CESSNA A188A

Full Narrative

On September 11, 2022, at 1900 central daylight time, a Cessna A188A, N2122U, sustained substantial damage when it was involved in an accident near Canby, Minnesota. The pilot was uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight.
The pilot stated that, during the landing, the airplane made an immediate turn when the tailwheel touched down. The airplane spun around, the left main landing gear collapsed, and the left wing struck the ground. The airplane sustained substantial damage to the left wing.
The pilot stated that the tailwheel spring cross tube broke when the tailwheel touched down. He said that the tube had a wall thickness of 0.055 inch, and the superseded tube had a wall thickness of 0.125 inch.
The cross tube was examined by the National Transportation Safety Board Materials Laboratory. The tube wall at the location of the right joint was flattened and substantially deformed consistent with ductile overstress deformation of the tube, and the deformation corresponded to the upward displacement of the attach fitting right end relative to the adjacent fuselage lug. The piece of the tube that had been retained within the lug was ovalized, also consistent with overstress deformation associated with the relative displacement.
The tube material was identified as alloy 4130 steel, consistent with the specified material for the part. The tube had an outside diameter of 0.873 inch and a wall thickness of 0.0481 inch. According to an engineering drawing for the tube at the time of airplane manufacture in 1970, the specified tube had a nominal outside diameter of 0.875 inch and a wall thickness of 0.049 inch. Therefore, the outside diameter of the tube was about 0.002 inch smaller than the specified nominal outside diameter of 0.875 inch, and the wall thickness was 0.0009 inch thinner than the specified nominal wall thickness of 0.049 inch for the original tube design. In 1985, the wall thickness of replacement parts (the airplane model was no longer in manufacture in 1985) was changed to 0.120 inch. The measured hardness was consistent with values for the specified material.