National Transportation Safety Board - Case Study Example

National Transportation Safety Board Cause(s) of Accident American Airlines Flight 191 was a passenger flight that was regularly scheduled from O’Hare International Airport in Chicago to Los Angeles International Airport (Kilroy, 2012). It was involved in an accident on May 25, 1979 and killed all the 258 passengers on board and 13 crew, as well as two people on the ground. The National Transportation Safety Board (NTSB) took the responsibility of determining the probable causes of the accident and made recommendations to prevent future incidences (National Transportation Safety Board, 1979). The investigation into the accident by the NTSB revealed that the probable cause of the accident was the asymmetrical stall and the aircraft’s ensuing roll due to the uncommanded retraction of the lift wing outboard that led to the edge slats and the loss of the slat disagreement and stall warning indication systems (Aviation Safety Network, 2012). This occurrence resulted from maintenance-induced damage that led to the separation of the pylon assembly procedures and number one engine, which eventually led to the pylon structure’s failure (Vatz, 2003). Structural and Mechanical Factors This accident was mainly a result of structural and mechanical factors. Investigations by the NTSB revealed that when the engine separated because of the asymmetrical stall and the aircraft’s ensuing roll, it disabled the control panel of the Captain. The Captain’s control panel contained both systems of slat disagreement (National Transportation Safety Board, 1979). The separation of the pylon assembly procedures and the number one engine, which ultimately resulted to the failure of the pylon structure, are all structural and mechanical aspects of aircrafts. The severed hydraulic lines allowed the slats on the aircraft’s left wing to retract gradually and the stall speed on the aircraft’s left wing rose significantly (Vatz, 2003). When it slowed through 164 knots, left wing aerodynamically stalled because of its clean configuration. This happened while the right wing continued to generate lift with its slats still in the position of takeoff. Since one wing was stalling and the other was producing lift, the aircraft ultimately rolled past a 90 degrees bank, and crashed to the ground (Kilroy, 2012). Contributing Factors While structural and mechanical factors were the main cause of the accident, investigations revealed that there were factors that contributed to the accident of American Airlines Flight 191 (Aviation Safety Network, 2012). Report by NTSB reveals that the vulnerability of the pylon attaches points design to maintenance damage contributed to the accident. The investigation found out that another factor contributing to the accident was the vulnerability of the leading edge slat system design to the damage that produced asymmetry. In addition, complacency and deficiencies in Federal Aviation Administration (FAA) reporting and surveillance systems that failed in detecting and preventing the use of improper maintenance procedures contributed to the accident. Besides deficiencies in the communications and practices among the FAA, the manufacturer and operators contributed to the accident because they failed to determine and disseminate the particulars about past maintenance damage incidents. Lastly, the intolerance of prescribed operational procedures to this kind of emergency that was unique contributed to the accident (Vatz, 2003). Investigation Board Findings Following its investigations, the National Transportation Safety Board came up with a number of key findings. The first finding was that either the pylon and engine assembly separated at or immediately after the aircraft’s liftoff and that the flight crew was committed to continue with the takeoff (National Transportation Safety Board, 1979). Secondly, the investigation board found out that the structural separation of the pylon was due to the complete failure of the aft bulkhead’s forward flange after its residual strength had been reduced critically by the fracture, as well as subsequent service life (Kilroy, 2012). The investigation board also determined that the fatigue cracking and overload fracture on the pylon aft bulkheads happened to be the only preexisting damage on the bulkhead. In addition, it was found out that the flight crew flew the aircraft according to the emergency procedure already prescribed, which called for the flying of climb out at V2 speed. Another key finding by the investigation board was that during DC-10 certification, there was no consideration of the engine pylon’s structural separation (Aviation Safety Network, 2012). Recommendations Following the accident, the NTSB made numerous recommendations. To start with, the board recommended that the FAA should immediately issue an emergency Airworthiness Directive for the inspections of pylon attach points on DC-10 aircraft by approved inspection methods. It also recommended that FAA should ensure that the design of aircraft transport category provides positive protection against asymmetry of lifts during phases of flight that are critical (Vatz, 2003). The NTSB further recommended that FAA should issue a Maintenance Alert Bulletin directing its maintenance inspectors to advise their assigned carriers to discontinue the practice of raising and lowering the pylon while the engine is still attached. Furthermore, the NTSB recommended that FAA, when incorporating certification procedures, should see to it that possible failure combinations that can be caused by primary structural damage in areas where critical systems are routed; and consider factors that affect aircraft’s maintainability such as redundant or positive retention of connecting hardware and accessibility for inspection (National Transportation Safety Board, 1979). Outcomes After the accident, a number of positive outcomes were recorded in the aviation industry in the United States and other parts of the world. FAA, manufacturers of aircrafts, together with the airline companies enhanced their safety and maintenance programs with the view of preventing accidents of the same nature in the future. In addition, they initiated and continued comprehensive and strict surveillance efforts aimed at improving the quality of control programs and assure full compliance with the process and manufacturing specifications (Kilroy, 2012). Most of the investigation board recommendations were implemented and this is evidenced by the fact that an accident of the same nature has never occurred since then. In particular, aviation regulators, manufacturers, and companies followed virtually all the recommendations that were aimed at enhancing safety and quality maintenance in the aviation industry to avert the occurrence of accidents (Aviation Safety Network, 2012). While several accidents have happened since then, the recommendations proved to be instrumental in enhancing the aviation industry’s safety. References Aviation Safety Network. (2012). American Airlines Flight 191. Retrieved on 19 September, 2012 from http://aviation-safety.net/database/record.php?id=19790525-2 Kilroy, C. (2012). Special Report - American Airlines Flight 191. Retrieved on 19 September, 2012 from http://www.airdisaster.com/special/special-aa191.shtml National Transportation Safety Board. (1979). NTSB Aircraft Accident Report - American Airlines Flight 191. Retrieved on 19 September, 2012 from http://www.airdisaster.com/reports/ntsb/AAR79-17.pdf Vatz, M. (2003). Knowing When to Stop: The Investigation of Flight 191. Retrieved on 19 September, 2012 from http://dspace.mit.edu/bitstream/handle/1721.1/39430/59008054.pdf?sequence=1 Read More