On April 4, 2007, about 1800 Pacific daylight time, a Champion 7ECA airplane, N6096F, sustained substantial damage during takeoff at Pangborn Memorial Airport, Wenatchee, Washington. The airplane was being operated as a visual flight rules (VFR) local area flight under Title 14 CFR Part 91 when the accident occurred. The pilot/registered owner was not injured. Visual meteorological conditions prevailed. No flight plan was filed. The flight originated at Pangborn about 1750. The pilot reported that as the aircraft lifted off of the runway, he heard a "sound" from behind the passenger seat. The pilot received a radio call from another aircraft informing him that the "left landing gear did not look right." The pilot could not see the left landing gear leg from his seat, so he made a low, slow pass over an observer on the ground, who informed him via radio that the landing gear was "detached from the strut and dangling from the center of the fuselage." The pilot circled around and made a precautionary landing. The aircraft momentarily touched down on just the right main wheel and tail wheel, and then the left wing lowered and contacted the runway. The pilot was unable to maintain directional control, and the aircraft ground looped to the left, coming to a rest in an upright position. Post-accident inspection of the aircraft by one of the owners 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, which would have allowed the cylinder assembly to separate from the axle strut assembly.