United Airlines Flight 232

United Airlines Flight 232 was a regularly scheduled United Airlines flight from Stapleton International Airport in Denver to O'Hare International Airport in Chicago, continuing to Philadelphia International Airport in Philadelphia, United States. On July 19, 1989, the McDonnell Douglas DC-10 serving the flight crash-landed at Sioux Gateway Airport in Sioux City, Iowa, after suffering a catastrophic failure of its tail-mounted engine due to an unnoticed manufacturing defect in the engine's fan disk, which resulted in the loss of all flight controls. Of the 296 passengers and crew on board, 112 died during the accident, while 184 people survived. Thirteen passengers were uninjured.

Despite the fatalities, the accident is considered a good example of successful crew resource management, still a relatively new concept at the time. Contributing to the outcome was the crew's decision to recruit the assistance of a company check pilot, on board as a passenger, to assist controlling the aircraft and troubleshooting of the problem the crew was facing.

Haynes' co-pilot was First Officer William R. "Bill" Records, 48. He estimated that he had approximately 20,000 hours of total flight time. He was hired first by National Airlines in 1969. He worked subsequently for Pan American World Airways. He was hired by United in 1985, and had accrued 665 hours as a DC-10 first officer while at United.

ATC asked the crew to make a left turn to keep them clear of the city:

Haynes later noted, "We were too busy [to be scared]. You must maintain your composure in the airplane, or you will die. You learn that from your first day flying."

Crash landing

200px|thumb|View of the initial touchdown area

As the crew began to prepare for arrival at Sioux Gateway Airport, they questioned whether they should deploy the landing gear or belly-land the aircraft with the gear retracted. They decided that having the landing gear down would provide some shock absorption on impact. The complete hydraulic failure left the landing gear lowering mechanism inoperative. Two options were available to the flight crew. The DC-10 is designed so that if hydraulic pressure to the landing gear is lost, the gear will fall down slightly and rest on the landing gear doors. Placing the regular landing gear handle in the down position will unlock the doors mechanically, and the doors and landing gear will then fall down into place and lock due to gravity. This lever has the added benefit of unlocking the outboard ailerons, which are not used in high-speed flight and are locked in a neutral position.

Fitch continued to control the aircraft's descent by adjusting engine thrust. With the loss of all hydraulics, the flaps could not be extended, and since flaps control both the minimum required forward speed and sink rate, the crew was unable to control either the airspeed or the sink rate. On final approach, the aircraft's forward speed was and it had a sink rate of , while a safe landing would require forward speed and sink rate. 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. It was now 16:00.

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. The tail section broke off from the force of the impact, and the rest of the aircraft bounced several times, shedding the landing gear and engine nacelles and breaking the fuselage into several main pieces. 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. Witnesses reported that the aircraft "cartwheeled" end-over-end, but the investigation did not confirm this. Many of the children were traveling alone.

Rescuers did not identify the debris that was the remains of the cockpit, with the four crew members alive inside, until 35 minutes after the crash. All four recovered from their injuries and eventually returned to flight duty. according to a United pilot who flew with Fitch, "Most of the simulations never even made it close to the ground" with the aircraft under control. The NTSB stated that "under the circumstances the UAL (United Airlines) flight crew performance was highly commendable and greatly exceeded reasonable expectations." The last passenger version of the DC-10 flew in 2014, although freighter versions continued to operate until late 2022.

Because this type of aircraft control (with loss of control surfaces) is difficult for humans to achieve, some researchers have attempted to integrate this control ability into the computers of fly-by-wire aircraft. Early attempts to add the ability to real airplanes were not very successful; the software was based on experiments performed in flight simulators where jet engines are usually modeled as "perfect" devices with exactly the same thrust on each engine, a linear relationship between throttle setting and thrust, and instantaneous response to input. Later, computer models were updated to account for these nonlinear factors, and aircraft such as the F-15 STOL/MTD have been flown successfully with this software installed.

Titanium processing

The manufacturing process for titanium was changed to eliminate the type of gaseous anomaly that served as the starting point for the crack. Newer batches of titanium use much higher melting temperatures and a "triple vacuum" process in an attempt to eliminate such impurities (triple melt VAR).

Aircraft designs

Newer aircraft designs have incorporated hydraulic fuses to isolate a punctured section and prevent a total loss of hydraulic fluid. After the United 232 accident, such fuses were installed in the number three hydraulic system in the area below the number two engine on all DC-10 aircraft to ensure sufficient control capability remained if all three hydraulic system lines should be damaged in the tail area.

Restraints for children

Of the four children deemed too young to require seats of their own ("lap children"), one died from smoke inhalation. The accident began a campaign directed by United Flight 232's senior flight attendant, Jan Brown Lohr, for all children to have seats on aircraft.

The argument against requiring seats on aircraft for children younger than age two is the higher cost to a family of having to buy a seat for the child, and this higher cost will motivate more families to drive instead of fly, and incur the much greater risk of driving (see epidemiology of motor vehicle collisions). 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.

