TWA Flight 800

Reconstruction of TWA 800 wreckage
Summary
Date	July 17, 1996 [July 18 UTC]
Cause	Mid-air explosion
Site	Atlantic Ocean near East Moriches, New York
Origin	John F. Kennedy International Airport
Destination	Charles de Gaulle International Airport
Fatalities	230
Aircraft
Aircraft type	Boeing 747-131
Operator	Trans World Airlines (TWA)
Tail number	N93119
Passengers	212
Crew	18
Survivors	0

Trans World Airlines (TWA) Flight 800, a Boeing 747-131, N93119, crashed on July 17, 1996, about 20:31 EDT (00:31, July 18 UTC), in the Atlantic Ocean near East Moriches, New York. TWA Flight 800 was a scheduled international passenger flight from John F. Kennedy International Airport (JFK), New York, New York, to Charles de Gaulle International Airport (CDG), Paris, France. The flight departed JFK about 20:19, with two pilots, two flight engineers, 14 flight attendants, and 212 passengers on board. All 230 people on board were killed, and the airplane was destroyed.^[1]

While investigators from the National Transportation Safety Board (NTSB) arrived on scene the following day, much initial speculation centered on a terrorist attack,^[2][3] and consequently the Federal Bureau of Investigation (FBI) initiated a parallel investigation into the crash. On November 18, 1997, the FBI announced that no evidence had been found of a criminal act,^[4] and the NTSB assumed sole control on the investigation.

The NTSB investigation ended with the adoption of their final report on August 23, 2000. In it they concluded that the probable cause of the 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."<ref name="ntsb abstract" />

Many alternative theories exist as to the cause of this crash, most of which propose that evidence may exist that points to an external missile strike or on-board bomb, either as a terrorist act, or an unintentional shootdown by a U.S. Navy vessel.^[5][6][7] The NTSB investigation considered the possibility that a bomb or missile caused the mishap, but "none of the damage characteristics typically associated with a high-energy explosion of a bomb or missile warhead (such as severe pitting, cratering, petalling, or hot gas washing) were found on any portion of the recovered airplane structure".^[8]

Accident flight

On the day of the crash the airplane departed Athens, Greece, as TWA Flight 881, and arrived at the gate at JFK about 16:38. Upon arrival at JFK there was a crew change, and the aircraft was refueled.^[9] TWA Flight 800 was scheduled to depart JFK for CDG around 19:00, but the flight was delayed for just over an hour due to a disabled piece of ground equipment and a passenger/baggage mismatch.^[10] After it was confirmed the owner of the baggage in question was on board, the flight crew prepared for departure, and the aircraft pushed back from the gate about 20:02.<ref name="ntsb final" />

Data recovered from the Cockpit Voice Recorder (CVR) and Flight Data Recorder (FDR) indicated a normal departure from JFK about 20:19.^[11][12] TWA 800 then received a series of generally increasing altitude assignments and heading changes as it climbed to its intended cruising altitude.^[13] The last radio transmission from the airplane occurred at 20:30 after the flight crew received and then acknowledged instructions from Boston Air Route Traffic Control Center (ARTCC) to climb to 15,000 feet.<ref name="ntsb atc" /> TWA 800 was in the process of climbing when the CVR and FDR both abruptly stopped recording data at 20:31:12.<ref name="ntsb fdr" /><ref name="ntsb cvr" /> This was the same time as the last recorded radar transponder return from the airplane was recorded by the Federal Aviation Administration (FAA) radar site at Trevose, Pennsylvania.<ref name="ntsb final" />

At 20:31:50 the captain of an Eastwind Airlines Boeing 737 first reported to Boston ARTCC that he "saw an explosion out here", adding "ahead of us here...about 16,000 feet or something like that, it just went down into the water."<ref name="ntsb atc" /> Subsequently, many Air Traffic Control (ATC) facilities in the New York/Long Island area received reports of an explosion from other pilots operating in the area.<ref name="ntsb atc" /> Other witnesses on land and sea later stated that they saw and/or heard explosions, accompanied by a large fireball over the ocean, and observed debris, some of which was burning, falling into the water.<ref name="ntsb final" /> About one-third of these witnesses reported that they observed a streak of light moving upward in the sky to the point where a large fireball appeared.<ref name="ntsb final" />

Although individuals in various civilian, military, and police vessels reached the crash site and initiated a search within minutes of the initial water impact, no survivors were found.<ref name="ntsb final" />

Family members of Flight 800 victims, investigators, media members, and TWA employees gathered at the Ramada Inn at JFK Airport, causing the hotel to be called "Crash Central" [1].

Initial investigation

Fundamental principles of accident investigation

Accident investigation is a process of elimination. There are many possibilities at the start of an investigation. The FBI will be involved as necessary until criminal act is eliminated as a probable cause. Teams are assembled to investigate various aspects of an accident and include "interested parties." Those interested parties include the aircraft manufacturer, the Airline Pilots Association, the manufacturers of the engines and various subsystems, the Airlines and Federal Aviation Agency. The goal is to eliminate possible causes until a "most probable cause" is arrived at.

Wreckage recovery

Search and recovery operations were conducted by federal, state, and local agencies, as well as their contractors.^[14] The first priority of the early search and recovery efforts was the recovery of the victims; wreckage recovery was the second priority.<ref name="ntsb final" /> Remote-operated vehicles (ROV), side-scan sonar, and laser line-scanning equipment were used to search for and investigate underwater debris fields.<ref name="ntsb appendixes" /> Victims and wreckage were recovered by Scuba divers and ROVs; later scallop trawlers were used to recover wreckage embedded in the ocean floor.<ref name="ntsb appendixes" /> Numerous recovery divers required hyperbaric oxygen treatments for decompression sickness.^[15] As the wreckage recovery progressed, three main debris fields emerged. The yellow zone, red zone, and green zone contained wreckage from front, center and rear sections of the airplane, respectively.<ref name="ntsb final" /> The red zone was the most widespread and contained primarily fuselage structure from stations 840 to 1000. It also contained most of the wing center section Front Spar, Span Wise Beam 3 and the forward portion of the keel beam and cabin floor from above the forward center section. Some pieces of wreckage from the red zone had light soot deposits, none contained either moderate or heavy soot deposits. There was no evidence of other exposure to fire on wreckage recovered from the red zone.^[16] The yellow zone contained the nose of the airplane forward of station 840, including the cockpit. This structure hit the water basically intact and showed extensive crushing damage. Wreckage recovered from the yellow zone showed no evidence of soot, fire or heat.^[17] The green zone with the aft portion of the fuselage, wings and engines, was located the furthest along the flight path. Wreckage from the green zone showed varying amounts of soot, fire and heat damage, much of it extensive, depending upon location and when they separated from the rest of the structure.^[18] The pattern of fire damage upon the wreckage shows that the wreckage resulting from the initial breakup (red zone) had only slight indications of combustion, the nose section which fell further along the flight path had none, and all major evidence of fire occurred upon the wreckage of the aft fuselage and wings which were furthest down the flight course. This shows that aside from the initial explosion inside the Center Wing Tank all fire happened after the aircraft broke up.^[19]

Remains of all 230 victims and over 95% of the airplane wreckage were eventually recovered.<ref name="ntsb appendixes" />^[20] A temporary morgue facility at the United States Coast Guard station at East Moriches initially documented the human remains which were then transported to a permanent morgue facility at the Suffolk County Medical Examiner's Office in Hauppauge, New York.<ref name="ntsb forensic" /> Pieces of wreckage were transported by boat to shore and then by trucks to leased hangar space at the former Grumman Aircraft facility in Calverton, New York for storage, examination and reconstruction (this facility became the command center and headquarters for the investigation).<ref name="ntsb appendixes" /> NTSB and FBI personnel were present to observe all wreckage transfers to preserve the evidentiary value of the wreckage.<ref name="ntsb appendixes" /> Initial examination of the wreckage revealed potential explosive residue on three samples of material from separate locations in the airplane wreckage; further testing determined that one contained traces of cyclotrimethylenetrinitramine (RDX), another nitroglycerin, and the third a combination of RDX and pentaerythritol tetranitrate (PETN).<ref name="ntsb final" /> None of the sample locations correlated to the source of the explosion in the center wing tank. There was none of the readily apparent damage caused by a high-explosive detonation in an aircraft found on any of the structure or contents.^[21]

