On June 8, 2005, at 2137 eastern daylight time, a Saab 340A, N40SZ, operated by Shuttle America Corp. as United Express flight 7564, sustained minor damage during an emergency landing at Washington Dulles International Airport (IAD), Dulles, Virginia. There were no injuries to the 3 crewmembers and 27 passengers. Visual meteorological conditions prevailed for the flight that originated from Westchester County Airport (HPN), White Plains, New York. An instrument flight rules flight plan was filed for the air carrier flight conducted under 14 CFR Part 121. According to the captain, the airplane was approaching IAD when the flightcrew attempted to extend the landing gear. A yellow transit light cockpit indication was observed, which alerted the flightcrew that the right main landing gear had not fully extended and locked. After "recycling" the landing gear, the flightcrew noted the same anomaly. The flightcrew advised air traffic control (ATC) of the problem, performed a missed approach, and climbed to 3,000 feet over the airport. While circling the airport, the flightcrew performed all relevant checklists in the quick reference handbook (QRH); however, they could not correct the anomaly. In addition, the flightcrew performed a low pass over the airport. Ground personnel observed the gear extended, but could not confirm that it was locked in the fully extended position. The flightcrew also contacted their company twice to discuss the problem. The decision was made to perform an emergency landing with the unsafe landing gear indication. After completing the emergency checklist items in the QRH, the flightcrew performed an emergency landing on runway 19L. During the landing, the right main landing gear slowly collapsed, and the airplane came to rest in a grassy area off the right side of the runway. An emergency evacuation of the airplane was performed successfully, and no serious injuries were reported. The airplane was equipped with a cockpit voice recorder (CVR) and flight data recorder (FDR), which were forwarded to the Safety Board's vehicle recorders laboratory for readout. Data on the recorders confirmed the captain's statement. Components of the right main landing gear were examined at the Safety Board's materials laboratory. The right main landing gear retract actuator fitting was secured with two fasteners, a smaller bolt (part number AIR 134736) and a larger bolt (part number AIR 124792). The nut and cotter key were not recovered with the smaller bolt, and 8 of the 12 threads on the smaller bolt were stripped consistent with an overstress pulling of the nut away from the bolt. The larger bolt was bent and separated near the head, consistent with a tension and overstress separation as a result of the smaller bolt failure. The overstress failures were consistent with the right main landing gear not locked in the extended position while aircraft weight was applied to it; however, examination of the right main landing gear down lock system could not determine any pre-impact mechanical malfunctions. Further, the right main landing gear retract actuator was subjected to x-ray computed tomography (CT) and digital scanning under the direction of the Safety Board. The CT scan did not reveal any anomalies with the actuator. The unit was then functionally tested at the manufacturer's facility, under the supervision of an FAA inspector. The unit tested successfully, with no anomalies noted. The airplane was maintained under a continuous airworthiness maintenance program, and had accumulated about 164 hours of operation since its last inspection, which was performed on April 30, 2005.