Incident Description
Following takeoff, the pilot observed that the right main landing gear had not retracted. Two attempts to recycle the gear were unsuccessful. The pilot then deactivated the landing gear system to prevent hydraulic fluid porting. Prior to landing, the gear was lowered and all green (down and locked) indicator lights were confirmed illuminated, with the gear in-transit light extinguished. The touchdown and initial landing roll proceeded without incident. However, as the aircraft decelerated to approximately 55 knots, the right main gear slowly collapsed.
Post-Accident Examination
A post-accident inspection of the right main gear assembly revealed that the roll pin securing the forward gear pivot pin within its slot in the gear trunnion had fractured. This fracture allowed the pivot pin to gradually work its way loose over time, leading to a misalignment of the gear trunnion. During the attempted retraction cycle, the misalignment caused the gear to jam. The jamming during retraction further exacerbated the misalignment. This condition, combined with the looseness of the pivot pin, created a scenario where a low load force during the landing roll was sufficient to cause the gear to collapse.
Metallurgical Analysis
The National Transportation Safety Board (NTSB) metallurgical laboratory examined the fractured roll pin. The analysis found no evidence of fatigue on the fracture surface. The fracture features were consistent with overstress. Additionally, there was no indication of unusual wear or damage in the area of the pivot pin or its phenolic bearing. The investigation did not identify any recent event that would have subjected the gear pivot mechanism to an overload situation.
Conclusion
The investigation determined that the collapse of the right main landing gear was caused by a fractured roll pin that allowed the forward gear pivot pin to loosen, resulting in a misaligned gear trunnion. The jamming during the retraction cycle worsened the misalignment, and the subsequent landing roll provided a low load force that led to the gear collapse.