On June 7, 2014, about 1315 Alaska daylight time, a tailwheel-equipped Cessna 180H airplane, N91399, sustained substantial damage while landing at the Wasilla Airport, Wasilla, Alaska. The airplane was being operated by the pilot as a visual flight rules (VFR) flight under the provisions of Title 14, CFR Part 91, when the accident occurred. The certificated private pilot was not injured. Visual meteorological conditions prevailed, and no flight plan had been filed. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on June 7, the pilot stated that the airplane's main landing gear wheels were not tracking true on his last flight, and exhibited a left turning tendency on the ground. The airplane had recently undergone maintenance, and the main landing gear had been realigned before the accident flight. The pilot reported that on his third landing, upon touchdown, the airplane turned sharply to the left. He attempted a go-around, but the airplane continued to veer to the left, off the runway surface, exited the runway safety area, and impacted the upslope of a drainage ditch. The left main landing gear separated from the fuselage, and the airplane sustained substantial damage to the gear box, left wing, ailerons, left horizontal stabilizer and left elevator. A postaccident examination of the airplane by the NTSB IIC and another NTSB investigator revealed that the main landing gear shim bolts were in place, but the main landing gear attachment bolt had broken. The bolts fractured surfaces and surrounding area revealed fracture features and deformation patterns consistent with a ductile overstress fracture. The examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. The closest weather reporting facility is Wasilla Airport. At 1316, an aviation routine weather report (METAR) at Wasilla, Alaska, reported: wind, calm; visibility, 10 statute miles; few clouds at 7,500 feet; overcast clouds at 8,500 feet; temperature, 59 degrees F; dew point 37 degrees F; altimeter, 29.69 inHG.