Review of NTSB Investigations of Cessna 210 Hydraulic Actuator Fractures from Fatigue

Abstract The article reviews National Transportation Safety Board (NTSB) investigations into multiple Cessna 210 aircraft accidents caused by failed hydraulic actuators in the main landing gear systems. Investigators discovered a pattern of fatigue cracks in 7075-T6 aluminum actuator barrels that initiated at corrosion pits along the retaining ring groove, propagated under cyclic loading, and eventually resulted in circumferential and longitudinal fractures that leaked hydraulic fluid. Although these failures have not yet caused significant injuries, they present serious safety risks by impairing pilots' ability to fully extend and lock the landing gear. The article details the metallurgical examinations that revealed multiple crack initiation sites containing chlorine-rich aluminum oxide pits, some with cadmium remnants from the adjacent steel retainer ring, suggesting potential corrosion mechanisms. The researchers conclude that the combination of thin-walled design, stress concentrations at the retaining ring groove, susceptibility of the high-strength aluminum alloy to corrosion, and possibly inadequate inspection procedures all contributed to these premature failures, prompting ongoing work with the FAA to address the issue.