On May 25, 2023, about 1245 Pacific daylight time, a Cessna 310I airplane, N6PK, was substantially damaged when it was involved in an accident near Sunnyside, Washington. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that the final approach for landing was normal and after the gear handle was lowered he got a green light signifying that the gear was down. The landing was “firm” and, shortly after touchdown, the airplane’s right main landing gear slowly collapsed, causing the right wing to drop. Subsequently, the airplane veered to the right and exited the runway. The airplane came to rest in a field adjacent to the runway, about 100 ft from the runway centerline. During the accident sequence, the airplane sustained substantial damage to the right horizontal stabilizer and elevator. Postaccident examination of the right main landing gear revealed that the side brace lock assembly of the left main landing gear had separated. The lock assembly was sent to the National Transportation Safety Board Material’s laboratory for examination. Examination revealed that the forward lug of the clevis at the lower end of the bellcrank was fractured and the other lug remained intact. The mating side of the fractured lug, the bearings, and pin that attached the side brace lock to the lower end of the bellcrank were not recovered. The fracture surface had a rough matte appearance that was consistent with a ductile overstress fracture. Additionally, a portion of the fracture surface had smearing damage on the aft side that was consistent with sliding contact with the side brace lock link. On the intact lug, the inboard forward portion of the hole was deformed. The attachment bolt at the lower end of the left main landing gear side brace lock assembly was bent downwards. The lock link deformation and the bent bolt attaching the lock link to the side brace were consistent with axial compression loads on the assembly. A brownish black object was observed in the inboard side of the attachment pin hole, consistent with the set screw for the retaining pin that attached the bellcrank to the lock link. The area surrounding the attachment pin hole was deformed with a curved shape consistent with contact with the lower end of the missing bellcrank flange after being displaced downward relative to the lock link (these areas are normally not in contact in an intact assembly).