was a scheduled flight operated by
United Airlines between
Denver and
Philadelphia via
Chicago . On
July 19 ,
1989 , the
Douglas DC-10 (Registration ) being operated for this flight suffered an uncontained failure of its number 2 engine (mounted in the tail), which destroyed all three of the aircraft's hydraulic systems. With no controls working except the power levers for the two remaining engines, it broke up during an
Emergency Landing on the runway at
Sioux City, Iowa , killing 110 of its 285 passengers and one of the 11 crew members.
Owing to the skill of the crew and a DC-10 instructor pilot, 175 passengers and 10 crew members survived the crash, which is considered a textbook example of successful
Crew Resource Management , due to the effective use of all the resources available aboard the plane for help during the emergency.
How Swift Starting Action Teams Get off the Ground: What United Flight 232 and Airline Flight Crews Can Tell Us About Team Communication ''Management Communication Quarterly'', Vol. 19, No. 2, November 2005
report.]]
The flight took off at 14:09 ( of its tail-mounted
General Electric CF6-6 engine broke in two. The fan cowling was blown off and pieces of the engine penetrated the aircraft tail section in numerous places, including both horizontal stabilizers. Pieces of shrapnel which went through the right horizontal stabilizer severed the lines of all three hydraulic systems, allowing the fluid to drain away.
1
Captain
Alfred C. Haynes and his flight crew (First Officer William Records, who was flying, and Second Officer Dudley Dvorak, flight engineer) felt a jolt going through the aircraft, and warning lights showed that the
Autopilot had disengaged, and the tail-mounted number two engine was malfunctioning. The co-pilot noticed that the airliner was off course, and moved his
Control Column to correct this, but the plane did not respond. The flight crew discovered that the pressure gauges for each of the three hydraulic systems were registering zero, and they realized that the initial failure had left all
Control Surfaces immovable. The three hydraulic systems were separated such that a single event in one system would not disable the other systems, but beyond that there was no backup system, a fact which the NTSB later recommended be remedied.
2
The plane had a continual tendency to turn right, and was difficult to maintain on a stable course. It began to slowly oscillate vertically in a
Phugoid cycle, which is characteristic of planes in which hydraulic power is lost. With each iteration of the cycle the aircraft lost approximately 1500 feet of altitude.
Dennis E. Fitch , a DC-10
Flight Instructor , was
Deadheading as a passenger on the plane and offered his assistance. After entering the cockpit, Fitch discovered that the only available method of controlling the aircraft was through adjusting the throttles of the remaining two engines; running one engine faster than the other to turn the plane (differential thrust), and accelerating or decelerating in order to gain or lose altitude. Using this method, it was possible to mitigate the phugoid cycle and make rough steering adjustments. At one point Fitch manually lowered the landing gear in flight, hoping that this would force trapped hydraulic fluid back into the lines allowing some movement of control surfaces. Although the gear lowered successfully, there was no improvement in control response as all the fluid had been lost through the punctured lines.
Air Traffic Control (ATC) was contacted and an emergency landing at nearby
Sioux Gateway Airport was organized.
Haynes kept his sense of humor during the emergency, as recorded on the plane's
CVR :
:Fitch: ''I'll tell you what, we'll have a
Beer when this is all done.
:Haynes: ''Well I don't drink, but I'll sure as hell have one.
and later:
:Sioux City Approach: ''United Two Thirty-Two Heavy, the wind's currently three six zero at one one; three sixty at eleven. You're cleared to land on any runway.''
:Haynes: ''
Roger. [laughter You want to be particular and make it a runway, huh?''
3
A more serious remark often quoted from Haynes was made when ATC asked the crew to make a left turn to keep them clear of the city:
:Haynes: ''Whatever you do, keep us away from the city.''Macarthur Job (1996). ''Air Disaster Volume 2'', Aerospace Publications, ISBN 1-875671-19-6: pp.186-202
Landing was originally planned on the 9,000
Foot (2743 m)
Runway 31. The difficulties in controlling the aircraft made lining up almost impossible. While dumping excess fuel, the plane executed a series of mostly right-hand turns (it was easier to turn the plane in this direction) with the intention of coming out at the end lined up with runway 31. When they came out they were instead left with an approach on the shorter Runway 22 of 6,600 feet (2012 m), with little capacity to maneuver.