Though it is no longer on the "most wanted" list, providing aircraft restraints for children younger than age two is still recommended practice by the NTSB and FAA, though it is not required by the FAA as of May 2016. The NTSB asked the International Civil Aviation Organization to make this a requirement in September 2013.

Crew resource management

The accident has since become an example of successful crew resource management (CRM).

Haynes also credited CRM as being one of the factors that saved his own life, and many others.

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

As with the Eastern Air Lines Flight 401 crash of a similarly sized Lockheed L-1011 in 1972, the relatively shallow angle of descent likely played a large part in the relatively high survival rate. The National Transportation Safety Board concluded that under the circumstances, "a safe landing was virtually impossible".

John Kenneth Stille – chemist

Survivors

Spencer Bailey – writer, editor, and journalist
Helen Young Hayes – investment fund manager
Al Haynes – captain of UA232
Michael R. Matz – Olympian and racehorse trainer
Jerry Schemmel – former radio broadcaster for the Colorado Rockies and Denver Nuggets
Pete Wernick – banjo player and member of American bluegrass ensemble Hot Rize, who managed to resume performing two days after the crash

Depictions

The accident was the subject of 11th-season episode 13 of the documentary series Mayday (also known as Air Crash Investigation), titled "Impossible Landing" (13 April 2012). The episode featured interviews with survivors and showed actual footage of the crash.
The accident was the subject of the 1992 television movie A Thousand Heroes, also known as Crash Landing: The Rescue of Flight 232.
The episode "Engineering Disasters" (season 6, episode 18) of Modern Marvels featured the crash.
The accident was featured in an episode of Seconds from Disaster (S2E7 9/13/05 "Crash Landing in/at Sioux City") on the National Geographic Channel and MSNBC Investigates on the MSNBC news channel.
The History Channel distributed a documentary named Shockwave; a portion of Episode 7 (originally aired January 25, 2008) detailed the events of the crash.
The episode "A Wing and a Prayer" of Survival in the Sky (UK title: Black Box) featured the accident.
The Biography Channel series I Survived... explained in detail the events of the crash through passenger Jerry Schemmel, flight attendant Jan Brown Lohr, and pilot Alfred Haynes.
The episode "Crisis in the Cockpit" (Season 2, Episode 1) of Why Planes Crash on The Weather Channel featured the accident.
The 1999 play Charlie Victor Romeo (made into a film in 2013) dramatically reenacted the incident using transcripts from the cockpit voice recorder (CVR).
The 1991 novel Cold Fire, by Dean Koontz, includes a fictional crash based on Flight 232.
The 1993 film Fearless portrayed a fictional plane crash based in part on the crash of Flight 232.
In 2016, The House Theatre of Chicago produced United Flight 232. The play was a new work directed and adapted by Vanessa Stalling and based on the book Flight 232 by Laurence Gonzales. Surviving crew members attended the play in April 2016, and the production was subsequently nominated for six Equity Jeff Awards, winning two.
In 2021, the accident was covered in episode 5 of the UK TV series Plane Crash Recreated.

Survivor accounts

Dennis Fitch described his experiences in Errol Morris's television show First Person, episode "Leaving the Earth".
Flight 232: A Story of Disaster and Survival by Laurence Gonzales (2014, W. W. Norton & Company; ).
Miracle in the Cornfield – an inside survivor narrative by Joseph Trombello (1999, PrintSource Plus, Appleton, WI; )
When the World Breaks Your Heart: Spiritual Ways of Living With Tragedy by Gregory S. Clapper, a chaplain in the National Guard who relates the stories of some of the survivors he aided in the aftermath of the crash (1999; 2016, Wipf and Stock; )
Chosen to Live: The Inspiring Story of Flight 232 Survivor Jerry Schemmel by Jerry Schemmel with Kevin Simpson (Victory Pub. Co.,1996; ).
Spencer Bailey discussed his experiences on the Time Sensitive podcast, in a 2019 interview with Andrew Zuckerman.

Flight 232 Memorial

thumb|right|Flight 232 Memorial

The Flight 232 Memorial was built along the Missouri River in Sioux City, Iowa, to commemorate the heroism of the flight crew and the rescue efforts the Sioux City community undertook after the crash. 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.

Similar accidents

The odds against all three hydraulic systems failing simultaneously had previously been calculated as low as a billion to one. Yet such calculations assume that multiple failures must have independent causes, an unrealistic assumption, and similar flight control failures have indeed occurred:

