What happened
During the approach phase of the flight, the flightcrew encountered an issue where the right main landing gear failed to extend and lock into position. After making several attempts to resolve the issue while consulting checklists and communicating with company personnel, the crew proceeded with an emergency landing despite the unsafe landing gear indication.
Upon touchdown, the right main landing gear slowly collapsed. The aircraft came to rest off the right side of the runway. There were no injuries reported in the accident.
The investigation
An examination of the right main landing gear focused on the retract actuator fitting, which was secured by two fasteners: a smaller bolt and a larger bolt. Investigators found that the nut and cotter key for the smaller bolt were not recovered. Additionally, 8 of the 12 threads on the smaller bolt were stripped, which was consistent with an overstress event pulling the nut away from the bolt.
The larger bolt was found to be bent and had separated near the head. This failure was also consistent with tension and overstress resulting from the failure of the smaller bolt. While these failures were consistent with the right main landing gear not being locked in the extended position when weight was applied, examination of the down lock system did not reveal any pre-impact mechanical malfunctions.
A tomography scan of the right main landing gear retract actuator showed no anomalies. The unit subsequently underwent functional testing at the manufacturer's facility under the supervision of an FAA inspector, where it tested successfully with no issues noted.