4
Fire trucks had been placed on runway 22,
Eyewitness Report, United Airlines Flight 232 Airdisaster.com, by Captain Al Haynes anticipating a landing on runway 31, and there was a scramble as the trucks rushed out of the way. Fortunately, all the
Vehicles parked there got out of the way before the plane touched down.
Fitch continued to control the aircraft's descent by adjusting engine thrust. With the loss of all hydraulics, the crew were unable to control airspeed independent from sink rate. On final descent, the aircraft was going 240 knots and sinking at 1850 feet per minute, while a safe landing would require 140 knots and 300 feet per minute. The aircraft began to sink faster while on final approach and veer to the right. The tip of the right wing hit the runway first, 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. On the final impact the right wing was sheared off and the main part of the aircraft skidded sideways, rolled over on to its back, and slid to a stop upside down on the right side of runway 22. Witnesses reported that the aircraft ed but the investigation did not confirm this.
5 News reports that the aircraft cartwheeled were due to misinterpretation of the video of the crash that showed the flaming right wing tumbling end-over-end.
111 people died in the crash. Most were killed by injuries sustained in the multiple impacts, but many in the middle fuselage section directly above the fuel tanks died from smoke inhalation in the post-crash fire, which burned for longer than it might have due to delays in the firefighting efforts. 185 people survived the accident, the majority of them from the second-class seating ahead of the wings (one of the crash survivors died a month later of his injuries). Many passengers were able to walk out through the ruptures to the structure, and in many cases got lost in the high field of
Corn adjacent to the runway until rescue workers arrived on the scene and escorted them to safety.
Investigation attributed the cause of the fracture of the fan disk to a failure of
United Airlines maintenance processes to detect an existing
Fatigue crack.
6 Post-crash analysis of the crack surfaces showed the presence of the penetrating fluorescent dye used to detect cracks during maintenance, indicating that the crack was present and should have been detected at a prior inspection. The detection failure arose from poor attention to
Human Factors in United Airlines' specification of maintenance processes.
The crack in the fan disk was traced back to the
Alcoa Foundry from which the engine part was sourced. It turned out that there was a defect in elimination of gaseous anomalies during the purifying of the
Titanium disk ingot. An excess amount of
Nitrogen was in the material, causing a 'hard alpha
Inclusion ' which cracked during forging and then fell out during final machining, forming a cavity with microscopic cracks at the edges. During the engine's normal running cycle, one of these cracks grew slowly each time the engine was powered up and brought to operating temperature, until it grew large enough for the disk to fail structurally.
7 Newer batches used much higher melting temperatures and a 'triple vacuum' process to eliminate these impurities.
The subsequent investigation and airworthiness directive also revealed several other fan disks already in service from the same batch of ingots which had started to exhibit the initial cracking symptoms of part failure.
Some portions of the aircraft that had broken away when the fan disk failed were later found in farm fields along the flight path.
The
National Transportation Safety Board investigation reported that after subsequent reconstructions of the accident in
Flight Simulator s, it was deemed that training for such an event involved too many factors to be practical. While some level of control was possible, no precision could be achieved and a landing under these conditions was stated to be "a highly random event". The NTSB further noted that "under the circumstances the UAL flightcrew performance was highly commendable and greatly exceeded reasonable expectations."
8
Because this type of aircraft control is difficult for humans to achieve, some researchers have attempted to integrate this control ability into the
Computer s of
Fly-by-wire aircraft. Early attempts to add the ability to real planes were not very successful, the software having been based on experiments conducted in flight simulators where
Jet Engine s are usually modeled as "perfect" devices with exactly the same thrust on each engine. Later, programming was updated to compensate for the problem, and planes have been successfully flown with this software installed.
