TWA Flight 800 - Structural and Mechanical Factors Influenced the Accident - Case Study Example

TWA Flight 800 - Structural and Mechanical Factors Influenced the Accident Cause(s) of Accident On 17 July 1996, the TWA Flight 800, a twenty-five year-old Boeing exploded only 12 minutes, 51 seconds following its departure from JFK International Airport, New York. The explosion occurred over the Atlantic Ocean, about nine miles south of East Moriches on Long Island and all two hundred and thirty passengers in the Paris-bound model 747-131 plane died. In the history of American aviation, the subsequent National Transportation Safety Board (NTSB) inquiry was the most comprehensive and thorough.  However, the board never discovered any ultimate root of the explosion (Smith, 2010).   According to investigations, the tragedy resulted from an explosion in the plane’s central fuel tank. Numerous people theorize that the explosion resulted from a terrorist’s bomb or missile. Others believe that only a bomb could lead to an explosion powerful enough to bring down a plane as huge as a Boeing 747. Moreover, there were many resemblances of the incident to the bomb-caused Pan Am Flight 103 explosion. Furthermore, the plane had come from Hellenikon airport in Athens, Greece, reputable for poor security. The FBI also discovered on the plane’s remains PETN and RDX, chemical components of SEMTEX, the Czech plastic explosive, thereby increasing the suspicions of terrorism. Another group of people believes that someone must have shot down the plane. This is because the explosion took place over region W-105, a restricted martial area off Long Island coast where Navy training operations take place. A Navy vessel in this region could have therefore shot down the plane inadvertently. Eyewitnesses also claimed seeing a flash of light spurting towards the plane. Nonetheless, none of these beliefs is plausible enough – the cause of the explosion remains unclear and to date, researchers are still examining the plane’s salvaged parts as well as other comparable models in an attempt of seeking reasons for the explosion (Flanner, 2002 and FIRO, 1999). Structural and Mechanical Factors Upon close examination, the wreckage of the plane did not reveal any proof of pre-existing airplane structural faults, such as mechanical damage, corrosion or fatigue, which could have been contributors of the in-flight disintegration. Investigations revealed that the structure had minimal pre-existing corrosion damage, none of which could have affected or caused the airplane breakup. There were small fatigue cracks in some areas of the airplane, including in the floor beams’ shear ties and front spar stiffeners and in the lower chord of the front spar. Nevertheless, none of these cracks had united into a spreading crack that could have caused the in-flight breakup. Additionally, the joint connecting fuselage sections 41 and 42 on some 747s had been supposedly subject to manufacturing hitches but no proof existed to show that before the impact, it had separated in any spots (National Transportation Safety Board, 2000). Further suggestions indicated that the explosion could have been a result of the in-flight disjointing of the forward freight door. Nevertheless, all eight of the fastening cams alongside the base of the door as well as some bits of the freight door itself remained connected to the pins along the lower doorsill, and there was no sign of pre-impact breakdown of the hinge at the top of the door. This is an indication that the door was shut at impact. Additionally, fracture patterns and deformation on the door corresponded with the destruction of the adjoining fuselage structure, a confirmation of the fact that at the time of impact, the door had been closed. Consequently, the in-flight explosion of the plane was not the aftermath of a pre-existing condition resulting in decompression and a structural failure (National Transportation Safety Board, 2000). Sadly, the explosion caused the burning or damaging of most of the electrical wiring close to the central fuel tank this wiring therefore hampering the analysis of its role in instigating the explosion. Nevertheless, the NTBS was not left entirely unaware regarding sources of ignition. Two source theories that the NTBS tested were auto-ignition and electrical arcing (Flanner, 2002). Autoignition The Fuel Quantity Indicating System (FQIS) wires’ terminals in the planes’ central fuel tank could have been a possible source of ignition. Copper sulfide can accumulate here, a common phenomenon in old electrical systems, and that results from natural wiring deterioration. The accumulations can turn out to be causes of