On June 18, 2002, approximately 1950 Pacific daylight time, a Cessna 441, N564AC, experienced a right main gear collapse during the landing roll at Rogue Valley International Airport, Medford, Oregon. The aircraft was being operated by Erickson Air-Crane. The airline transport pilot, and his three passengers were not injured, but the aircraft sustained substantial damage. The 14 CFR Part 91 business flight, departed Lake Tahoe Airport, South Lake Tahoe, California, approximately one hour and thirty minutes prior to the accident, and was being operated in visual meteorological conditions. An instrument flight plan had been filed and activated. The ELT was not activated. According to the pilot, after takeoff the gear retraction did not feel normal, and it appeared as though the gear cycle did not end. Because the pilot suspected gear failure, he initiated the emergency checklist and retracted the flaps. At that point, because all indications were normal, the pilot had a passenger visually check the position of the main gear. At that time it was discovered that the right main gear had not retracted. The pilot then re-cycled the gear twice and noted that both the gear transition light and the hydraulic flow light failed to extinguish at the end of the cycle. The pilot then deactivated the landing gear system in order to prevent porting of hydraulic fluid. Following that action, the pilot activated the flaps in order to insure flap control for landing and to insure that there was still fluid in the system. After making the determination that the hydraulic system was still operable, the pilot made the decision to continue on to Medford, which is the home base for the aircraft. While en route, the left main gear and the nose gear remained retracted, but the right main gear remained in a partially extended position. Prior to landing at Medford, the pilot lowered the gear and insured that all of the landing gear green (down and locked) lights were illuminated, and that the gear in-transit light was extinguished. In addition, he had one of the passengers confirm that both of the main gear appeared to be in the full-down position. That passenger noted that although both gear appeared fully down, the right main gear appeared to be hanging lower than the left. The pilot then moved the passengers to the left side of the aircraft, and attempted to touch down primarily on the left main gear and the nose gear. Although the touchdown and initial part of the landing roll were uneventful, as the aircraft decelerated to about 55 knots, the right main gear slowly collapsed. A post-accident inspection of the right main gear determined that the roll pin that held the forward gear pivot pin in its slot in the gear trunnion had fractured (see attached diagram). According to Cessna Aircraft, the failure of the roll pin allowed the pivot pin to work its way loose over time, ultimately resulting in a misaligned gear trunnion that jammed during the retract cycle. The jamming during the attempted retraction exacerbated the misalignment, and that along with the looseness of the pivot pin, created a situation where a low load force could cause the gear to collapse during the landing roll. A portion of the subject roll pin was submitted to the NTSB laboratory for metallurgical inspection. That inspection revealed that there was no evidence of fatigue along the fracture surface, and that the fracture features were consistent with overstress. The investigation revealed no evidence of unusual wear or damage in the area of the pivot pin or its phenolic bearing, nor was there a record of any recent event that would have exposed the gear pivot mechanism to an overload situation.