United 232 Sioux City — Landing Without Hydraulics

On July 19, 1989, the fan disc of the tail-mounted engine on a McDonnell Douglas DC-10 operated by United Airlines exploded during cruise flight over Iowa. The fragments of the shattered titanium disc penetrated the horizontal stabilizer and destroyed all three of the aircraft's hydraulic systems — completely. Without any hydraulics, the DC-10's flight control surfaces could no longer be moved. The aircraft was, by every known standard, uncontrollable. And yet, the crew managed to fly for 44 minutes using a method previously thought impossible, saving 185 of the 296 people on board.

The DC-10 and Its Hydraulics — A Design Vulnerability

The McDonnell Douglas DC-10, a wide-body tri-jet, featured three independent hydraulic systems that powered all flight controls — ailerons, elevators, rudder, flaps, slats, spoilers, and landing gear. The critical design flaw: all three hydraulic lines ran in close proximity at one point — in the area of the tail assembly, directly beneath the number 2 tail-mounted engine.

This arrangement meant that a single catastrophic event at the tail could potentially destroy all three systems simultaneously. That is exactly what happened on that July day over Iowa.

Without hydraulics, the ailerons, elevators, and rudder had no function. The flaps and slats could not be deployed. Even the landing gear later had to be lowered by gravity. The pilots had literally no conventional means of controlling the aircraft's attitude.

The Crew — Four Men Against the Impossible

In the cockpit of United Flight 232 were three regular crew members:

• Captain Alfred C. Haynes — 57 years old, with United Airlines since 1956, over 29,000 flight hours. A calm, composed veteran known for his collegiality.
• First Officer William R. Records — Copilot who was flying the aircraft at the time of the engine failure.
• Flight Engineer Dudley J. Dvorak — Responsible for systems monitoring at his engineer's panel.

The fourth man, who became the decisive factor, happened to be on board:

• Captain Dennis E. Fitch — An off-duty DC-10 training captain for United Airlines, traveling as a passenger. Fitch was an expert on the DC-10 and had trained hundreds of scenarios in simulators — but never one without any hydraulics, because such a scenario was considered non-survivable and therefore was not trained.

3:16 PM — The Engine Explodes

United Flight 232 was a domestic service from Denver to Chicago with a stopover in Philadelphia. At 3:16 PM local time, at a cruising altitude of 37,000 feet (FL370) over northwestern Iowa, the fan disc of tail-mounted engine number 2 failed.

The fan disc — a massive titanium ring to which the engine's large fan blades are attached — had been weakened by a fatigue crack that originated during manufacturing 18 years earlier. Despite multiple inspections, the crack had never been detected. By July 19, 1989, it had propagated to the point where the disc burst under the enormous centrifugal forces.

Fragments of the titanium disc were hurled in all directions with tremendous energy. They penetrated the engine casing, the tail assembly, and — critically — all three hydraulic lines that converged at that point. Within seconds, the DC-10 lost all hydraulic fluid from all three systems. The controls were dead.

The Improvisation — Differential Thrust as a Control Method

Captain Haynes immediately recognized that conventional controls were no longer functional. The control column could be moved, but the control surfaces did not respond. Flight Engineer Dvorak confirmed: all three hydraulic systems depressurized.

When the public address system asked for any doctors or pilots in the cabin, Captain Fitch volunteered and was brought to the cockpit. What he saw confirmed his worst fears: total hydraulic loss. A scenario for which there was no procedure, no checklist, no training.

Fitch, however, had an idea: what if they used the two remaining engines — number 1 (left) and number 3 (right) — as a means of control? The theory was simple; the execution incredibly difficult:

• Turning: By applying differential thrust to the two engines, the aircraft could slowly be turned in a direction. More thrust on the right = left turn. More thrust on the left = right turn.
• Climbing and descending: By simultaneously increasing or decreasing thrust on both engines, the rate of descent could be influenced — but only roughly and with significant lag.
• Pitch control: The greatest challenge. Without elevators, the DC-10 was prone to a wave-like up-and-down motion (phugoid oscillation) that was extremely difficult to control.

Fitch took the position between the two pilot seats and operated both thrust levers directly. Haynes and Records continued attempting to exert influence through the control column, though it was practically ineffective. The four men worked in absolute coordination — every thrust lever input had to be precisely dosed and timed.

44 Minutes — The Path to Sioux City

The air traffic controllers at Minneapolis Center directed the crew to the nearest suitable airport: Sioux City Gateway Airport in Iowa. The controllers and the crew worked closely together to plan an approach that was feasible with the extremely limited controllability.

The 44 minutes between the engine failure and touchdown were a constant fight against physics. The aircraft described wide, irregular turns. The rate of descent fluctuated between zero and over 1,800 feet per minute. The phugoid oscillations caused the aircraft to pitch up and down regularly. On several occasions, the aircraft threatened to spiral out of control.

The atmosphere in the cockpit was remarkable. The Cockpit Voice Recorder (CVR) recordings reveal a crew that, despite the hopeless situation, remained professional and even displayed dry humor. When a controller asked which runway they wanted to land on, Haynes responded: "Whatever you got." When instructed to turn toward Runway 31, he replied: "We'll try." These remarks were not made out of cynicism but reflected a realistic assessment of the situation — the pilots knew they could only roughly aim the aircraft in a direction and would take whatever they could get.