localized heat, which can pose as a threat due to auto-ignition. NTSB also believes that the plane’s faulty check valves and the scavenger pump could have caused auto-ignition in the central fuel tank. Officials believe that a transfer of fuel was taking place between tanks when the explosion took place, signifying that the scavenger pump, which is found in the central fuel tank, was functioning and its check valve could have been too tight. Thus, the valve may have permitted fuel only, and not vapor to go through it, and vapor may have been concentrated ion round the scavenger pump’s check valve of the. Compared to liquid fuel, the auto-ignition temperature of vapors is lower and the pump is a major energy source that can become too hot and lead to fuel vapor auto-ignition (National Transportation Safety Board, 2000). Electrical Arcing The NTSB also studied the condition of electrical wiring in similar plane models to detect whether a spark could take place in the central fuel tank. They found three-quarter inch layers of lint on wires and sharp metal shavings between and on wires in bundles, which can be ascribed to drilling. These shavings can remove insulation from the wires, exposing them and increasing the possibility of ignition. Exposed syrup-coated wires or wires coated with metallic drill shavings could be perilous since the two substances can be conductors, and can lead to an electrical arc, thereby igniting the fuel tank’s contents (Flanner, 2002). Contributing Factors Flanner (2002) explains that various factors could have raised the combustibility level of the contents of the plane’s central fuel tank. These include minimum ignition energy, fuel-air ratio, pressure, and temperature. According to the National Transportation Safety Board (2000), the central fuel tank of the plane was unusually hot, and could have been a major contributor of the explosion. On heating fuel, a larger percentage of the fuel exists as vapor, thereby raising the fuel-air ratio. One reason as to why the central fuel tank was so hot is that in Athens, the plane spent roughly four hours on the ground before leaving for Paris. Its air conditioners were left running for the four hours because of the summer heat and this period is uncommonly long. Paradoxically, since they are positioned directly beneath the central fuel tank and they do not drive cool air into it, the air conditioners warm the tank. The central fuel tank also had very little fuel and as such, little energy was needed to heat it up. Research indicates that if the tank were full, it would have heated at a slower rate. Pressure/altitude also has an effect on the fuel-air ratio – more fuel evaporates with an increase in altitude because of declining ambient pressure. Fuel-air ratio consequently augments with rising altitude. The least amount of temperature required to kindle the fuel reduces with increased altitude. The lowest amount flammability heat at 13,800 feet is roughly 26°C, quite below 46°C, which was the reported temperature in the plane’s central fuel tank. Therefore, a combination of pressure, temperature, ignition energy, and the fuel-air ratio on the plane generate a distinctive environment that was highly favorable to the outburst (Flanner, 2002). Investigation Board Findings The most probable causes of the plane’s explosion were the existence of both a combustible substance and an ignition source. Other findings included the fact that during the accident, there were scattered clouds and light winds, but no major meteorological circumstances that could have interfered with the flight. In addition, the plane was prepared, certificated, and dispatched compliant with Federal regulations and approved Trans World Airlines (TWA) procedures. Moreover, it was found that at the time of the accident, the fuel/air vapor in the ullage of the center-wing fuel tank of the plane was combustible and that the air/fuel explosion in the plane’s center-wing fuel tank was capable of creating adequate internal pressure to shatter the tank apart (National Transportation Safety Board, 2000). Another finding was that running transport-category aircrafts with a mixture of combustible air/fuel in fuel tanks poses a preventable threat of explosion, and deposits silver-sulfide on FQIS components within fuel tanks presents the threat of the explosion of combustible air/fuel vapor. Moreover, it is very improbable that the combustible air/fuel vapor in the aircraft’s center wing fuel tank caught fire because of a missile fragment; static electricity; a meteor or lightning strike; or a minute volatile charge placed on the CWT. Other unlikely causes include a fire moving from a different fuel tank