Accident Overview
During a VFR air taxi flight, an airline transport certificated pilot landed a nose wheel-equipped airplane on a remote gravel surfaced airstrip. The landing was hard, causing the right main landing gear—a spring steel strut—to fracture and separate from the fuselage just outboard of the landing gear fuselage support clamp. The airplane then settled onto its belly-mounted cargo pod, which sustained minor damage.
Investigation Findings
A metallurgical examination of the fractured strut revealed that the landing gear spring had two different layers of paint. Multiple fatigue crack initiation sites were found along the lower surface of the gear, coinciding with corrosion pits. Particles in the pits contained titanium, a component of paint, indicating that the corrosion pits were present at the time the gear was painted. Visual examination of the fracture surface showed beach marks radiating in successive arc patterns from multiple locations along the underside of the strut.
The right main landing gear had been replaced in 1994 at an aircraft total time of 11,848 hours with a "serviceable unit." At the time of the accident, the airplane had accrued about 17,120 total flight hours.
Regulatory Context
Periodic visual inspection of the landing gear is required by 14 CFR Part 43. However, neither the manufacturer nor the FAA has 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 initial and recurring inspection of Cessna main landing gear spring steel struts using nondestructive inspection techniques. On August 31, 2001, the FAA responded 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, 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 subsequently classified as "Closed-Reconsidered."