Cessna 170 N9534A accident near Mesa, Arizona

Probable cause

The pilot’s failure to maintain directional control during the landing roll out and the preexisting fatigue cracks in the left main landing gear leg, which resulted in the leg’s premature overstress fracture during the ground loop.

NTSB analysis

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.

Text from the NTSB. Open the NTSB docket for WPR23LA096 for the full record.