through the vent to the CWT system; hot surface or auto ignition, arising from high temperatures generated by sources that are external to the CWT; a faulty CWT scavenge pump; a faulty CWT jettison pump; or an uncontrolled engine breakdown (National Transportation Safety Board, 2000). Recommendations Minimizing Ignition Sources There is need to inspect a plane’s wiring regularly in order to identify and fix the accumulation of copper sulfide on Fuel Quantity Indicating System (FQIS) terminals that can generate auto-ignition, and to identify and fix stripped insulation that can cause arcing. The installation of a more resilient insulation covering electrical wiring in old and new commercial airlines would also decrease the danger of arcing. Another recommendation is on the need to keep the environment of the central fuel tank clean in order to avert the accumulation of such potential conducting instruments as syrup and drill shavings. Additionally, inspectors should inspect localized sources of heat and check valves in the scavenger pump. As far as safety is concerned, in addition to identifying sources of ignition, it is also good to minimize the central fuel tanks contents’ combustibility (Flanner, 2002). Temperature Reduction Temperature should be kept low in order to maintain a low fuel-air ratio in central fuel tanks of planes. Air conditioning units present the major heating source and adding effective insulation between the central fuel tank and air conditioners is of great importance in reducing the transfer of heat to the central fuel tank. Heat can also be reduced by reducing the amount of time the air conditioners are functioning when the plane is on land. Finally, heat in the central fuel tank can be reduced by maintaining a large amount of fuel in the tank, which would require a greater quantity of energy to heat. Thus, heating occurs more gradually (National Transportation Safety Board, 2000). Fuel The nature of the fuel in the tank is a crucial factor of combustibility. Even though fuel-air ratios of various fuels may be similar, their flashpoints will be dissimilar. Therefore, using a fuel with a higher flashpoint, such as JP-5, is one way of decreasing the threat of combustion. Mid-air fuel explosions can be eliminated using a fuel that does not ignite easily (Flanner, 2002). Outcomes Following the accident, NTSB ordered the Unites States Federal Aviation Administration to ensure that airlines take precautions of decreasing the dangers of similar fuel tank explosions. They were supposed to make aircraft design changes as well as change their operating procedures immediately in order to prevent future incidences. However, this is a very costly undertaking that would take a long time and to date, some of these changes have not been implemented – according to an industry group directed by Boeing and Airbus, eradicating the problem leading to the explosion would cost more than the harm that future similar explosions would cause. However, the aviation industry has already is taken steps to reduce prospective fuel-tank explosions, and it has been able to reduce the prospect of explosions from once every four years to once every sixteen years (Grimaldi, 1998). Boeing and Airbus officials have also developed other safety enhancement mechanisms such as an assertive program of examining aircraft and fixing prospective electrical hitches that could cause explosions. The Federal Aviation Administration also require that new commercial airplanes be designed and constructed in such a way that center fuel tanks are in a volatile condition during no more than 7% of their period of operation, including when the planes are on the ground. The aircrafts’ fuel-air mixture was previously explosive roughly 30% of the time (Grimaldi, 1998). References FIRO (1999). Anomalies within the Official Crash Investigation of TWA Flight 800. Retrieved from http://flight800.org/sub_rep.htm Flanner, M. (2002). An Analysis of the Central Fuel Tank Explosion of TWA Flight 800. Retrieved from http://elvis.engr.wisc.edu/uer/uer00/author2/content.html Grimaldi, J. V. (1998). Twa Flight 800/Two Years Later – Preventing Jet Explosions Too Costly, Industry Says – Aviation Group Backs Only Some Of Ntsb's Proposed Safety Fixes. Retrieved from http://community.seattletimes.nwsource.com/archive/?date=19980716&slug=2761501 National Transportation Safety Board. (2000). In-flight breakup over the Atlantic Ocean, Trans World Airlines Flight 800 Boeing 747-131, N93119, near East Moriches, New York, July 17, 1996. Darby, PA: DIANE Publishing. Smith, S. J. (2010). TWA Flight 800 Analysis. Retrieved from http://www.whale.to/b/twa_flight_800_analysis.html Read More