Incident Summary
During climb after takeoff, the flight experienced an uncontained failure of the No. 1 engine. The flight returned to the departure airport and landed without further incident.
Damage and Debris
Examination of the airplane showed damage to the left wing high lift devices, fuselage, vertical and horizontal stabilizers, rudder, and tail cone. The No. 1 engine left thrust reverser had separated. Debris from the No. 1 engine was located over an area spanning eight blocks long by three blocks wide in the city below.
Engine Examination
Examination of the No. 1 engine revealed a 360-degree separation in plane with the high pressure turbine (HPT) rotor. The HPT shaft and the HPT forward rotating air seal had exited the engine. The HPT rotating air seal was recovered in the debris field.
Metallurgical Findings
Metallurgical examination showed the rotating air seal had two radial fractures that passed through the bore and the HPT front shaft-to-HPT disk attachment bolt holes. Fatigue cracking was identified in one attachment bolt hole. The fatigue crack initiated from a heat affected layer, which was caused by abusive machining during the manufacturing process due to loss of coolant during the drilling process. Based on striation count, the fatigue crack was at detectable length during two in-service inspections, but was not detected.