Accident Details
On May 25, 2023, at about 1245 Pacific daylight time, a Cessna 310I airplane, N6PK, was substantially damaged during a landing accident near Sunnyside, Washington. The pilot and passenger were not injured. The flight was operated as a personal flight under Title 14 Code of Federal Regulations Part 91.
The pilot reported that the final approach was normal. After lowering the landing gear handle, a green light indicated the gear was down. The landing was described as "firm." Shortly after touchdown, the right main landing gear slowly collapsed, causing the right wing to drop. The airplane veered right and exited the runway, coming to rest in an adjacent field about 100 feet from the runway centerline. The accident sequence resulted in substantial damage to the right horizontal stabilizer and elevator.
Postaccident Examination
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 Materials Laboratory for examination.
Examination showed that the forward lug of the clevis at the lower end of the bellcrank was fractured, while the other lug remained intact. The mating side of the fractured lug, along with 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 consistent with a ductile overstress fracture. A portion of the fracture surface exhibited smearing damage on the aft side, 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 downward. The lock link deformation and the bent bolt 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.