Analysis of reported witness observations
At the start of FBI's investigation, because of the possibility that international terrorists might have been involved, assistance was requested from the Central Intelligence Agency (CIA). CIA analysts, relying on sound-propagation analysis, concluded that the witnesses could not be describing a missile approaching an intact aircraft, but were seeing a trail of burning fuel coming from the aircraft after the initial explosion. This conclusion was reached after calculating how long the sound of the initial explosion took to reach the witnesses, and using that to correlate the witness observations with the accident sequence. In all cases, the witnesses could not be describing a missile approaching an intact aircraft, as the plane had already exploded before their observations began.
As the investigation progressed, the NTSB decided to form a witness group to more fully address the accounts of witnesses. From November 1996 through April 1997, this group reviewed summaries of witness accounts on loan from the FBI (with personal information redacted), and conducted interviews with crew-members from a New York Air National Guard HH-60 helicopter and C-130 airplane, as well as a U.S. Navy P-3 airplane that was flying in the vicinity of TWA 800 at the time of the accident.
In February 1998, the FBI, having closed its active investigation, agreed to fully release the witness summaries to the NTSB. With access to these documents no longer controlled by the FBI, the NTSB formed a second witness group to review the documents. Because of time that had elapsed (about 21 months) before the NTSB received information about the identity of the witnesses, the witness group chose not to reinterview the witnesses, but instead to rely on the original summaries of witness statements written by FBI agents as the best available evidence of the observations initially reported by the witnesses. Despite the two and a half years that had elapsed since the accident, the witness group did interview the captain of Eastwind Airlines Flight 507, who was the first to report the explosion of TWA 800, because of his vantage point and experience as an airline pilot.
The NTSB's review of the released witness documents determined that they contained 736 witness accounts, of which 258 were characterized as "streak of light" witnesses ("an object moving in the sky... variously described [as] a point of light, fireworks, a flare, a shooting star, or something similar.") The NTSB witness group concluded that the streak of light reported by witnesses might have been the actual airplane during some stage of its flight before the fireball developed, noting that most of the 258 streak-of-light accounts were generally consistent with the calculated flight-path of the accident airplane after the CWT explosion.
Thirty-eight witnesses described a streak of light that ascended vertically, or nearly so, and these accounts "seem[ed] to be inconsistent with the accident airplane's flight-path." In addition, 18 witnesses reported seeing a streak of light that originated at the surface, or the horizon, which did not "appear to be consistent with the airplane's calculated flightpath and other known aspects of the accident sequence." Regarding these differing accounts, the NTSB noted that based on their experience in previous investigations "witness reports are often inconsistent with the known facts or with other witnesses' reports of the same events." The interviews conducted by the FBI focused on the possibility of a missile attack; suggested interview questions given to FBI agents such as "Where was the sun in relation to the aircraft and the missile launch point?" and "How long did the missile fly?" could have biased interviewees' responses in some cases. The NTSB concluded that given the large number of witnesses in this case, they "did not expect all of the documented witness observations to be consistent with one another" and "did not view these apparently anomalous witness reports as persuasive evidence that some witnesses might have observed a missile."
After missile visibility tests were conducted in April 2000, at Eglin Air Force Base, Fort Walton Beach, Florida, the NTSB determined that if witnesses had observed a missile attack, they would have seen:
a light from the burning missile motor ascending very rapidly and steeply for about 8 seconds
the light disappearing for up to 7 seconds
upon the missile striking the aircraft and igniting the CWT, another light, moving considerably more slowly and more laterally than the first, for about 30 seconds
this light descending while simultaneously developing into a fireball falling toward the ocean None of the witness documents described such a scenario.
Because of their unique vantage points or the level of precision and detail provided in their accounts, five witness accounts generated special interest: the pilot of Eastwind Airlines Flight 507, the crew members in the HH-60 helicopter, a streak-of-light witness aboard US Airways Flight 217, a land witness on the Beach Lane Bridge in Westhampton Beach, New York, and a witness on a boat near Great Gun Beach. Advocates of a missile-attack scenario asserted that some of these witnesses observed a missile; analysis demonstrated that the observations were not consistent with a missile attack on TWA 800, but instead were consistent with these witnesses having observed part of the in-flight fire and breakup sequence after the CWT explosion.
The NTSB concluded, "the witness observations of a streak of light were not related to a missile and that the streak of light reported by most of these witnesses was burning fuel from the accident airplane in crippled flight during some portion of the post-explosion, preimpact breakup sequence". The NTSB further concluded, "the witnesses' observations of one or more fireballs were of the airplane's burning wreckage falling toward the ocean".