The wreckage is now permanently stored in a facility in a NTSB facility in Ashburn, Virginia which was custom built for the purpose. The reconstructed aircraft is used to train accident investigators.^[22][2]

Cockpit Voice Recorder and Flight Data Recorder evidence

There was nothing unusual on the Cockpit Voice Recorder (CVR) tape until 2029:15 when the Captain stated: “"Look at that crazy fuel flow indicator there on number four. . . see that?"^[23] Boston Air Route Traffic Control Center cleared TWA 800 to climb to and maintain 15,000 feet at 2030:15, followed by the Captain ordering "climb thrust" and acknowledging the ATC clearance in the next few seconds. At 2030:35 the Flight Engineer said "power's set."^[23] At 2030:42 the Cockpit Area Microphone recorded a mechanical movement in the cockpit, followed by an unintelligible word at 2031:03, followed by sound similar to "recording tape damage" at 2031:05. The tape suddenly ended at 2031:12. Sound spectrum analysis revealed that during the last second of recording there were two unusual events on the Captain's microphone channel where a brief 400 Hertz sound was recorded. (The aircraft's AC power system normally operates at 400 Hz line frequency.)^[24] Other background electrical noise normally recorded on that channel ceased during the two transient events, .73 and .68 seconds before the end of the tape. The other CVR channels recorded normally.^[25] The last event on the CVR tape occurred on all channels, and involved a very short, loud noise lasting .117 seconds before the tape ended. The CVR tape ended with power failure at 2031:12, which was the same time as the last radar transponder return was received from the aircraft.^[25]

The loud transient noise at the end of Flight 800s Cockpit Voice Recorder tape was compared to the similar noises on the recorders of two 747s that were destroyed by bombs in the forward cargo compartment, Pan Am 103 and Air India 182. It was also compared to the event on the tape of United 811, a 747-100 which suffered an explosive decompression due to failure of the forward cargo compartment, and with the explosion recorded on the CVR tape of a Philippine Airlines 737 which had suffered a fuel/air mixture explosion in its center wing tank on the ground. The bombed aircraft tapes showed a very rapid rise in noise level, brief duration, and a very rapid decline in the noise of the explosion. In the case of the other three aircraft, including TWA 800, the rate of the rise of the noise was more gradual, the duration of peak noise longer, and the decline of the noise was more gradual.^[26]

The flight data recorder data was consistent with an aircraft in a normal, wings level climb when the recorder suddenly stopped due to termination of electrical power.^[27]

Witnesses

Interviews with potential witnesses to the TWA 800 crash were conducted by the FBI; the NTSB was asked not to interview or re-interview witnesses because multiple interviews could lead to difficulties in any potential future criminal prosecution.^[28] No verbatim records of the witness interviews were produced; instead the agents who conducted the interviews wrote summaries of the interviews which they then submitted.<ref name="ntsb witnesses" /> Witnesses were not asked to review or correct the documents.<ref name="ntsb witnesses" /> After the FBI closed their active criminal investigation, the summaries were handed over to the NTSB (with personal information of the witnesses redacted), who then formed a witness group to review these documents.<ref name="ntsb witnesses" />

The NTSB witness group reviewed the summaries and determined they contained 736 witness accounts.^[29] Of these, the group determined that 670 witnesses reported seeing something that probably related to the accident, and almost 250 reported hearing something that was likely related to the accident.<ref name="ntsb witness study" /> 239 reported hearing something variously described as an "explosion, boom, rumble, [or] thunder" mostly along the South Shore of Long Island, at 15 to 20 km slant range distance.^[30] 258 accounts 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.")<ref name="ntsb witness study" /> Of these 258 witnesses, 38 reported that the streak was ascending vertically or nearly so, 18 indicated that it originated from the surface of the earth, and 7 reported that it originated at the horizon.<ref name="ntsb witness study" />

