Incident Summary
During the approach, the flightcrew experienced difficulty in extending and locking the right main landing gear. Multiple attempts were made, and the crew consulted the checklist and company personnel. Subsequently, an emergency landing was carried out despite the unsafe landing gear indication. Upon touchdown, the right main landing gear slowly collapsed, causing the airplane to veer off and come to rest off the right side of the runway.
Examination of the Landing Gear
Post-incident examination of the right main landing gear revealed that the retract actuator fitting was secured with two fasteners: a smaller bolt and a larger bolt. The nut and cotter key associated with the smaller bolt were not recovered, and 8 of the 12 threads on that bolt were stripped, consistent with overstress pulling of the nut away from the bolt. The larger bolt was bent and separated near the head, consistent with tension and overstress separation resulting from the failure of the smaller bolt.
System Testing
The overstress failures were consistent with the right main landing gear not being locked in the extended position when aircraft weight was applied. However, examination of the right main landing gear down lock system could not identify any pre-impact mechanical malfunctions. Additionally, the right main landing gear retract actuator was subjected to tomography scanning, which found no anomalies. The unit was then functionally tested at the manufacturer's facility under the supervision of an FAA inspector, and it performed successfully with no anomalies noted.
Probable Cause
The official probable cause was stated as: Failure of the right main landing gear to extend and lock for undetermined reasons, which resulted in the right main landing gear collapsing during touchdown.