Incident Overview
A takeoff run on the Kahiltna Glacier was interrupted when the left wheel ski pivot shaft fractured and failed. The failure caused the right wing to drag on the snow surface.
Examination Findings
Post-incident examination of the fractured pivot shaft revealed several deviations from the manufacturer's blueprints. The shaft was constructed from 4300 series steel. The two keyways on the shaft were machined differently from one another. Additionally, the radius on the circumferential step of the shaft was irregular.
Specification Non-Compliance
The observed conditions in the keyways and the step radius did not conform to the specifications set forth in the manufacturer's blueprints. The exact nature of the discrepancy included inconsistent machining and an irregular radius profile.
Conclusion
The incident resulted from the fracture of the left wheel ski pivot shaft during a takeoff run on the Kahiltna Glacier. The shaft exhibited manufacturing deviations that did not align with the prescribed design specifications.