Like other widebody transport aircraft of the time,[1]: 100  the DC-10 was not designed to revert to unassisted manual control in the event of total hydraulic failure.

[1]: 1 At 15:16, while the airplane was making a slight right turn at its cruising altitude of 37,000 feet (11,000 m), the fan disk of its tail-mounted General Electric CF6-6 engine disintegrated explosively.

[1]: 1  The crew contacted United Airlines maintenance personnel via radio, but were told that the possibility of a total loss of hydraulics in a DC-10 was considered so remote that no procedure had been established for such an event.

[1]: 76 The airplane was tending to pull right and oscillated slowly vertically in a phugoid cycle – characteristic of planes in which control surface command is lost.

Air traffic control (ATC) was contacted and an emergency landing at nearby Sioux Gateway Airport was organized.

ATC also advised that a four-lane Interstate highway ran north and south just east of the airport, which they could land on if they did not think they could make the runway.

Moments before landing, the roll to the right suddenly worsened significantly and the aircraft began to pitch forward into a dive; Fitch realized this and pushed both throttles to full power in a desperate, last-ditch attempt to level the plane.

[1]: 23  The CVR recorded these final moments:[17] The engines were not able to respond to Fitch's controls in time to stop the roll, and the airplane struck the ground with its right wing, spilling fuel which ignited immediately.

At final impact, the right wing was torn off and the main part of the aircraft skidded sideways, rolled over onto its back, and slid to a stop upside-down in a corn field to the right of Runway 22.

Most were killed by injuries sustained during the multiple impacts, but 35 people in the middle fuselage section directly above the fuel tanks died from smoke inhalation in the post-crash fire.

[20] Three months after the crash, a farmer discovered most of the fan disk, with several blades still attached, in her cornfield, thereby qualifying her for a reward, as a General Electric lawyer confirmed.

The NTSB determined that the probable cause of this accident was the inadequate consideration given to human factors, and limitations of the inspection and quality control procedures used by United Airlines' engine overhaul facility.

These resulted in the failure to detect a fatigue crack originating from a previously undetected metallurgical defect located in a critical area of the titanium-alloy stage-1 fan disk that was manufactured by General Electric Aircraft Engines.

Despite the ferocity of the accident, 184 (62.2%) passengers and crew survived owing to a variety of factors including the relatively controlled manner of the crash and the early notification of emergency services.

The investigation, while praising the actions of the flight crew for saving lives, later identified the cause of the accident as a failure by United Airlines maintenance processes and personnel to detect an existing fatigue crack.

[1]: 75–76, 87  The Probable Cause in the report by the NTSB read as follows: 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 detection failure arose from poor attention to human factors in United Airlines' specification of maintenance processes.

After the double vacuum process, the ingot was shaped into a billet, a sausage-like form about 16 inches in diameter, and tested using ultrasound to look for defects.

[1]: 77 The origins of the crash disk are uncertain because of significant irregularities and gaps, noted in the NTSB report, in the manufacturing records of GE Aircraft Engines (GEAE) and its suppliers.

[1]: 80  Records found after the accident indicated that two rough-machined forgings having the serial number of the crash disk had been routed through GEAE manufacturing.

Alcoa records indicate that this RMI titanium billet was first cut in 1972 and that all forgings made from this material were for airframe parts.

"[1]: 81 The NTSB investigation, after reconstructions of the accident in flight simulators, deemed that training for such an event involved too many factors to be practical.

[22] The NTSB stated that "under the circumstances the UAL (United Airlines) flight crew performance was highly commendable and greatly exceeded reasonable expectations.

[23] The manufacturing process for titanium was changed to eliminate the type of gaseous anomaly that served as the starting point for the crack.

Losing all three hydraulic systems remained possible if serious damage occurs elsewhere, as nearly happened to a cargo DC-10-40F in April 2002 during takeoff in San Salvador when a main-gear tire exploded after running over a lost thrust reverser cascade.

The FAA estimates that a regulation that all children must have a seat would equate, for every one child's life saved on an aircraft, to 60 people dying in highway accidents.

…the preparation that paid off for the crew was something … called cockpit resource management… Up until 1980, we kind of worked on the concept that the captain was THE authority on the aircraft.

[37]When Haynes died in August 2019, United Airlines issued a statement thanking him for "his exceptional efforts aboard Flight UA232".

It features a statue of Iowa National Guard Lt. Col. Dennis Nielsen from a news photo that was taken that day while he was carrying a three-year-old to safety.

[53] Yet such calculations assume that multiple failures must have independent causes, an unrealistic assumption, and similar flight control failures have indeed occurred: The disintegration of a turbine disc, leading to loss of control, was a direct cause of two major aircraft disasters in Poland: In contrast to deploying landing gear: