Accident Analysis United Flight 232

Accident Analysis United Flight 232

In the world of aviation accidents are bound to happen, given the large number of take offs and landings that take place each day. To prevent accidents as much as possible requires doing some type of accident analysis. This is where investigators will evaluate the causes of why an accident occurred. Where, they will look carefully at the various pieces of data, analyze the flight data recorder, look at the airplane itself and weather conditions. In the case of Untied Airline flight 232, this incident underscores several different lessons that could be learned to prevent accidents in the future. To fully understand this requires examining the events that led up to the crash and shortcomings that would lead to the tragedy. Together these two elements will provide the greatest insights as to what were the main factors that caused the accident to occur.

History of United Airlines Flight 232

United flight 232 was operating on its regularly scheduled route of traveling from Stapleton International Airport in Denver, Colorado to it final destination of Philadelphia International. On route, the plane was scheduled to make a routine stop at Chicago O' Hare. On July 19, 1989, the plane would take off as usual from Denver. However, on route to Chicago a mechanical failure would occur near Sioux City, Iowa. What happened was once the plane had reached it cruising altitude, the crew radioed that they were having trouble with plane responding to commands from the pilots. They would continue to wrestle with this problem for 30 minutes, at which point they would lose control of the aircraft and it would crash into a corn field near Sioux City, Iowa. There were a total of 289 passengers on board, with 11 crew members. The weather conditions were: an estimated ceiling of 4,000 feet, with scattered clouds and 15 miles of visibility. The wind direction was shifting between 10 degrees at 11 knots and 360 degrees at 14 knots. The flight crew was considered to be very experienced. With the Captain having a total of 29,967 hours of total flight time, on the airplane that they were flying (the DC 10) he had a total of 7,190 hours and had been flying with the airline since 1956. The First Officer had 20,000 hours of flight time and had 665 hours of flight time on the DC 10. The Second Officer had 15,000 hours of flight time and 33 hours on the DC 10. There was also an off duty Captain to assist in case of an emergency. His qualifications were a total of 23,000 flight hours and 2,987 hours in the airplane. (Krause, 2003)

The Events that would Lead to the Accident

United flight 232 took off from Denver at the usual time of 1:00 PM. About one hour and seven minutes into the flight the crew heard a loud bang that was preceded by shutter then a shimmying sound (near the frame of aircraft). After checking the various instruments it was determined that the number two tail mounted engine had failed. The crew attempted to shut off the power to the rear engine, but it was not responding to their commands. Instead, they would have to manually cut off all fuel going into the malfunctioning engine. As this was occurring, the Second Officer reported that all of the instruments were at zero, while the First Officer informed the Captain that he had lost all control of the aircraft. After confirming what was occurring, the Captain prepared to make an emergency landing in Sioux City, Iowa and informed the flight attendants as well as the passengers of the situation. It was at this time, that the off duty Captain began to assist with the situation after being informed of what was occurring by the Captain of the flight crew. Running out of options, the crew looked out the window to try and visually confirm the overall extent of the damage. However, as this was taking place, the crew would lose control of the airplane, where both the Captain and the First Officer had to struggle to keep the plane level. It was at this point, that the remaining fuel was dumped and it appeared as if the flight would not be able to make to Sioux City. With the Captain saying, "We're not going to make it to the runway fellas." (Krause, 2003) it was at this time that the Captain informed the flight attendants to prepare the cabin for an emergency landing in an open field. As this was taking place, the plane began to experience wild gyrations called a phugoid. This is where the airplane will swing back and fourth in a zig zag type of formation. As a result, controlling the airplane would be difficult given the ability to maintain control and the fact that they were making an emergency landing in a corn filed. When the plane was making its decent, the flight crew would have trouble maintaining control of the plane, as it moved closer to the ground. About 100 feet from their intended approach, the Captain reported that the right wing was veering too far and than the nose of the aircraft continued to slope downward (despite all attempts by the crew to level it out). When the plane was touching down the right wing would make initial contact with the ground, followed by the right landing gear. At which point, the plane would skid to the right of the runway, spinning around in a vertical position. During the initial touch down, is when eyewitnesses would claim that the aircraft immediately would catch fire. This is when it was going through the rough landing, as it would quickly begin to break apart, with the right wing being the first piece of the aircraft to separate itself from the debris. At which point, the cockpit and the engines would separate during the landing, leaving a large portion of the fuselage and the left wing attached. Where, debris was clearly scattered all across the field that the plane landed, near the runway of the Sioux City airport. ("United Airlines Flight 232," 1990)

The Investigation and Results

After the crash the National Transportation and Safety Board (NTSB) would conduct an assessment of what were the causes that helped contribute to the crash. After an extensive investigation, they found that the situation was a combination of several different factors to include: human error at the United maintenance facility, DC 10 hydraulic / flight control issues, problems with the manufacture of engine (GE Aircraft Engines), cabin safety and improved coordination for first responders. When looking at the first issue, human error at the United maintenance facility, it is clear that this a major factor that helped contribute to the accident. What happened was a failure occurred in rear engine number 2. Where, within the metal of a vital part of the fan, there was a sizeable crack. This was not discovered by the inspection personnel at the United maintenance facility. Over the course of time, as the engine would continue to operate the crack would provide less support to the fan when the engine is in operation. During United flight 232, this crack became so weak that debris would break off, causing it to go into the rear engine. At which point, it would only be matter of seconds until the engine would no longer respond. In the NTSB report, they specifically cite human error during the inspection process at the maintenance facility as to one reason why the accident occurred. To prevent such issues from occurring in the future, the report recommends that the airline begin using additional technology to inspect the various working parts of the aircraft in conjunction with visual confirmation. The thinking is that the crack in rear engine number two was so small that the human eye could not possibly be able to identify the issue. Therefore, the report recommends having a third set of eyes, to see those cracks that are too small to be identified with a visual inspection of the engine. ("United Airlines Flight 232," 1990)

