On March 27, 2022, about 1130 central daylight time, a Cessna 172, N8431U, was substantially damaged when it was involved in an accident near Sparta, Tennessee. The student pilot and flight instructor were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight.   According to the instructor, the student pilot was practicing touch-and-go landings. They heard a “pop” sound as the airplane touched down. The student pilot initiated a go-around and then informed the instructor that the left main landing gear (LMLG) had separated from the airplane. They flew for about 2.5 hours to reduce the airplane’s fuel load before attempting to land with the fractured LMLG. The landing was uneventful, and the airplane came to a stop on the runway. According to the instructor, the LMLG struck the horizontal stabilizer when it separated, resulting in substantial damage.

The LMLG spring strut was examined by the National Transportation Safety Board Materials Laboratory. The LMLG spring strut fractured where the step bracket was affixed to the spring strut. The step bracket was tack welded to the spring strut. No epoxy adhesive was present on the faying surfaces of the step bracket or spring strut. According to the Cessna service manual, step brackets can only be affixed to the spring strut using an approved epoxy adhesive on abrasively blasted surfaces; welding on the spring strut is not permitted. The Materials Laboratory examination also found a fatigue crack that initiated at a tack weld between the step bracket and the spring strut and propagated to a length of about 0.2 inches. The fatigue crack led to an overstress fracture during the accident flight.