599 witnesses reported a fireball; of these 264 reported seeing the fireball originate, 200 reported seeing the fireball split into two, and 217 reported observing the fireball hit the surface of the water, or disappear below the horizon.<ref name="ntsb witness study" /> 210 witnesses reported seeing both a fireball and a streak of light.<ref name="ntsb witness study" />

Further investigation and analysis

Accident sequence

Careful analysis of the distribution of the wreckage, the damage found, and patterns of soot and burning, all contributed to understanding the sequence of events during the breakup of the aircraft. Fire was not present at the beginning of the event, and was produced as the result of the systematic failure of the aircraft structure and tanks containing fuel.^[31]

The destruction sequence started with a low-order explosion originating within the center fuel tank. The explosion inside the center fuel tank caused the spanwise beam, which was the front of the tank, to fail, rotating it downward and forward, where it struck the front spar (one of two major structural components carrying lift loads across the span of the wing); it caused bowing and fractures of the front spar. At this time the over-pressure escaping the center wing tank caused the upper wing skin to separate from the front spar, followed by the lower wing skin and keel beam being forced downward. The fractures were continued to the lower pressure bulkhead and caused cracking of the fuselage skin starting immediately forward of the wing spar. This led to the destruction of the lower fuselage comprising the forward cargo compartment. That was followed by the propagation of cracking upward around the fuselage sides forward of the wing center section. The pattern of cracks spreading upward caused a compression failure of the window belt above the hole in the lower fuselage, followed by complete failure of the fuselage structure above the leading edge of the center section, and separation of the entire nose.^[31]

At this point the aircraft pitched up due to the aft shift in the center of gravity, which induced a climb and imposed aerodynamic loads which soon caused failure of the wing center section by bending loads. The bending loads caused the left wing to come off. It was during this sequence that evidence of fire started to appear on the aircraft due to the burning of fuel leaking from ruptured tanks (92% of all victims with burns were seated over the Center Section Fuel Tank, which remained attached to the aft fuselage).^[32] Most fire damage on the left wing was outboard of the number 1 engine. There was severe fire damage to the left end of the number 2 Span Wise Beam as well as extensive burning of the cabin area over the Center Wing Tank, which may account for the streak seen rising by some witnesses. Soot stains indicated that the right wing came off the fuselage after the left, and in stages, leaving a stub attached to the aft fuselage. This area and the area behind it along the fuselage showed the most extensive fire damage. The progressive fragmentation and burning of the right wing would have produced a 'fireball' when viewed from a distance. The majority of the after fuselage struck the water as a single large piece further down the flight path than the nose and much further than the fuselage fragments created by the disintegration of the fuselage structure just forward of and above the center fuel tank.^[33]

The wreckage from the area immediately forward of the wing, and parts of the center section were distributed widely almost below where radar indicated the breakup started. The nose section was within the outermost area of the that wreckage and further along the flight heading. The wings and aft fuselage, which pitched up when the nose came off, continued in crippled flight briefly, then fell farther along the flight path.^[33]

The distribution of the parts of the wings and fuselage down the flight path, and the soot damage from the in-flight fires coincided, proving the order in which the structure disintegrated.^[31]

Possible reasons for the in-flight breakup

Witness reports and the distribution of wreckage indicated a catastrophic in-flight breakup of TWA 800.<ref name="ntsb final" /> The NTSB considered as possible causes "structural failure and decompression; detonation of a high-energy explosive device, such as a bomb exploding inside the airplane or a missile warhead exploding upon impact with the airplane; and a fuel/air explosion in the center wing tank (CWT)."<ref name="ntsb final" />

