Incident Overview
Shortly after departure from runway 13L, while climbing through approximately 400 feet above ground level (AGL), the flight crew heard a loud bang. The upper cowling of the right engine separated from the aircraft. Subsequently, the right engine shut down and the right propeller automatically feathered. The flight crew declared an emergency and executed a single-engine landing without further incident.
Examination and Findings
Inspection of the right engine, a CT7-9B turboprop, revealed that the Stage 2 turbine disk was missing. Approximately one third of the disk was recovered inside the right landing light compartment. One end of the disk fragment had progressed through a cooling air hole. Evidence of a fatigue fracture was present, originating from multiple points on the inboard side of the cooling air hole.
Further research identified a layer of deformed microstructure near the origin area of the fatigue crack, accompanied by a zone of increased disk hardness. In related testing, disks were drilled using dull and worn drill bits, which resulted in plastic deformation and elevated hardness on the inner diameter hole surfaces. According to the manufacturer, the presence of deformed microstructure correlates with a zone of reduced fatigue properties.