On September 27, 2000, at 0959 mountain daylight time, a Piper PA-31-350, N159SW, operated by Western Aviators Inc., was substantially damaged during a gear up landing at Walker Field, Grand Junction, Colorado. The commercial pilot, the sole occupant aboard, was not injured. Visual meteorological conditions prevailed, and a visual flight rules flight plan had been filed for the cargo flight being conducted under Title 14 CFR Part 135. The flight originated at Rifle, Colorado, at approximately 0905. According to the pilot's accident report, the cargo flight originated from Jefferson County Airport, Broomfield, Colorado, and the flight to Rifle was uneventful. As he made his landing approach to Walker Field in Grand Junction, the right main landing gear failed to extend and lock. A low pass was made and tower personnel confirmed that the landing gear was not extended. The pilot followed emergency procedures in an attempt to extend the landing gear, but to no avail. He made an intentional gear up landing on runway 04 as emergency equipment stood by. Postaccident examination disclosed that the right forward inboard landing gear door hinge pin (p/n 46652-2) had broken, preventing the landing gear from extending. Although the pilot reported only minor damage to the airplane, insurance repair estimates indicate substantial damage had been incurred since several bulkheads and formers had to be replaced.