Possible ignition sources of the center wing fuel tank
To determine what ignited the flammable fuel-air vapor in the CWT and caused the explosion, the NTSB evaluated numerous potential ignition sources. All but one were considered very unlikely to have been the source of ignition.
Missile fragment or small explosive charge
Although the NTSB had already reached the conclusion that a missile strike did not cause the structural failure of the airplane, the possibility that a missile could have exploded close enough to TWA 800 for a missile fragment to have entered the CWT and ignited the fuel/air vapor, yet far enough away not to have left any damage characteristic of a missile strike, was considered. Computer simulations using missile performance data simulated a missile detonating in a location such that a fragment from the warhead could penetrate the CWT. Based on these simulations, the NTSB concluded that it was "very unlikely" that a warhead could have detonated in such a location where a fragment could penetrate the CWT without other missile fragments impacting the surrounding airplane structure, leaving distinctive impact marks.
Similarly, the investigation considered the possibility that a small explosive charge placed on the CWT could have been the ignition source. Testing by the NTSB and the British Defence Evaluation and Research Agency demonstrated that when metal of the same type and thickness of the CWT was penetrated by a small charge, petalling of the surface occurred where the charge was placed, with pitting on the adjacent surfaces, and visible hot-gas washing damage in the surrounding area. Since none of the recovered CWT wreckage exhibited these damage characteristics, and none of the areas of missing wreckage was large enough to encompass all the expected damage, the investigation concluded that this scenario was "very unlikely".
Other potential sources
The NTSB also investigated whether the fuel-air mixture in the CWT could have been ignited by lightning strike, meteor strike, auto ignition or hot surface ignition, a fire migrating to the CWT from another fuel tank via the vent system, an uncontained engine failure, a turbine burst in the air conditioning packs beneath the CWT, a malfunctioning CWT jettison/override pump, a malfunctioning CWT scavenger pump, or static electricity. After analysis, the investigation determined that these potential sources were "very unlikely" to have been the source of ignition.
Fuel quantity indication system
Because a combustible fuel-air mixture will always exist in fuel tanks, Boeing designers had attempted to eliminate all possible sources of ignition in the 747's tanks. To do so, all devices are protected from vapor intrusion, and voltages and currents used by the fuel quantity indication system (FQIS) are kept very low. In the case of the 747-100 series, the only wiring located inside the CWT is that associated with the FQIS.
For the FQIS to have been Flight 800's ignition source, a transfer of higher-than-normal voltage to the FQIS would have needed to occur, as well as some mechanism whereby the excess energy was released by the FQIS wiring into the CWT. The NTSB concluded, "the ignition energy for the CWT explosion most likely entered the CWT through the FQIS wiring."
Though the FQIS itself was designed to prevent danger by minimizing voltages and currents, the innermost tube of Flight 800's FQIS compensator showed damage similar to that of the compensator tube identified as the ignition source for the surge tank fire that destroyed a 747 near Madrid in 1976. This was not considered proof of a source of ignition. Evidence of arcing was found in a wire bundle that included FQIS wiring connecting to the center wing tank. Arcing signs were also seen on two wires sharing a cable raceway with FQIS wiring at station 955.
The captain's CVR channel showed two "dropouts" of background power harmonics in the second before the recording ended (with the separation of the nose). This might well be the signature of an arc on cockpit wiring adjacent to the FQIS wiring. The captain commented on the "crazy" readings of the number 4 engine fuel flow gauge about 2 1/2 minutes before the CVR recording ended. Finally, the CWT fuel quantity gauge was recovered and indicated 640 pounds instead of the 300 pounds that had been loaded into that tank. Experiments showed that applying power to a wire leading to the fuel quantity gauge can cause the digital display to change by several hundred pounds before the circuit breaker trips. Thus, the gauge anomaly could have been caused by a short to the FQIS wiring. The NTSB concluded that the most likely source of sufficient voltage to cause ignition was a short from damaged wiring, or within electrical components of the FQIS. As not all components and wiring were recovered, pinpointing the source of the necessary voltage was not possible.
Report conclusions
The NTSB investigation ended with the adoption of the board's final report on August 23, 2000. The board determined that the probable cause of the TWA 800 accident was:
[An] explosion of the center wing fuel tank (CWT), resulting from ignition of the flammable fuel/air mixture in the tank. The source of ignition energy for the explosion could not be determined with certainty, but, of the sources evaluated by the investigation, the most likely was a short circuit outside of the CWT that allowed excessive voltage to enter it through electrical wiring associated with the fuel quantity indication system.
