On June 12, 1999, at 1200 mountain daylight time, a Butler SX-300 homebuilt experimental aircraft, N120J, sustained substantial damage when the left main landing gear collapsed during taxi from landing at Hill AFB, Ogden, Utah. The commercial pilot and sole occupant was not injured. Visual meteorological conditions prevailed for this air show flight operating under Title 14 CFR Part 91 and no flight plan was filed. The flight departed Salt Lake City, Utah, earlier in the day. The pilot said he was taxiing the aircraft to the ramp following landing and the left main landing gear collapsed when he made a turn. According to the Federal Aviation Administration (FAA) Inspector who examined the aircraft following the accident, the pilot had landing gear problems a few days before the accident. The pilot related to the FAA inspector that he had heard a loud "bang/thump" from the landing gear but could not find the origin. In a post-accident examination, the FAA inspector examined the left landing gear and determined the strut's outer trunnion flange had cracked and broke free from its attachment bolt. The inspector said this action allowed the strut to rotate forward. With this rotation, the actuator ram threaded rod end bent, then snapped free from the self-aligning anti-friction rod end assembly. The strut continued forward and impacted the fuselage causing damage to a structural bulkhead. Both sides of the empennage sustained damage and exhibited wrinkled skin panels.