On August 20, 2003, approximately 1230 mountain daylight time, a Piper PA-28-200R, N4816T, registered to and being flown by a private pilot, sustained substantial damage during a gear collapse on landing roll at Nampa, Idaho. The pilot was uninjured. Visual meteorological conditions existed and no flight plan had been filed. The flight, which was personal, was operated under 14CFR91, and originated from Kemmerer, Wyoming, approximately 0950 on the morning of the accident. The pilot reported that prior to executing an approach and landing to runway 29, he verified that he had a three green indication for the landing gear being down and locked. While rolling out on the 5,000 foot long asphalt runway and having decelerated to about 10 miles per hour, the right main landing gear began to collapse. As the aircraft departed the right side of the runway it impacted a runway light. The nose gear collapsed and the propeller struck the ground. An airframe and powerplant mechanic removed the aircraft from the accident site to the facility of Skyline Aircraft Maintenance, Nampa, Idaho. The mechanic reported that a retraction test was accomplished to the aircraft's gear system. The aircraft's landing gear was cycled using an electric power pack and Piper's automatic free-fall system. During the retraction tests, the aircraft's landing gear down-locks and micro switches were found set within manufacturer's limits. The mechanic further stated that in his opinion, "all areas of the landing gear system were in an airworthy condition and functioning properly."