On April 26, 2007, about 1120 Alaska daylight time, a Beech D18S airplane, N502CK, sustained substantial damage when the right main landing gear collapsed after landing at the Levelock Airport, Levelock, Alaska. The airplane was being operated by Air Supply Alaska, Kenai, Alaska, as a visual flight rules (VFR) non-scheduled cargo flight under Title 14, CFR Part 135, when the accident occurred. The solo airline transport certificated pilot was not injured. Visual meteorological conditions prevailed, and a VFR flight plan was filed. The flight departed the Kenai Airport, Kenai, about 1025. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on April 27, the pilot said about 200 feet into the landing roll he heard the gear warning horn activate, and saw the gear in-transit light illuminate. He said the right main landing gear collapsed, and the airplane exited the runway. The pilot said the left gear sheared off as it encountered soft terrain on the side of the runway. He said the airplane sustained damage to right wing and the fuselage. The pilot reported that there were known problems with the landing gear prior to the accident. On April 30, the NTSB IIC met with the FAA aviation safety inspector who visited, and photographed the accident site. He said the airplane landed hard on the runway threshold, became airborne again, and touched down about 300 feet down the runway. The runway is gravel, and the inspector provided photographs that showed impact marks from the main landing gear on the runway threshold. The marks were several inches deep, 3-6 feet in length, and had gravel sprayed forward and to each side of the track. The tracks began again about 300 feet down the runway, with the left main landing gear touching first, followed by the right main landing gear, and then the nose wheel. The tracks veered sharply off the right side of the runway, and terminated at the wreckage. The inspector provided a hand-drawn sketch of the marks with approximate distances.