WPR23LA096

The pilot receiving instruction was conducting takeoffs and landings to regain tailwheel currency. During the second landing’s roll out, the airplane began to veer left of the runway centerline. The pilot applied correction with right rudder; however, he overcorrected and the airplane veered to the right. The pilot and the flight instructor both applied left rudder and brake to counteract the veer to the right. However, the veer to the right developed into a ground loop and the left main landing gear leg fractured. The airplane dropped onto the fractured end of the landing gear leg and came to rest upright. A metallurgical examination of the fractured landing gear leg revealed small fatigue cracks along the radius of the brake line retainer clip bore and outboard face. These small fatigue cracks concentrated stress in the radius, facilitating a premature overstress fracture due to the stresses on the part during the landing.

On January 23, 2023, about 1630 mountain standard time, a Cessna 170A, N9534A, sustained substantial damage when it was involved in an accident near Mesa, Arizona. The pilot, flight instructor, and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. According to the pilot receiving instruction, he was conducting takeoffs and landings to regain tailwheel currency. During the landing roll after the second landing, the airplane began to veer to the left. He applied correction with right rudder; however, he overcorrected and the airplane veered to the right. The pilot receiving instruction and the flight instructor both applied left rudder and brake to counteract the veer to the right. Despite their corrections, the airplane ground looped to the right. During the ground loop, the left main landing gear leg fractured mid span, near the brake line retainer clip bore, and the left wing contacted the runway surface. Postaccident examination and fracture analysis of the left main landing gear leg was conducted by the National Transportation Safety Board Materials Laboratory. The examination revealed that the landing gear failed in its final landing due to small fatigue cracks present along the radius of the retainer clip bore and the outboard face. Outside the fatigue cracks, the fracture surface exhibited features consistent with overstress fracture. The fatigue cracks initiated at small corrosion pits along the radius of the bore, and propagated until the final landing, when the remainder of the leg fractured from overstress.