In 1971, a Boeing 747, operating as Pan Am 845, struck approach light structures for the reciprocal runway as it lifted off the runway at San Francisco Airport. Major damage to the belly and landing gear resulted, which caused the loss of hydraulic fluid from three of its four flight control systems. The fluid which remained in the fourth system gave the captain very limited control of some of the spoilers, ailerons, and one inboard elevator. That was sufficient to circle the plane while fuel was dumped and then to make a hard landing. There were no fatalities, but there were some injuries.
In 1981, a Lockheed L-1011, operating as Eastern Air Lines Flight 935, suffered a similar failure of its tail-mounted number two engine. The shrapnel from that engine inflicted damage on all four of its hydraulic systems, which were also close together in the tail structure. Fluid was lost in three of the four systems. The fourth hydraulic system was struck by shrapnel, but not punctured. The hydraulic pressure remaining in that fourth system enabled the captain to land the plane safely with some limited use of the outboard spoilers, the inboard ailerons, and the horizontal stabilizer, plus differential engine power of the remaining two engines. There were no injuries.
In 1985, Japan Air Lines Flight 123, a Boeing 747-146SR, suffered a rupture of the pressure bulkhead in its tail section, caused by undetected damage during a faulty repair to the rear bulkhead after a tailstrike seven years earlier. Pressurized air subsequently rushed out of the bulkhead and blew off the plane's vertical stabilizer, also severing all four of its hydraulic control systems. The pilots were able to keep the plane airborne for 32 minutes using differential engine power, but without any hydraulics or the stabilizing force of the vertical stabilizer, the plane eventually crashed in mountainous terrain. There were only 4 survivors among the 524 on board. This accident is the deadliest single-aircraft accident in history.
In 1994, RA85656, a Tupolev Tu-154 operating as Baikal Airlines Flight 130, crashed near Irkutsk shortly after departing from Irkutsk Airport, Russia. Damage to the starter caused a fire in engine number two (located in the rear fuselage). High temperatures during the fire destroyed the tanks and pipes of all three hydraulic systems. The crew lost control of the aircraft. The out-of-control plane, at a speed of 275 knots, hit the ground at a dairy farm and burned. All 124 passengers and crew, as well as a dairyman on the ground, died.
In 2003, OO-DLL, a DHL Airbus A300, was struck by a surface-to-air missile shortly after departing from Baghdad International Airport, Iraq. The missile struck the port-side wing, rupturing a fuel tank and causing the loss of all three hydraulic systems. With the flight controls disabled, the crew used differential thrust to execute a safe landing at Baghdad.
In 2024, an Embraer 190, operating as Azerbaijan Airlines Flight 8243, was hit by a Russian anti-air system, rupturing all three hydraulic lines, rendering the plane inoperable. After diverting from the original destination of Grozny, Russia, the pilots decided to cross the Caspian Sea to attempt a landing in Kazakhstan. The pilots flew for more than 70 minutes with no control surfaces before crashing on a third attempt to land at Aktau International Airport. Of the 67 people on board, 38 died, including three out of five crewmembers.

The disintegration of a turbine disc, leading to loss of control, was a direct cause of two major aircraft disasters in Poland:

On March 14, 1980, LOT Polish Airlines Flight 007, an Ilyushin Il-62, attempted a go-around when the crew experienced troubles with a gear indicator. When thrust was applied, the low-pressure turbine disc in engine number 2 disintegrated because of material fatigue; parts of the disc damaged engines number 1 and 3 and severed control pushers for both horizontal and vertical stabilizers. After 26 seconds of uncontrolled descent, the aircraft crashed, killing all 87 people on board.
On May 9, 1987, improperly assembled bearings in Il-62M engine number 2 on LOT Polish Airlines Flight 5055 overheated and exploded during cruise over the village of Lipinki, causing the shaft to break in two; this caused the low-pressure turbine disc to spin to enormous speeds and disintegrate, damaging engine number 1 and cutting the control pushers. The crew managed to return to Warsaw, using nothing but trim tabs to control the crippled aircraft, but on the final approach, the trim controlling links burned and the crew completely lost control over the aircraft. Soon after, it crashed on the outskirts of Warsaw; all 183 on board died. Had the plane stayed airborne for 40 seconds more, it would have been able to reach the runway.

In contrast to deploying landing gear:

On August 15, 2019, Ural Airlines Flight 178, an Airbus A321, encountered a flock of seagulls resulting in a bird strike that caused fires in both CFM56-5 engines just after takeoff from Zhukovsky International Airport, Moscow, Russia. Due to a failure to follow standard operating procedures, the plane was forced to land in a corn field with the landing gear raised. The pilots claimed they intentionally landed with the landing gear up, though the CVR recording revealed no discussion about this. Everyone on board the flight survived. 74 people were injured, none severely.

Notes

References

External links

NTSB Accident report of United Airlines Flight 232
Alternate link at Embry–Riddle Aeronautical University
Cockpit voice-recorder transcript (pdf) (NB contains error)
A talk given by the pilot describing the crash at NASA Dryden in 1991
Siouxland Chamber Of Commerce: Remembering Flight 232 (Picture of memorial depicting Lt. Colonel Dennis Nielsen carrying Spencer Bailey)
"17th Anniversary Tribute of Flight 232"
News report with video of crash landing of Flight 232, ABC News, July 19, 1989
Pre-crash photos from Airliners.net
Martha Conant tells her story of surviving the crash.
– 1992 TV movie
Errol Morris' First Person (one hour documentary video, accident recounting by Denny Fitch)