Submitted to the Worldwide Campus in Partial Fulfillment of the Requirements of
ASCI 612
Embry-Riddle Aeronautical University
Worldwide Campus
Worldwide Online
June 2010
Introduction
The Sioux City, Iowa crash of United Airlines Flight 232 was a classic case of engine design failure. This accident was as significant for propulsion engineers as the Aloha accident was for structural engineers. This accident crossed a variety of disciplines and served to show how the interaction between system components affected the probability of an accident. The Sioux City accident had very clearly defined precursors and paradigms in its design and certification that failed to work as intended. In addition, this accident illustrates how a lack of an airplane system design perspective during the conception and design phase can have unintended, catastrophic consequences. This case study was selected because it supports the topics covered in Chapter 3 and 8 of the "Occupational Safety and Health" book.
The Flight
It was a routinely scheduled DC-10 passenger flight form Denver, Colorado to Philadelphia, Pennsylvania with a lay over in Chicago, Illinois; United Airlines Flight 232 departed Colorado’s Stapleton International Airport on July 19, 1989. With 285 passengers aboard and 11 crew members the flight progressed without any complications. After about an hour into the flight one of the crew members heard a loud noise followed by an irregular movement in the aircraft. The crew then noticed that they had lost all indications on the number two engine. A comprehensive search was devised to locate the source of the problem. When they had determined that it was in fact the number two engine they proceeded to comply with the appropriate engine shutdown procedures. When they finally completed the shutdown the flight engineer noticed that they lost all of the fluid to the number 3 hydraulic system, an indication that there had to be a severed line of some sort (Air Disaster, n.d.). This problem became a serious concern because the aircraft’s flight controls depend upon a total of 142.6 us gallons of hydraulic fluid and constant pressure of 3000 PSI in all three systems (NTSB, 1992). Shortly after loss of hydraulic fluid the aircraft began an un-commanded right turn which the first officer attempted to correct but his movements where unsuccessful. In an attempt to regain some hydraulic pressure the crew deployed an emergency device know as an Air Driven Generator (ADG). When the ADG was deployed it employed an emergency power source to the right emergency AC bus Tie Relay. This provided the necessary electrical power to operate their electrical auxiliary hydraulic pump (NTSB, 1992).
The attempt to restore hydraulic pressure was unsuccessful so they declared an in-flight emergency and requested an emergency landing site to Minneapolis, Minnesota’s Air Traffic Control (ATC). ATC notified the crew that the nearest landing location would be Des Moines International Airport only to retract his statement a few moments later with a new landing location at Sioux City, Iowa (Air Disaster, n.d.). The crew realized that a forced landing had to be accomplished in order to land this plane. Preparation for the landing began by jettisoning extra fuel from the aircraft and lowering the landing gear by the alternative extension method. Visual contact was made with the runway at approximately 9 miles out. The runway that ATC intended the aircraft to land on runway 31 which was 8,999 feet long at a magnetic heading of 310 degrees, but the aircrafts relative position to the runway, suggested a more viable landing could be accomplished on runway 22 which was 6,600 feet long (NTSB, 1992). The runway chosen presented many problems, the first fact was that the runway was shorter than the initial runway chosen and also that it had been closed for maintenance. Upon entering final
