19990912041969A

(-23) #1 Engine sustained an un-contained failure due to 7th stage turbine disk air seal (high pressure) that is attached to 7th stage disk. Shaft sheared and dispersed engine fragments 8X3 over city block, NTSB had engine removed and sent to houston for further investigation. (.4)during climb after takeoff, the flight had an uncontained failure of the no. 1 engine. The flight returned to the departure airport and landed without further incident. Examination of the airplane showed there was 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 eight block long by three block wide city block area. Examination of the no. 1 engine revealed that it had a 360 degree separation in plane with the high pressure turbine (hpt) rotor and that 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 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 which initiated from a heat affected layer. The heat affected layer 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.