Sioux City Crash INTRODUCTION Aircraft accidents can be a tragic thing. Some people may argue that all are avoidable. But when considering this statement, one must always remember there is an element that is in all accidents.
Humans. Either through design, being flown by, or maintained by, humans are in all aspects of flying.As long as humans are in 100% control of an airplane there will be accidents. However, a good side to an accident is it is thoroughly researched by the NTSB. (National transportation and safety board). From a majority of those accidents, something can benefit aviation in general.
Aviation can be benefited through design, training, or in this situation, re-evaluating current limitations to a safer level. The focus of my project is going to be on a particular accident that took place on July 19, 1989 when a McDonnell Douglas DC-10-10 aircraft crashed in Sioux City, Iowa.This particular type of aircraft, at the time of the accident, had been in production for about 18 years. The United Airlines jet was bound for Chicago when the tail-mounted engine broke apart and severed the aircrafts main hydraulic lines. Without hydraulics the aircraft wouldn’t be able to maneuver. It would also have trouble slowing down for landing. This meant trouble for United Airlines flight 232 with 285 passengers and 11 crew- members on board. Statement of the Problem: A potential problem of complete hydraulic failure if the tail-mounted engine breaks apart.
PAGE 1 Hypothesis Statement: My theory is this all could have been avoided. The actions taken after the accident could have been incorporated in the initial design of the aircraft. RESULTS On July 19,1989 a United Airlines DC-10-10 passenger plane took off Stapleton International in Denver Colorado. The plane was scheduled to make a quick stop in Chicago, Illinois and then continue on to Philadelphia, PA. After an uneventful hour of flight a loud thump was heard, followed by a shaking of the aircraft.The flight crew observed the tail-mounted engine had failed.
(SEE FIGURE 3) While performing an engine shutdown procedure, the crew noticed that they didn’t have any hydraulic pressure. They also noticed that the fluid level was at zero. The co-pilot tried to maneuver the airplane with no success. The crew then radioed to the air traffic controller that they needed emergency assistance to the nearest airport.Sioux City, Iowa was found to be the almost straight-ahead.
The captain then briefed the passengers of the up-coming trials. It just so happen that there was a United Airlines DC-10 pilot instructor sitting in first class. He asked if he could be of any assistance and the captain asked him to see if there was any damage that the could see. The instructor found that the flight controls on the wings weren’t moving and that the horizontal stabilizer had damage to the left and right side.
The horizontal stabilizer is the part of the aircraft that controls elevation and what is known as yaw. (Right and left turning) Now that they definitely knew they didn’t have any flight controls the crew began to discuss what ways the aircraft could be maneuvered. PAGE 2 The instructor pilot recommended the use of engine power to maneuver the airplane. The idea seemed to work and being that all other options were few, the crew adopted this plan of action. When flight 232 was about eight miles from the airport they lowered the landing gear.To their dismay they learned from the air traffic controller that they were lined up on a runway that was closed for repairs.
The captain elected to stay on course because of the difficulty to turn the airplane. The air traffic controller said that the runway was 3000 feet shorter but they shouldn’t have any trouble landing due to the repairs. During the final approach the flight crew felt they were on course to make the landing. However they were a little faster than normal, due to not being able to lower the proper flight controls known as the flaps and slats. These two controls allow the airplane to fly at a lower speed.At about a hundred feet above the ground, the pilot reported that the nose dipped considerably and the right wing dropped also. Both pilots called for a reduction of power but the instructor pilot said that he needed to continue using the engine power to try and control the decent.
The airplanes right wing tip was the first to touch the runway, followed by the right main landing gear. Eyewitness accounts said the airplane ignited and cart wheeled upon impact. In all 111 people died. The remaining 155 people escaped with recoverable injuries. The National Transportation and Safety Board (NTSB) now needed to know why the accident occurred.
They transported the tail section parts to a nearby hangar and began to PAGE 3 reconstruct the tail. Using wood trestles they reconstructed the tail section. Upon completion the puzzle was starting to piece together. The left side of the horizontal stabilizer showed no damage that could have cause the crash. (See figure 2) However, the right side was a different story.When the tail mounted engine failed, parts from it cut through the aircraft skin and severed the number 3 and number 2 hydraulic system lines. The next phase of the investigation was now focused on why the engine failed.