4:00 PM — The Touchdown

At 4:00 PM, the DC-10 approached Sioux City Gateway Airport. The crew had lowered the landing gear by gravity — the only option without hydraulics. The flaps could not be deployed, which meant a significantly higher landing speed than normal.

In the final seconds of the approach, the aircraft's alignment was remarkably good. But immediately before touchdown, the right wing began to drop — a phugoid motion the pilots could no longer correct. The aircraft touched down at high speed (approximately 215 knots, nearly 250 mph / 400 km/h) and with a high rate of descent, with the right wing contacting the ground first.

The right wing broke off, engine number 3 separated, and the aircraft began rotating about its longitudinal axis. The DC-10 cartwheeled, broke into several sections, and caught fire. The aft fuselage section and the cockpit area were thrown the farthest.

The Toll — 185 Survivors

111 people lost their lives, including a lap infant who was not secured in a child restraint seat — a circumstance that later led to stricter regulations regarding children in aircraft. But the fact that 185 people (plus one lap infant) survived such an impact was considered nearly unbelievable by experts. Without the pilots' improvisation, no one would have survived.

CRM as a Case Study — Why the Team Functioned

United 232 is taught in pilot training worldwide as one of the most important examples of effective Crew Resource Management. The factors that positively influenced the outcome:

• Haynes' leadership style: Captain Haynes was not an authoritarian commander. He immediately recognized that he could not manage the situation alone and integrated Fitch without hesitation as an equal team member. He later said in lectures: "There is no cockpit built for one man alone."
• Fitch's expertise: As a DC-10 training captain, Fitch brought unique knowledge of the aircraft's systems. His spontaneous suggestion to use differential thrust as a control method was the salvation. Without him, the crew would likely not have come close to reaching an airport.
• Task distribution: Each crew member had a clear role: Haynes communicated and made decisions, Records assisted at the controls, Dvorak monitored systems and managed fuel, Fitch operated the thrust levers.
• Communication: Communication in the cockpit was open, direct, and respectful. Anyone could raise concerns at any time. There were no hierarchy barriers.
• Stress management: The occasional humor in the cockpit — such as Haynes' "I'll tell you what, I'll give you something I can't. I'll give you twelve miles" — was not a sign of recklessness but a proven mechanism for stress management that maintained cognitive function under extreme pressure.

The NTSB Investigation — Causes and Consequences

The NTSB investigation report identified the fatigue crack in the fan disc as the root cause. The crack had originated during the manufacturing of the titanium forging and had propagated slowly over 18 years and 38,839 engine cycles. Multiple inspections, including a fluorescent penetrant inspection (FPI), had failed to detect the crack — the inspection methods were not sensitive enough for the type of flaw involved.

The key recommendations and resulting changes:

• Improved inspection methods: The FAA mandated improved inspection procedures for engine rotor discs, including more sensitive ultrasonic testing. EASA subsequently adopted equivalent requirements for Trent, CF6, and other engine families used in European operations.
• Hydraulic system design: Aircraft manufacturers were directed to review the routing of hydraulic system lines and ensure that not all systems could be destroyed by a single event. Newer aircraft such as the Boeing 777 feature spatially separated hydraulic lines.
• Training for total hydraulic loss: The realization that differential thrust could function as emergency control was integrated into training programs. Pilots today train in simulators to control aircraft using thrust variation.
• Child restraint seats in aircraft: The death of a lap infant led to recommendations for mandatory child restraint seats in aircraft — a debate that continues to this day.
• Airport fire service positioning: The exemplary response of the Sioux City fire service — they had prepared for the emergency landing and were on scene immediately — became a standard for airport rescue and firefighting (ARFF) operations.

The Community of Sioux City

The response of the city of Sioux City to the disaster became a model for emergency management. The Iowa Air National Guard, whose base was located directly at the airport, was at the wreckage within seconds. Hospitals throughout the region had activated their emergency plans and were prepared. Volunteer helpers from across the community supported the professional rescue crews.

The city remains associated with the event to this day. A memorial at the airport honors the 112 victims (one additional victim died months later from injuries sustained in the crash). Survivors and residents of Sioux City maintain close bonds — regular memorial events bring both groups together.

Captain Haynes' Legacy

Alfred Haynes became one of the most prominent advocates for Crew Resource Management and aviation safety after the incident. Until his death in 2019, he delivered over a thousand lectures about the event, consistently emphasizing two points:

First: He insisted he was not a hero. He credited the team effort, the air traffic controllers, the fire service, and the community of Sioux City. His most famous quote: "There was no single hero. We had 44 minutes and were fortunate that many people made many right decisions."

Second: He used the incident to advocate for the importance of CRM training. He argued that the old culture of the "captain as God" — in which no one was allowed to question the pilot in command — was lethal. United 232 worked because four men operated as an equal team.

Lessons for Modern Aviation

United 232 changed aviation in multiple respects. Perhaps the most important takeaway is the most fundamental one: no single failure, however catastrophic, should render an aircraft uncontrollable. This principle has influenced the design of all subsequent transport aircraft and is embedded in both FAA (14 CFR Part 25) and EASA (CS-25) certification requirements.

At the same time, the incident demonstrated the limits of technology. In the end, it was not systems or automation that saved 185 lives, but human skill, improvisation, and teamwork. In an industry that increasingly relies on automation, United 232 remains a powerful reminder that fundamental flying skills and the ability to improvise must never be neglected.

The 185 survivors of Sioux City owe their lives to four pilots who attempted the impossible — and for 44 minutes, achieved the impossible.