What happened
During a climb phase following departure, the left engine experienced a failure. The crew successfully completed all necessary procedures to secure the engine, allowing the aircraft to land without further incident. There were no injuries reported during the event.
The investigation
Upon inspection of the aircraft, investigators found extensive damage located within the left engine nacelle and the turbine section. Specifically, the first stage low pressure turbine (LPT) rotor disk had separated from the low-pressure turbine shaft. This separation caused the disk to penetrate the inner stage transition liner.
Following the initial inspection, the engine was removed from the aircraft for a full disassembly. This process revealed that the first stage LPT was missing a portion of the web and rim outboard of the curvic coupling.
A metallurgical examination was performed on the ruptured first stage LPT disk. The analysis determined that the failure was caused by high cycle fatigue which originated from a subsurface location. Despite the fracture, the dimensions of the disk near the failure site and the material properties of the disk were found to be in compliance with all engineering specifications.