NTSB Identification: MIA99FA252.
The docket is stored in the Docket Management System (DMS). Please contact Records Management Division
Scheduled 14 CFR operation of CONTINENTAL AIRLINES (D.B.A. operation of CONTINENTAL AIRLINES )
Accident occurred Sunday, September 12, 1999 in WEST PALM BEACH, FL
Probable Cause Approval Date: 08/03/2000
Aircraft: Boeing B737-300, registration: N17356
Injuries: 89 Uninjured.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

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.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The fatigue fracture and separation of the high pressure turbine forward rotating air seal due to a manufacturing defect in a bolt hole that was not detected by the engine manufacturer due to inadequate and ineffective inspection techniques. Contributing to the accident was the engine manufacturers failure to provide adequate hole making requirements at the time the forward rotating air seal was manufactured and the engine manufacturers failure at the time of last inspection to require eddy current inspections for the high pressure turbine forward rotating air seal bolt holes.

Full narrative available

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