What happened
Shortly after takeoff, the pilot reported hearing a muffled explosion accompanied by a moderate left yaw and a noticeable deterioration in readings on the number one engine. Despite the mechanical anomaly, the aircraft was able to return to the airport for an uneventful landing.
The investigation
A post-accident examination of the affected powerplant revealed that the failure originated in the third-stage disk and blades area. A detailed metallurgical analysis confirmed that the third-stage turbine blade had suffered a fatigue failure. The examination determined that this failure was most likely induced by rubbing between the turbine shroud and the outer air seal.
Findings
The primary contributing factor to the incident was the fatigue failure of the third-stage turbine blade. This mechanical breakdown was caused by contact between the turbine shroud and the outer air seal, leading to the sudden loss of engine performance during the critical climb phase.