Date: July 19, 1989 
Type: McDonnell-Douglas DC-10-10 
Registration: N1819U 
Operator: United Airlines 
Where: Sioux Gateway Airport, Iowa
Report No. NTSB-AAR-90-06 
Report Date: November 1, 1990 Pages: 126

Executive Summary:

On July 19, 1989, at 1516, a DC-10-10, N1819U, operated by United
Airlines as flight 232, experienced a catastrophic failure of the #2
tail-mounted engine during cruise flight.  The separation,
fragmentation, and forceful discharge of stage 1 fan rotor assembly
parts from the #2 engine led to the loss of the three hydraulic systems
that powered the airplane's flight controls.  The flightcrew
experienced severe difficulties controlling the airplane, which
subsequently crashed during an attempted landing at Sioux Gateway
Airport, Iowa.  There were 285 passengers and 11 crewmembers onboard.
One flight attendant and 110 passengers were fatally wounded.

The National Transportation Safety Board determines that the probable
cause of this accident was 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
undetected 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 operate the DC-10's flight

The safety issues raised in this report include:

1.  General Electric Aircraft Engines' (GEAE) CF6-6 fan rotor assembly
design, certification, manufacturing, and inspection.

2.  United Airlines' maintenance and inspection of CF6-6 engine fan
rotor assemblies.

3.  DC-10 hydraulic flight control system design, certification and
protection from uncontained engine debris.

4.  Cabin safety, including infant restraint systems, and airport
rescue and firefighting facilities.

Recommendations concerning these issues were addressed to the Federal
Aviation Administration, the Secretary of the Air Force, the Air
Transport Association and the Aerospace Industries Association.