But there was a problem. They couldn’t find the front section of the engine. It wasn’t until three months later in a cornfield in Alta, Iowa, the section was found.Alta is about 35 miles away from the crash site. Figure 1 shows the reconstructed blades. Further examination of the blades showed two things. One, there was a fatigue crack on one of the blades which went undetected at a previous maintence inspection.
Two, the fatigue crack was the result of poor manufacturing processes. Finally, something had to be done to assure this type of situation wouldn’t happen again.The NTSB determined that United Airlines had failed in giving adequate consideration to human factors which resulted in the failure to detect the crack. McDonnell Douglas was asked to come up with something to ensure, given the same circumstances, that this wouldn’t happen again. Three months after the accident McDonnell Douglas announced the development of design enhancements. The enhancement consisted of three things. One, an electrically operated shutoff valve that would close if fluid levels dropped below a preset limit in the main hydraulic system.Two, a sensor to detect the fluid loss and a light in the cockpit to alert the crew.
PAGE 4 FIG 1 FIG 2. PAGE 5 FIG 3 DISCUSSION Looking at this accident from a distance it shows many remarkable things. What are the odds of a United Airlines Instructor pilot for the DC-10 being on the flight when he is needed the most. The way the crew pulled together to come up with a plan of how they were going to land is absolutely remarkable. However there is more to this story if one looks closer.To examine the flight crew’s actions would be unfair.
The crew did the best job they could given the circumstances. In fact, the exact scenario was given to pilots in the simulator and not one of them could come close to landing the airplane. So for this reason the NTSB’s findings are going to be examined.
PAGE 6 When the tail was reconstructed this showed the inspectors a lot. They already knew the engine had failed.But they wanted to know why the hydraulic failure. The left side had some holes but nothing large enough to cause the accident.
The right side was a different story. When aircraft engines turn they turn clockwise. Thus if something were to happen to the blades, like in this case, they wouldn’t go to the left.
They would go to where the momentum is carrying them. The blades went through the engine compartment and on to the elevator section, which cut the hydraulic lines. (See fig 2) The engine examination was tougher than the tail section. If you have ever tried to put something back together and not have all the pieces, the task is almost impossible. The front section was that missing piece.It was found three months later in Alta, Iowa. This location is where flight 232 experienced the engine failure. Imagine seeing something like Fig 3 falling from 20,000 feet.
Upon complete examination it was found that there was weakness in the metal of the blades, which was incorporated when it was made. Over time the crack grew. It took the blades nearly 17,000 hours to finally give way.This should have been detected due to the fact that maintainers frequently examine these blades. Granted the cracks aren’t visible with the naked eye but process known as FPI (field penetrates inspection) is done. In this process the blades are coated with a florescent die and after the dye has dried a florescent light is used and the blades are scanned.
Cracks will show up under the light. This exact process was done approximately four months prior to the accident.The crack wasn’t detected. Page 7 One might say that the engine compartment should contain an engine failure. This is true, but this particular engine compartment wasn’t designed to contain a failure of this magnitude.
CONCLUSIONS As a result of the research and analysis conducted, the following conclusions were developed. First is the issue of United Airlines maintenance practices.If the maintenance workers had done their job properly they would have found the crack long before the accident. Which may have solved the whole problem and it may have never occurred in the first place. One doesn’t know. One might wonder why this wasn’t considered in the design initially. However engineers cant predict every mechanical failure.
If they did and put extra parts in for just in case reasons, then the aircraft would have a lot more parts. Which means more maintenance. Which means more cost to the customer for repairs. As stated in the hypothesis statement, this all could have been avoided.
If the precautions taken after the accident would have been in the initial design complete hydraulic failure would have been virtually impossible. Thus, if the same scenario happened the plane wouldn’t lose hydraulic power.REFERENCES NTSB. [No date] United Airlines Flt 232 McDonnell Douglas D-10-10 Sioux Gateway Airport Sioux City, Iowa. Available: [online] www.web.pr.erau.edu/library /ntsbreports/ntsb9006.html [10-25-00] Religoustolerance.org [no date] Apa Format (American Psychological Association) Available: [online] www.religioustolerance.org/int cita.htm [11-13-00] Page 8 Aviation Essays.