Structural failure and decompression. Close examination of the wreckage revealed no evidence of structural faults such as fatigue, corrosion or mechanical damage that could have contributed to the in-flight breakup.<ref name="ntsb final" /> It was also suggested that the breakup could have been started with an in-flight separation of the forward cargo door; however all evidence indicated that the door was closed and locked at impact.<ref name="ntsb final" /> The NTSB determined that "the in-flight breakup of TWA flight 800 was not initiated by a preexisting condition resulting in structural failure and decompression."<ref name="ntsb final" />



High-energy explosive device detonation. Factors such as heightened security and safety concerns because of the 1996 Olympics, that TWA 800 was an international flight, witness reports of a streak of light and then a fireball, as well unexplained targets near TWA 800 recorded by a radar site at Islip, New York, led the NTSB to consider the possibility that a bomb exploded inside the airplane or that a shoulder-launched missile exploded upon impact with the airplane.<ref name="ntsb final" />

The backs of several damaged passenger seats were observed to have an unknown red/brown-shaded substance on them; subsequent investigation along with testing by NASA determined this substance to be consistent with adhesive used in the seats.<ref name="ntsb final" /> Earlier, the FBI had detected trace amounts of explosive residue on three separate pieces of the wreckage (described as a piece of canvas-like material and two pieces of a floor panel).<ref name="ntsb final" /> However, no damage typically associated with a high-energy explosion of a bomb or missile warhead ("severe pitting, cratering, petalling, or hot gas washing") were found on the recovered wreckage, including the pieces which tested positive for explosives.<ref name="ntsb final" /> Of the 5 percent of the fuselage that was not recovered, none of the missing areas were large enough to have covered all the damage that would have been caused by the detonation of a bomb or missile.<ref name="ntsb final" /> In addition, none of the victims' remains showed evidence of injuries that could have been caused by high-energy explosives.<ref name="ntsb final" />

The NTSB considered possible reasons why the wreckage would test positive for explosive residue, including the aircraft's use in 1991 transporting troops during the Gulf War, as well as its use in a dog-training explosive detection exercise about one month before the crash.<ref name="ntsb final" /> However, testing by the FAA's Technical Center concluded that residues of the type of explosives found on the wreckage would completely dissipate after just 2 days of immersion in salt water, and would not be detectable.<ref name="ntsb final" /> The NTSB concluded that it was "quite possible" that the explosive residue detected was deposited during or after wreckage recovery operations.<ref name="ntsb final" /> When the radar data from the Islip facility was analyzed, none of the unexplained radar returns intersected TWA 800's flight path at any time, and all of them were moving away from the airplane.<ref name="ntsb final" /> The lack of any corroborating evidence associated with a high-energy explosion led the NTSB to conclude that "the in-flight breakup of TWA flight 800 was not initiated by a bomb or missile strike."<ref name="ntsb final" />



Fuel/air explosion in the center wing fuel tank. The NTSB established a sequencing group to determine the sequence of the airplane's structural breakup and compare proposed accident scenarios with the structural observations.<ref name="ntsb final" /> The group concluded that the first event in the breakup sequence was a failure in the structure of the CWT, caused by excessive pressure ("overpressure") within the CWT.<ref name="ntsb final" /> This led to a series of structural failures, culminating in the complete separation of the forward fuselage and destruction of the airplane.<ref name="ntsb final" />



The investigation then focused on the fuel/air vapors present in the CWT (only a residual amount of fuel was present in the CWT for the flight), and whether they were flammable and the cause of the overpressure event. Examination of the heat flow around the CWT revealed that the airplane's air conditioning packs, located underneath the CWT, may have contributed to heating of the fuel/air vapor while operating for 2 1/2 hours at the gate at JFK.<ref name="ntsb final" /> Tests recreating the conditions of the flight showed temperatures of the fuel/air vapor in the CWT ranging from 101 to 127 °F (38 to 53 °C)<ref name="ntsb final" /> while Jet A fuel/air vapors under the same conditions as the flight were flammable at temperatures as low as 96.4 °F (35.8 °C).<ref name="ntsb final" /> Questions were raised whether a fuel/air vapor explosion in the CWT would generate enough force to break apart the CWT and cause the destruction of the airplane.<ref name="ntsb final" /> Computer modeling and quarter-scale experiments using models of the CWT were used to investigate the mechanics of a CWT explosion.<ref name="ntsb final" /> During these experiments "quenching" of explosions within the CWT was observed, where the internal structure of the multi-compartment fuel tank did not allow for explosions to develop with enough force to cause the expected damage.<ref name="ntsb final" />

