What happened
During the approach phase of the flight, the flightcrew encountered difficulties extending and locking the right main landing gear. Despite multiple attempts to rectify the situation and consultation with company personnel and standard checklists, the crew proceeded with an emergency landing while the gear remained in an unsafe configuration. Upon touchdown, the right main landing gear underwent a slow collapse, causing the aircraft type to come to a stop off the right side of the runway.
Findings
Post-accident inspections of the right main landing gear assembly identified significant damage to the hardware used to secure the retract actuator fitting. The assembly utilized two fasteners: a larger bolt and a smaller bolt. Investigators discovered that the nut and cotter key for the smaller bolt were missing. Furthermore, eight of the twelve threads on the smaller bolt were found to be stripped, a condition consistent with the nut being pulled away from the bolt due to overstress.
The larger bolt was also found to be bent and had separated near its head. This failure was consistent with tension and overstress resulting from the initial failure of the smaller bolt. These mechanical failures were consistent with the right main landing gear failing to remain locked in the extended position once the weight of the aircraft was applied. Notably, an examination of the down lock system did not reveal any mechanical malfunctions prior to the impact, and a subsequent tomography scan and functional test of the retract actuator at the manufacturer's facility, overseen by an FAA inspector, showed no anomalies.