Incident Details
On January 23, 2023, at about 1630 mountain standard time, a Cessna 170A, registration N9534A, sustained substantial damage during a landing accident near Mesa, Arizona. The aircraft was operating as a Title 14 Code of Federal Regulations Part 91 instructional flight. The pilot receiving instruction, a flight instructor, and a passenger were not injured.
Accident Sequence
According to the pilot receiving instruction, he was performing 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 right rudder to correct, but overcorrected, causing the airplane to veer to the right. Both the pilot receiving instruction and the flight instructor then applied left rudder and brake to counteract the veer. Despite their efforts, 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
The National Transportation Safety Board Materials Laboratory conducted a postaccident examination and fracture analysis of the left main landing gear leg. The examination revealed that the landing gear failed during the 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 had 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.