In addition to the probable cause, the NTSB found the following contributing factors to the accident:
The design and certification concept that fuel tank explosions could be prevented solely by precluding all ignition sources.
The certification of the Boeing 747 with heat sources located beneath the CWT with no means to reduce the heat transferred into the CWT or to render the fuel tank vapor noncombustible
During the course of its investigation, and in its final report, the NTSB issued 15 safety recommendations, mostly covering fuel tank and wiring-related issues. Among the recommendations was that significant consideration should be given to the development of modifications such as nitrogen-inerting systems for new airplane designs, and where feasible, for existing airplanes.
Controversy
The NTSB's conclusions about the cause of the TWA 800 disaster took four years and one month to be published. The FBI's earliest investigations and interviews, later used by the NTSB, were performed under the assumption of a missile attack, a fact noted in the NTSB's final report. Six months into the investigation, the NTSB's chairman, Jim Hall, was quoted as saying, "All three theories—a bomb, a missile, or mechanical failure—remain." Speculation was fueled in part by early descriptions, visuals, and eyewitness accounts of the disaster that indicated a sudden explosion and trails of fire moving in an upward direction.
On June 19, 2013, the NTSB acknowledged in a press release that they received a petition for reconsideration of its investigation into the July 17, 1996, crash of TWA Flight 800. In 2014, the NTSB declined the petition to reopen the investigation. In a press release, the NTSB stated: "After a thorough review of all the information provided by the petitioners, the NTSB denied the petition in its entirety because the evidence and analysis presented did not show the original findings were incorrect."
Aftermath
Many internet users responded to the incident; the resulting web traffic set records for internet activity at the time. CNN's traffic quadrupled to 3.9 million views per day. The website of The New York Times had its traffic increase to 1.5 million views per day, 50% higher than its previous rate. In 1996, few U.S. government websites were updated daily, but the United States Navy's crash website was constantly updated and had detailed information about the salvage of the crash site.
The wreckage was moved to an NTSB facility in Ashburn, Virginia, that was custom-built for the purpose. The reconstructed aircraft was used to train accident investigators until it was decommissioned in 2021.
On July 18, 2008, the U.S secretary of transportation visited the facility and announced a final rule designed to prevent accidents caused by fuel-tank explosions. The rule required airlines to pump inert gas into the tanks. The rule covered the CWT on all new passenger and cargo airliners, and passenger planes built in most of the 1990s, but not old cargo planes. The NTSB had first recommended such a rule just five months after the incident and 33 years after a similar recommendation issued by the Civil Aeronautics Board Bureau of Safety on December 17, 1963, nine days after the crash of Pan Am Flight 214.
The crash of TWA Flight 800, and that of ValuJet Flight 592 earlier in 1996, prompted Congress to pass the Aviation Disaster Family Assistance Act of 1996 as part of the federal aviation appropriations bill. Among other things, the act gives NTSB, instead of the particular airline involved, responsibility for coordinating services to the families of victims of fatal aircraft accidents in the United States. In addition, it restricts lawyers and other parties from contacting family members within 30 days of the accident.
During the investigation, the NTSB and the FBI clashed with each other. The agencies lacked a detailed protocol describing which agency should take the lead when whether an event was an accident or a criminal act was initially unclear. At the time of the crash, 49 CFR 831.5 specified that the NTSB's aviation accident investigations have priority over all other federal investigations. After the TWA flight 800 investigation, the NTSB recognized the need for better clarity. The NTSB sought and secured language to clarify the issue in 49 USC 1131(a)(2)(B), which was amended in 2000 to read:
If the Attorney General, in consultation with the Chairman of the [NTSB], determines and notifies the [NTSB] that circumstances reasonably indicate that the accident may have been caused by an intentional criminal act, the [NTSB] shall relinquish investigative priority to the [FBI]. The relinquishment of investigative priority by the [NTSB] shall not otherwise affect the authority of the [NTSB] to continue its investigation under this section
49 USC 1131(a)(2)(B)
In 2005, the NTSB and the FBI entered into a memorandum of understanding (MOU) that states that, "[i]n the immediate aftermath of a transportation accident, the NTSB is the presumptive lead investigative agency and will assume control of the accident scene." The FBI may still conduct a criminal investigation, but the NTSB investigation has priority. When investigative priority remains with the NTSB, the FBI must coordinate its investigative activities with the NTSB investigator-in-charge. This authority includes interviewing witnesses. The MOU states that: “[t]his procedure is intended…to ensure that neither NTSB nor FBI investigative activity unnecessarily complicates or compromises the other agency’s investigation. The new statutory language and the MOU have improved coordination between the NTSB and FBI since the TWA flight 800 accident.” As of 2005, NTSB and FBI personnel conduct joint exercises. Each agency can call upon the other's laboratories and other assets. The NTSB and the FBI have designated liaisons to ensure that information flows between agencies, and to coordinate on-scene operations.