Further computer modeling was conducted, and in July and August 1997, using an out-of-service 747 at Bruntingthorpe Airfield, England, tests simulated a fuel/air explosion in the CWT by igniting a propane/air mixture. These tests resulted in the failure of the CWT structure due to overpressure.<ref name="ntsb final" /> The NTSB acknowledged that these test conditions were not fully comparable to the conditions that existed on TWA 800 at the time of the accident, but previous accidents involving CWT explosions of Jet A fuel, notably Avianca Flight 203 and Philippine Airlines Flight 143 led the NTSB to conclude "On the basis of the accident airplane's breakup sequence; wreckage damage characteristics; scientific tests and research on fuels, fuel tank explosions, and the conditions in the CWT at the time of the accident; and analysis of witness information, the Safety Board concludes that the TWA flight 800 in-flight breakup was initiated by a fuel/air explosion in the CWT."<ref name="ntsb final" />

Possible ignition sources of the center wing fuel tank

In an attempt to determine what ignited the flammable fuel/air vapor in the CWT and caused the explosion, the investigation evaluated numerous potential ignition sources. All but one were considered "very unlikely", while one was considered "likely"<ref name="ntsb final" />

Missile fragment. Although the NTSB had already reached the conclusion that a missile-strike was not the cause of the structural failure of the airplane, they considered 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 characteristics of a missile strike.<ref name="ntsb final" /> Using data provided by the Naval Air Warfare Center, Survivability/Vulnerability Information Analysis Center, and Missile and Space Intelligence Center, computer simulations were constructed to simulate a missile detonating in a location such that a fragment from the warhead could penetrate into the CWT.<ref name="ntsb final" /> Based on these simulations the investigation concluded that it was "very unlikely" that a warhead detonated in such a location where a fragment would penetrate the CWT, but no other fragments impact the surrounding airplane structure.<ref name="ntsb final" />

Small explosive charge. Similarly, the investigation considered the possibility that a small explosive charge placed on the CWT could have been the ignition source.<ref name="ntsb final" /> Testing by the NTSB and the British Defence Evaluation and Research Agency demonstrated that when the metal of the same type and thickness of the CWT was penetrated by a small charge, there was petalling of the surface where the charge was placed, pitting on the adjacent surfaces, and visible hot gas washing damage in the surrounding area.<ref name="ntsb final" /> Since none of the recovered CWT wreckage exhibited these damage characteristics, and none of the areas of missing wreckage were large enough to encompass all the expected damage, the investigation concluded that this scenario was "very unlikely"<ref name="ntsb final" />

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.<ref name="ntsb final" /> After analysis the investigation determined that these potential sources were "very unlikely" to have been the source of ignition.<ref name="ntsb final" />

Fuel quantity indication system. The FAA and airplane manufacturers had assumed that a flammable fuel/air mixture would exist at all times in fuel tanks; consequently airplane designers attempted to eliminate all possible sources of ignition in the fuel tanks The primary means of ensuring this is to keep voltages and currents being used by the fuel quantity indication system very small, and to protect all devices from intrusion of vapor.<ref name="ntsb final" /> In the case of the 747-100 series, the only wiring located inside the CWT was wiring associated with the Fuel Quantity Indication System (FQIS).

