On August 18, 2017, about 1145 central daylight time, a Piper PA-18-150 airplane, N82912, was substantially damaged while landing at Avenger Field Airport (SWW), Sweetwater, Texas. The commercial pilot and his passenger were not injured. The airplane was registered to and operated by the United States Department of Agriculture (USDA) as a public aircraft.The pilot reported that he chose to land on runway 17 at SWW because the automated weather observing system at the airport indicated the surface wind was 9 knots from the south-southwest. The pilot stated that he intended to make a wheel landing with the flaps fully extended. He stated that he felt a "little bump" shortly after the airplane touched down on the right main landing gear (MLG), and the airplane began to swerve left. The pilot reported that he was unable to regain directional control with full right rudder and right brake inputs. The airplane continued to swerve left and departed the left runway edge where the right MLG collapsed after it entered soft terrain. The airplane came to rest on a north heading. The airplane sustained substantial damage to the right wing, both main wing spars, and the right elevator.
The Federal Aviation Administration inspector who examined the wreckage identified several fractured MLG components, which were subsequently submitted to the National Transportation Safety Board Materials Laboratory for additional examination.
The left-side MLG hydrasorb shock unit was intact with its external shock cord rings wrapped around its tee flanges. The left MLG brace tube was bent and fractured near where it attached to the left hydrasorb shock unit. Adjacent to the fracture surface, the brace tube exhibited local thinning or necking. The tube fracture surface exhibited either a cup-shaped morphology, or a flat orientation angled at about 45° relative to the tube direction. The observed fracture features and tube damage were consistent with tensile overstress. There was no evidence of preexisting cracks or damage to the left MLG brace tube or its associated hydrasorb shock unit.
The right-side MLG brace tube had buckled and was partially fractured about 5.75 inches from the fitting hole. The fracture surface exhibited a general rough texture with a dull luster, which was consistent with tensile overstress. Additionally, the opposite end of the right MLG brace tube had buckled inward toward the partial fracture. The observed brace tube damage was consistent with bending overstress.
The right-side MLG hydrasorb shock unit exhibited a fracture of its internal piston shaft. The piston shaft had bent downward adjacent to the fracture surface. One side of the fracture exhibited a generally flat surface on one half before it transitioned to a 45° shear lip. Additional examination of the fracture with a scanning electron microscope revealed dimple rupture in a slanted orientation. The observed fracture features and damage to the internal piston shaft were consistent with bending overstress. There was no evidence of preexisting cracks or damage to the internal piston shaft. The chemical composition, microstructure, and measured material hardness were consistent with a martensitic precipitation-hardened stainless-steel alloy.