9 However, it remains a rarity on commercial aircraft.
The odds against all three hydraulic systems failing simultaneously had previously been calculated as high as a billion to one, but a similar failure had occurred just four years previously when
Japan Airlines Flight 123 suffered a structural failure that left it without any hydraulic controls.
Newer aircraft designs such as the MD-11 have incorporated
Hydraulic Fuse s to isolate a punctured section and prevent a total loss of hydraulic fluid; this was also partially implemented on DC-10 models after the accident.
Of the four children deemed too young to have seats of their own (so called 'lap children'), one died from smoke inhalation. Despite the survival rate for the lap children being a little higher than that of the passengers (75% versus 62.5%), the
NTSB added a safety recommendation to the
FAA on its "List of Most Wanted Safety Improvements," the response to which was flagged on NTSB's website as an "acceptable response, progressing slowly." It also sparked a campaign, led by United Flight 232's senior flight attendant, Jan Brown Lohr, for all children to have seats on aircraft.
10
Of the 296 people aboard, 111 were killed in the crash, while 185 survived. Captain Haynes later told of three contributing factors regarding the actual time of day that allowed for a better chance of survival:
# The incident occurred during daylight hours;
# The incident occurred as a shift change was occurring at both a regional trauma center and a regional burn center in Sioux City, allowing for more medical personnel to treat the injured; and
# The incident occurred when the Iowa Air National Guard was on duty at Sioux Gateway Airport, allowing for 285 trained personnel to assist with
Triage and evacuation of the wounded.
"Had any of those things not been there," Haynes said later, "I'm sure the fatality rate would have been a lot higher."Nicholas Faith (1996, 1998). ''Black Box'', Boxtree, ISBN 0-7522-2118-3: pp.158-165
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."
- Spencer Bailey - Subject of a famous photograph showing Lt. Colonel Dennis Nielsen carrying the three-year-old survivor to safety. A statue in part of Sioux City's riverfront development is based on the picture. The 1994 memorial commemorates the rescue efforts by the Sioux City community following the crash, featuring contemplative areas and a tree-lined approach with plaques describing the incident.
- Jerry Schemmel - Radio announcer for the Denver Nuggets , an NBA basketball team. Also wrote a book about United Airlines Flight 232 titled ''Chosen to Live'', and was credited with saving the life of a child in the crash.
- Michael R. Matz - Trainer of the 2006 Kentucky Derby favorite and winner, Barbaro . Also credited with saving the lives of four children in the crash, three of whom were in the same family.
- Dennis E. Fitch - A safety consultant to NASA as a member of the Aerospace Safety Advisory Panel and has been inducted into the Aviation Hall Of Fame at the Smithsonian National Air And Space Museum . Also a DC-10 pilot and instructor, he helped Captain Al Haynes fly United Airlines Flight 232. "For the thirty minutes I was up there," Fitch said later, "I was the most alive I've ever been. That is the only way I can describe it to you."
- Joseph Trombello - Wrote a book about United Airlines Flight 232 titled ''Miracle in the Cornfield''.
- Pete Wernick - Prominent banjo player with the Hot Rize group and instructor, was on his way to a festival in the Albany, NY area. Walked away with his banjo and took the next flight to make the gig. Gave his personal account of the days events in the song, "A Day in '89 (You Never Know)"; Wernick has yet to release a recording of the song, but has published the lyrics on his website. Lyrics to Pete Wernick's "A Day in '89 (You Never Know)" from drbanjo.com (Wernick's official site)
- Jan Brown Lohr - United 232's Senior Flight Attendant. She was forced by regulation to ask parents with "lap babies" (children without seats) aboard flight 232 to place their children on the cabin floor during the flight's final moments before impact. Upon impact one of four children was killed. The deceased child's mother came to her at the crash site and stated "You told me to put my baby on the floor and now he's gone." Since then, Lohr has tirelessly lobbied in Washington D.C. to promote the safety of children on all civilian aircraft and airlines, asking that federal regulations require all children to have a seatbelt on every flight.
- While not mentioning the accident with words, a music video featuring a man who was in a plane crash with survivors walking out of corn fields while trying to see his wife back at home was made by Brian McKnight for his song Back At One .
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