Accident Sequence
The right main landing gear collapsed during the landing roll. The pilot had placed the landing gear in the down position on downwind and noted three green lights, indicating the gear was down and locked. Noting a left crosswind, the pilot landed on the left main landing gear first, then the right main landing gear. When the right main landing gear touched the ground, it folded up, and the airplane departed the runway. The airplane went over a berm, which sheared off the left main landing gear and the nose landing gear. The passengers safely deplaned.
A pilot in another company airplane, about 1 mile behind and 1,000 feet above the accident airplane, observed the landing and indicated that the approach and landing appeared normal. According to the Federal Aviation Administration inspector who inspected the accident scene, the airplane touched down near the threshold. There were two propeller strikes on the runway about 15 inches apart about 40 feet past the touchdown point. About 200 feet farther down the runway, there were multiple propeller strikes. The area between the first set of propeller strikes and the second set was clear of any marks. The inspector observed skid marks that began at the second set of propeller strikes and continued down the runway where the airplane departed the runway.
Post-Accident Examination
The airplane had flown 2 hours since a routine maintenance inspection that included many components of the landing gear system. No discrepancies were noted on the failed components of the right main landing gear. Post-accident inspection by the operator's maintenance personnel found 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 bell crank were fractured. They stated that this led to other parts shifting and breaking, which led to the right main landing gear collapsing.
Metallurgical Findings
Metallurgical examination of the bell crank, the clevis ears, and the bolt determined that all of the materials examined were within specification. None of the fractures showed any evidence of pre-existing damage or fatigue cracking. The bolt fractured in shear overstress on a plane flush with the edge of the bellcrank. The damage to the pivot bolt appeared to be most consistent with an event where the gear was heavily loaded outward, away from its normal retracted position. Detailed analysis of the loadings on the failed components and the lack of damage on the surrounding structures and landing gear parts revealed no obvious scenario that would have led to the bellcrank being the first component loaded sufficiently to cause the damage observed and/or initiate the collapse of the landing gear. It is most likely that the damage to the bellcrank was a result of the collapse of the gear, rather than a cause.