As part of the NTSB's investigation, Boeing submitted a fault tree analysis of possible ignition mechanisms in the CWT (such an analysis was not performed nor required in December 1969 when the 747-100 series was certified by the FAA).<ref name="ntsb final" /> This analysis concluded that the probability of an FQIS wiring fault producing an ignition source in the CWT as being 1 x 10^-6 events per hour.<ref name="ntsb final" /> Regulatory guidelines that were later adopted in April 1970 by the FAA required probabilities of such failures to be less than 1 x 10^-9 (this was considered to be "extremely improbable" and "not anticipated to occur during the entire operational lifetime of all airplanes of one type.")<ref name="ntsb final" /> However a review of Boeing's fault tree analysis by NASA's Marshall Space Flight Center (MSFC) strongly criticized the accuracy of its findings, concluding that the fault tree analysis quantifications "cannot stand up to peer review and should not be viewed as realistic."<ref name="ntsb final" /> Further study by MSFC personnel indicated that "realistic" numbers used in a fault tree analysis would indicate a much higher probability of ignition through the FQIS wiring system.<ref name="ntsb final" />

The FQIS was designed to use voltage so low as to prevent it from being a possible ignition source.<ref name="ntsb final" /> Therefore, in order for the FQIS to be the ignition source, a transfer of higher than normal voltage to the FQIS needed to have occurred, as well as some mechanism whereby the excess energy got released by the FQIS wiring into the CWT.<ref name="ntsb final" /> While the NTSB determined that factors suggesting the likelihood of a short circuit event existed,<ref name="ntsb final" /> they added that "neither the release mechanism nor the location of the ignition inside the CWT could be determined from the available evidence."<ref name="ntsb final" /> Nonetheless, the NTSB concluded that "the ignition energy for the CWT explosion most likely entered the CWT through the FQIS wiring."<ref name="ntsb final" />

Though the FQIS itself was designed to prevent danger from its normal operation, this requires the use of very low voltages and currents. The innermost tube of the FQIS compensator showed damage similar to that of the compensator tube which was the ignition source for the surge tank fire which destroyed a 747 near Madrid in 1976.^[34] This was not considered 'proof' of a source of ignition. There was evidence of arcing in a wire bundle which included FQIS wiring which connected with the Center Wing Tank.^[35] There was also arcing evidenced on two wires sharing a cable raceway with FQIS wiring at station 955.^[35]

The Captain's Cockpit Voice Recorder channel showed two 'dropouts' of background power harmonics in the second before the recording ended (with the separation of the nose).^[36] 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 gage about 2-1/2 minutes before the CVR recording ended.^[37] Finally, the Center Wing Tank fuel quantity gage was recovered and indicated 640 pounds instead of the 300 pounds which was loaded into that tank.^[37] 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.^[37] 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, it is not possible to pin-point the source of the necessary voltage.

Analysis of reported witness observations

Numerous witnesses in the vicinity of the accident reported a streak of light. As the NTSB noted, "There was intense public interest in these witness reports and much speculation that the reported streak of light was a missile that eventually struck TWA flight 800, causing the airplane to explode."<ref name="ntsb final" /> The NTSB Witness Group concluded that the streak of light reported by witnesses might have been the accident 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 flightpath of the accident airplane after the CWT explosion.<ref name="ntsb final" />

However, 38 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 flightpath."<ref name="ntsb final" /> In addition, 18 witnesses reported seeing a streak of light that originated at the surface, or the horizon, which was "not consistent with the airplane's flightpath."<ref name="ntsb final" /> With regard to these differing accounts, the NTSB noted that in previous investigations witness data was "often inconsistent with the known facts or other witnesses' reports of the same events."<ref name="ntsb final" /> The interviews conducted by the FBI focused on the possibility of a missile attack (some suggested interview questions given to FBI agents were "Where was the sun in relation to the missile launch point?" and "How long did the missile fly?"), and as a consequence there was possible interviewer/interviewee bias.<ref name="ntsb witness study" /> 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"<ref name="ntsb final" />, and "did not view the apparent anomalous accounts as being persuasive evidence that some witnesses might have observed a missile."<ref name="ntsb final" />

