What happened
During the landing roll, the right main landing gear of the aircraft collapsed. Prior to touchdown, the pilot had extended the landing gear on downwind and confirmed three green lights, indicating the gear was down and locked. While a left crosswind was present, the aircraft touched down on the left main gear first, followed by the right main gear.
Upon contact with the ground, the right main landing gear folded upward, causing the aircraft to depart the runway. The aircraft subsequently traveled over a berm, an impact that sheared off both the nose landing gear and the left main landing gear. All passengers were not injured and deplaned safely. An observer in another aircraft trailing the accident plane approximately 1 mile behind and 1,000 feet above reported that the approach and landing appeared normal.
An FAA inspector noted the aircraft touched down near the runway threshold. Evidence at the scene included two propeller strikes on the runway located approximately 40 feet past the touchdown point, followed by multiple propeller strikes roughly 200 feet further down the runway. Skid marks began at the second set of propeller strikes and continued until the aircraft left the runway.
The investigation
The aircraft had been in service for only two hours following a routine maintenance inspection that included various landing gear components, with no discrepancies noted at that time. Post-accident inspections by maintenance personnel revealed that the pivot bolt in the right main landing gear bellcrank assembly (part number NAS 464P4-26) had sheared in two places, and the clevis ears at both ends of the bellcrank were fractured. This failure caused other parts to shift and break, leading to the collapse.
A metallurgical examination of the bolt, bellcrank, and clevis ears determined that all materials were within specification, with no evidence of pre-existing damage or fatigue cracking. The investigation found the bolt fractured due to shear overstress on a plane flush with the edge of the bellcrank. The damage to the pivot bolt was consistent with an event where the gear was heavily loaded outward, away from its normal retracted position.
Detailed analysis of the loads on the failed components and the lack of damage to surrounding structures revealed no obvious scenario where the bellcrank would have been the first component loaded sufficiently to initiate the collapse. It is most likely that the damage to the bellcrank was a result of the gear collapse rather than the cause.