Incident Overview
During the takeoff roll, as the aircraft lifted off the runway, the pilot heard an unusual sound originating from behind the passenger seat. Shortly after, a radio call from another aircraft informed the pilot that the left landing gear appeared abnormal. Unable to visually inspect the left landing gear leg from his seat, the pilot performed a low, slow pass over an observer stationed on the ground. The observer relayed via radio that the left landing gear was "detached from the strut and dangling from the center of the fuselage."
Precautionary Landing and Ground Loop
After receiving the observer's report, the pilot circled the aircraft and initiated a precautionary landing. During touchdown, the aircraft momentarily contacted the runway on only the right main wheel and tail wheel. Subsequently, the left wing lowered and made contact with the runway surface. The pilot lost directional control, and the aircraft ground looped to the left before coming to rest in an upright position.
Post-Accident Inspection
Following the incident, one of the aircraft owners conducted a post-accident inspection. The examination revealed that the left landing gear lock nut was missing a lock nut set screw. According to the owner, without the set screw, it is possible that the lock nut could have unthreaded, allowing the cylinder assembly to separate from the axle strut assembly.