What happened
During a descent toward Toledo Airport at an altitude of approximately 7,000 feet, a critical mechanical failure occurred on the right engine of the aircraft. All four propeller blades on the right side detached from the hub at the same time. During this event, one specific blade struck the fuselage, leading to an immediate loss of cabin pressure. Following the separation of the blades, the pilot was unable to maintain control of the aircraft. The plane entered a steep dive and impacted an open field situated two miles southeast of Marseellles, Ohio. The impact resulted in the total destruction of the airframe and 38 fatalities, with no survivors among the occupants.
Findings
Investigation into the accident identified that the primary cause was a manufacturing defect involving the right propeller. Specifically, a torque piston for the third blade had not undergone the required nitriding process, which is necessary for surface hardening the helical splines. This omission led to several cascading failures:
- The unhardened torque piston failed due to fatigue from excessive loads on the torque cylinder.
- This failure caused a drop in oil pressure within the propeller assembly.
- The resulting decrease in propeller pitch occurred faster than the pitch lock mechanism could compensate for.
- The engine entered an overspeed condition, creating enough stress to force the blades to separate from the hub.
Furthermore, the investigation noted that the manufacturing quality control system failed to identify the missing nitriding step. This error was linked to a breakdown in production accountability when certain parts were moved between the production line and the laboratory. Additionally, existing oil contamination checks were found to be ineffective at detecting the defective components.