Heidi Snow, the fiancée of Flight 800 victim Michel Breistroff, established the AirCraft Casualty Emotional Support Services nonprofit group together with families of victims of Pan Am Flight 103.[69]
Memorials
TWA Memorial
The TWA Flight 800 International Memorial was dedicated in a 2-acre (8,100 m2) parcel immediately adjoining the main pavilion at Smith Point County Park in Shirley, New York, on July 14, 2004. Funds for the memorial were raised by the Families of TWA Flight 800 Association. The memorial includes landscaped grounds, flags from the 13 countries of the victims, and a curved Cambrian Black granite memorial with the names engraved on one side and an illustration on the other of a wave releasing 230 seagulls. In July 2006, an abstract black granite statue of a 10-foot-high (3.0 m) lighthouse was added above a tomb holding many of the victims' personal belongings. The lighthouse statue was designed by Harry Edward Seaman, whose cousin died in the crash, and dedicated by George Pataki.[70]
Destruction of wreckage
For almost 25 years, the wreckage of Flight 800 was kept by the NTSB and used as an accident-investigation teaching aid. By 2021, the methods taught using the wreckage were determined to no longer be relevant to modern accident investigation, which by then relied heavily on new technology, including three-dimensional laser-scanning techniques.[71] The NTSB did not wish to renew the lease on the hangar it was using to store the reassembled accident debris, and decided it should be disposed of. Accordingly, the NTSB decommissioned the wreckage in July 2021.[72] As the NTSB had agreements with the victims' families that the wreckage cannot be used in any kind of public memorial or be scuttled in the ocean, it plans to scan each piece of debris with a three-dimensional laser scanner, with the data being permanently archived, after which the wreckage will be destroyed and the metal recycled. Any parts of the plane that cannot be recycled will be disposed of in landfills.[73][74] Destruction of the wreckage was scheduled for completion before the end of 2021.[72]
See also
Boeing 747 hull losses
Louis Freeh – director of the FBI from 1993 to 2001 who assisted in the crash investigation
Night Fall – 2004 New York Times best-seller by Nelson DeMille that revolves around a couple who witnessed and videotaped the crash of TWA Flight 800
Pan Am Flight 214 – an aircraft that suffered a fuel-tank explosion in midair in 1963, after being hit by lightning
Philippine Airlines Flight 143 – a similar incident in 1990 involving a 737, experienced a fuel-tank explosion on the ground, possibly caused by faulty wiring
Thai Airways International Flight 114 - a similar incident in 2001 involving a 737, experienced a fuel-tank explosion on the ground, possibly as a result of running the pump in the presence of metal shavings and a fuel/air mixture
South African Airways Flight 295 – another Boeing 747 crash giving rise to conspiracy theories
Courtney Whitmore – a DC Comics character based on the disaster's victim Courtney Elizabeth Johns; the younger sister of Geoff Johns
Notes
Captain Kevorkian had over 18,800 flight hours, including 5,490 hours on the Boeing 747. Flight 800 was actually a training flight for Kevorkian, and he was seated in the captain's (left) seat. Captain/Check Airman Snyder was seated in the first officer's (right) seat monitoring Kevorkian's progress. He had 17,000 flight hours, with more than 4,700 of them on the Boeing 747. Flight Engineer/Check Airman Campbell had 3,047 flight hours, including 2,397 of them on the Boeing 747 and was seated in the cockpit jump seat. Flight engineer trainee Krick was seated in the flight engineer's seat (being monitored by Flight Engineer/Check Airman Campbell); he was the least experienced of the crew, having logged 2,520 flight hours, but with only 30 of them on the Boeing 747.: 4–5
The NTSB Final Report gives Oliver Krick's age as being 24. The TWA press release gives 25.
No comments:
Post a Comment