What happened
The left main landing gear collapsed moments after the aircraft touched down on the runway. Weather conditions at the time included winds from 350 degrees at 19 knots, gusting to 29 knots. The captain and copilot reported that the touchdown itself felt normal. However, three flight attendants stated that the aircraft landed hard and began shaking violently. They also noted that the previous two landings had caused significant vibration and shaking within the aircraft.
The investigation
Examination of the landing gear revealed that the left main landing gear tee bolt was separated. A metallurgical analysis of the failed component showed that the fracture originated from a shallow preexisting crack located in the drag brace bearing surface radius. The metallurgist determined this radius was sharper than desired, which likely contributed to the stress concentration and subsequent failure.
Findings
The collapse of the landing gear is directly related to the fractured tee bolt. While the board could not determine if other events or circumstances contributed to the initial failure of the bolt, the operator has since amended their repair specifications for these components to address the issue.