time the gear was painted. Periodic visual inspection of the landing gear is required by 14 CFR Part 43. Neither the manufacturer nor the FAA have established time in service limits (hours or cycles) for the main landing gear strut. Removal of the gear strut for inspection, or the use of nondestructive inspection techniques is not required by the manufacturer or the FAA. On March 16, 2001, the NTSB recommended that the FAA issue an airworthiness directive (AD) to require an initial and recurring inspection of Cessna main landing gear spring steel struts, using nondestructive inspection techniques. On August 31, 2001, the FAA reported to the NTSB that the current inspection criteria outlined in the Cessna Maintenance Manual are adequate to detect cracks in the main landing gear struts, and that additional airworthiness action is not warranted. On March 25, 2002, the NTSB responded by stating, in part: "The Safety Board continues to believe that a visual inspection alone will not detect cracks in the Cessna main landing gear spring struts. However, the Safety Board acknowledges that the statistical evidence does not warrant issuance of ADs at this time as called for in the Board's recommendation." The safety recommendation was then classified as: "Closed-Reconsidered."

Verbatim NTSB analysis and probable cause from the NTSB dataset