WPR21LA339

The flight instructor of a tailwheel airplane was demonstrating a wheel landing to the pilot receiving instruction. The airplane touched down normally on its main landing gear, and, as the tailwheel touched down, the airplane veered to the right. The flight instructor attempted to correct back to the runway, but the airplane continued off the runway and ground looped to the right. The left wing and horizontal stabilizer sustained substantial damage. Examination of the airplane revealed the tailwheel fitting had separated near the weld gap between the fitting cross tube and the attachment brace. Metallurgical examination of the fracture surfaces identified corrosion pits where the fatigue cracks had initiated. The corrosion pits formed along the outer diameter surface of the tube within the gap against the brace, which created crevice corrosion. As a result of the crevice corrosion, the landing gear failed during the landing rollout, which caused the pilot to lose directional control of the airplane and subsequent ground loop.

On September 8, 2021, about 1130 Pacific daylight time, a Cessna A185F, N185BB, was substantially damaged when it was involved in an accident near Arlington, Washington. The flight instructor, pilot receiving instruction, and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor of the tailwheel airplane reported that, after the pilot receiving instruction performed several landings, he assumed control of the airplane to demonstrate a wheel landing. During the landing roll to runway 16, as the tailwheel touched down, the airplane veered to the right. While attempting to correct with brake and rudder, the airplane exited the right side of the runway and ground looped to the right. The left wing and horizontal stabilizer struck the surface. Postaccident examination of the airplane revealed that the tailwheel fitting spring attachment was partially fractured and rotated about 90° from its normal position. The tailwheel fitting spring attachment was sent to National Transportation Safety Board Materials Laboratory, Washington, DC, for examination. The examination of the fracture surface revealed fatigue cracking that initiated at the fillet weld gap between the fitting cross tube and the attachment brace. The fatigue cracks initiated at corrosion pits that had formed along the outer diameter surface of the tube within the gap against the brace. These characteristics were consistent with crevice corrosion. A review of the airplane’s maintenance records revealed that, about a month prior to the accident flight, the tailwheel fitting spring attachment was removed, and new bushings and washers were replaced. The tailwheel fitting spring was then reinstalled with new hardware. The age of the tailwheel fitting spring attachment could not be determined.