What happened
While climbing through flight level 240, the aircraft's number one engine suffered a fan disk separation. This event caused several components to detach from the engine, including the inlet, the fan rotor assembly, the fan containment case, and parts of the thrust reverser. Following the failure, the airplane reversed course and completed a landing without further incident. The aircraft sustained minor damage to the aft portion of the fuselage and the empennage.
The investigation
Post-incident examinations of the remaining aircraft systems revealed no anomalies. Investigators recovered portions of the fan disk for analysis. Examination of the recovered material revealed fatigue striations originating from the aft bore corner of the fan disk. These striations were found to have originated from an area exhibiting characteristics consistent with arc-out damage. This specific damage was a result of improper assembly and marking procedures used during the electrochemical etching process.
Findings
Investigation determined that the manufacturer's quality assurance process failed to detect the arc-out damage. Additionally, the operator did not identify the damage during inspections required by airworthiness directives because the prescribed inspection procedures lacked sufficient detail to detect such arc-out damage. Furthermore, maintenance personnel had not received appropriate training for these specific detection requirements.