NTSB Identification: DCA89MA063.
The docket is stored on NTSB microfiche number 39915.
Scheduled 14 CFR operation of UNITED AIRLINES
Accident occurred Wednesday, July 19, 1989 in SIOUX CITY, IA
Probable Cause Approval Date: 10/08/1992
Aircraft: MCDONNELL DOUGLAS DC-10-10, registration: N1819U
Injuries: 111 Fatal,47 Serious,125 Minor,13 Uninjured.

NTSB investigators traveled in support of this investigation and used data obtained from various sources to prepare this aircraft accident report.

The Safety Board's full report on this investigation is provided as Aviation Accident Report number AAR-90/06. To obtain a copy of this report, or to view the executive summary online, please see the Web site at http://www.ntsb.gov/publictn/publictn.htm


UNITED AIRLINE FLT 232 WAS CRUISING AT FL 370, WHEN THERE WAS A CATASTROPHIC FAILURE OF THE # 2 (TAIL MOUNTED) ENG. THIS WAS DUE TO SEPN, FRAGMENTATION & FORCEFUL DISCHARGE OF THE STAGE 1 FAN ROTOR ASSEMBLY PARTS FM THE #2 ENG (UNCONTAINED FAILURE), WHICH LED TO LOSS OF THE 3 HYD SYSTEMS THAT POWERED THE FLT CTLS. THE FLIGHTCREW EXPERIENCED SEVERE DIFFICULTIES CTLG THE ACFT, WHICH SUBSEQUENTLY CRASHED DRG AN EMERG LNDG AT SIOUX CITY. AN INV REVEALED EVIDENCE CONCERNING LIMITATIONS IN INSPN & QUALITY CTL PROC USED DRG ENG OVERHAUL, WHICH RESULTED IN A FAILURE TO DETECT A FATIGUE CRACK, ORIGINATING FM A PREVIOUSLY UNDETECTED METALLURGICAL DEFECT IN A CRITICAL AREA OF THE STATE 1 FAN DISK. (SEE: NTSB/AAR-90/06)

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

THE INADEQUATE CONSIDERATION GIVEN TO HUMAN FACTORS LIMITATIONS IN THE INSPECTION AND QUALITY CONTROL PROCEDURES USED BY UNITED AIRLINES' ENGINE OVERHAUL FACILITY WHICH RESULTED IN THE FAILURE TO DETECT A FATIGUE CRACK ORIGINATING FROM A PREVIOUSLY UNDECTECTED METALLURGICAL DEFECT LOCATED IN A CRITICAL AREA OF THE STAGE 1 FAN DISK THAT WAS MANUFACTURED BY GENERAL ELECTRIC AIRCRAFT ENGINES. THE SUBSEQUENT CATASTROPHIC DISINTEGRATION OF THE DISK RESULTED IN THE LIBERATION OF DEBRIS IN A PATTERN OF DISTRIBUTION AND WITH ENERGY LEVELS THAT EXCEEDED THE LEVEL OF PROTECTION PROVIDED BY DESIGN FEATURES OF THE HYDRAULIC SYSTEMS THAT OPERATED THE DC-10'S FLIGHT CONTROLS.

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