The second factor that helped contribute to the crash of United flight 232 was: DC 10 hydraulic / flight control issues. After the debris damaged rear engine number two, it would severely affect the aircrafts hydraulics and flight controls. In this particular situation, the fragment from the damage piece to engine number two would spread debris into the hydraulics and flight control system of the aircraft. This would make controlling the plane more difficult, as the flight crew reported that the loss of power of the aircraft was one of the main reasons; why they conducting an emergency landing at Sioux City, Iowa. However, after the initial failure of engine number two the debris in the hydraulics and flight control system would essentially turn the aircraft into a runaway freight train. The loss of control made the landing more difficult, with the Captain reporting that they could not keep the nose level on the decent and that the plane would consistently veer to its right side. This veering, would place pressure on the right side of the aircraft, which would help contribute to the break up during plane after touching down. To combat this problem, the NTSB recommends that all aircraft have some type of back up flight control and hydraulics system. The presence of such a system could have helped to mitigate the effects of the disaster, by giving the pilots control of the aircraft. During the initial decent, this could have proven vital in ensuring that the pilots were able to successfully reach the runway at Sioux City and it helped to safely land the plane when it was initially touching down. ("United Airlines Flight 232," 1990)

A third issue that helped contribute to the crash of United flight 232 was: problems with the manufacture of engine. During their report, the NTSB found that the engine that was manufactured by GE helped contribute to the initial problems that were encountered. What happened was a titanium intake valve had a crack that could not be seen by the human eye. At the manufacturing facility, GE would perform an initial check for cracks and any kinds of defects during the middle of the manufacturing process, using ultrasonic along with macroetch technology. The problem is that the crack in the metal was developed during the final stage of the manufacturing process. This was the point where the two scans had already been conducted on the aircraft engine. As a result, this lack of quality control would help to create the initial problems that were experienced by the flight crew. ("United Airlines Flight 232," 1990)

To make matters worse, the NTSB found a number of other issues at GE that would help contribute to the problems with the engine the most notable would include: a lack of quality control and accurate record keeping. During numerous phases of the initial testing of the engine and its development there was a flaw that was detected. This was the crack that was found to have occurred at many points during the manufacturing process. Where, the company would use the different ultrasound and macroetch scanners to see if there were any issues with the titanium. The problem began with the fact that if a slight crack was overlooked, the constant heating and cooling that the metal, would cause the weakness to become more severe. As a result, because the company was not constantly scanning for this during the entire manufacturing process, meant that some engines would be shipped with the flaw. Then, the company did not accurately report the flaw that was discovered by engineers in various reports. This caused the supervisors and safety inspectors to not pay as close attention to the problem as they should have. To prevent the situation from becoming worse, the NTSB recommends that GE improve their overall monitoring and quality control. Where, they would use ultrasound and macro technology throughout the design as well as manufacturing process, to find any kind of structural weakness that could exist in the engine. Then, the company must improve their record keeping procedures for reporting structural flaws. This is significant because if the use of such technology had been place, the flaw in the titanium of the intake value would have been discovered. At which point, the company would more than likely would have corrected the problem before the engine would leave the manufacturing facility. The improved record keeping on the various flaws would have allowed managers, inspectors, regulators and the airlines to know that this is an issue that they must be made aware of. At which point, the chances that incidents such as United flight 232 would have been reduced. ("United Airlines Flight 232," 1990)

A fourth major issue that was identified was cabin safety. During the emergency landing, the procedures for infants and small children were unclear. Where, they would be strapped into the seat of airplane using the adult seat belt or they would sit on the lap of a passenger. This is problematic because during an emergency landing, these kinds of restraints or lack there of could contribute to problem, as these children / infants could go flying through the cabin of the aircraft during the confusion. At which point, the odds increase dramatically that the child / infant could have a severe fatality or they could injure other passengers. As a result, the NTSB recommends that all some sort of child safety procedure is designed to ensure that they are securely in their seats during the event of an emergency. ("United Airlines Flight 232," 1990)

A fifth area that helped make the situation on the ground worse was: the lack of coordination from first responders. In the NTSB report, the agency commends first responders for immediately going to scene within minutes of the emergency landing. However, the lack of coordination meant that the water truck would be slow to respond to the scene. Part of the reason for this was the difficulty in going through the corn stalks to reach the fuselage of the plane and the delay in sending the truck out to the scene. As a result, firefighters had less water available to extinguish the fire. This is significant because if the water truck had been available immediately after the accident, firefighters may have been more effective at containing the blaze. This could have meant that the overall number of causalities could have been reduced because EMTs would be able to access the plane quicker. To prevent this situation in the future, the NTSB recommends that first responders prepare for various incidents by conducting mock drills and have a response plan prepared for such events. ("United Airlines Flight 232," 1990)