The investigation determined that if witnesses had observed a missile attack they would have seen the following: (1) a light from the burning missile motor ascending very rapidly and steeply for about 8 seconds; (2) the light disappearing for up to 7 seconds; (3) upon the missile striking the aircraft and igniting the CWT another light, moving considerably slower and more laterally than the first, for about 30 seconds; (4) this light descending while simultaneously developing into a fireball falling toward the ocean.<ref name="ntsb final" /> None of the witness documents provided to the NTSB described such a scenario, and the investigation concluded that "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 the burning fuel from the accident airplane in crippled flight during some portion of the post-explosion, pre-impact breakup sequence."<ref name="ntsb final" />

Conclusions

In addition to the probable cause, the NTSB found the following contributing factors to the accident:<ref name="ntsb final" />

• 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 nonflammable.

During the course of their investigation, and in their final report, the NTSB issued 15 safety recommendations, mostly covering fuel tank and wiring-related issues.<ref name="ntsb final" /> 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, to existing airplanes (such an inerting system prevents fuel tank explosions by pumping nitrogen into fuel tanks to displace oxygen).<ref name="ntsb final" />

See Also

• Pan Am Flight 214 - December 8, 1963

Alternative theories

Further information: TWA Flight 800 alternative theories

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."^[38] It is, however, normal for the NTSB to make such a statement when asked about an ongoing investigation. Speculation was fueled in part by early descriptions, visuals, and eyewitness accounts of this jet disaster, including a sudden explosion and trails of fire in the sky; particularly, trails of fire moving in an upward direction.

The two most prevalent specific theories around TWA 800 are that of a terrorist bomb on board, or a missile striking the plane (attributed to American armed forces by some and to terrorists by others). Those supporting these alternative explanations for the crash typically claim that the NTSB's explanation, above, was created as a cover-up; that the NTSB did not investigate sufficiently; or that the NTSB did not have all the evidence they should have had to reach the correct conclusion.

An electrical short in the center main fuel tank's scavenge pump, or the wiring to the scavenge pump. This scavenge pump removes the last 50 gals of ullage Jet-A from the CMT to the number two (left main wing) tank. This transfer of fuel is normally done between 10,000' and 15,000' with the center main tank empty on takeoff, or when the center main fuel tank is run dry with the four center main fuel tank override/jettison pumps. (2 FWD, 2 AFT)

The scavenge pump from TWA Flight 800 has not been recovered.

Notable victims

Some of the notable passengers on TWA 800 included:^[39]

• David Hogan, American composer.
• Marcel Dadi, French guitarist.
• Rico Puhlmann, German fashion photographer.
• Sylvain Delange, French artist.
• Mohammed Samir Ferrat, Algerian businessman.
• Dan Gabor, University of Arkansas All-American track athlete.
• Jed Johnson, interior designer and director of the 1977 movie Andy Warhol's Bad.
• Michel Breistroff, French hockey player.
• Pam Lychner, a Spring Valley, Texas (near Houston) http://www.houstonpress.com/1997-10-23/news/after-the-crash/ real estate agent that promoted the "Pam Lychner Sexual Offender Tracking and Identification Act of 1996" bill after being assaulted in a vacant house. After Lychner and her daughters died on Flight 800, the United States Congress passed the bill http://www.ojp.usdoj.gov/BJA/what/2a2jwactbackground.html. The City of Spring Valley posted a statue of Lychner and her daughters at the city hall http://www.houstonpress.com/1997-10-23/news/after-the-crash/5.
• Ana Maria Shorter, wife of Composer and saxophonist Wayne Shorter.

In addition, 16 members of the French club at Montoursville High School in Montoursville, Pennsylvania, and their five chaperones were on-board.^[40]

TWA 800 in the media

• The incident was used as the basis for the 2000 horror movie Final Destination.
• CNN produced a two-hour documentary on the crash titled No Survivors: Why TWA 800 Could Happen Again.
• Nelson DeMille wrote a fictional novel, Night Fall, regarding the events surrounding TWA 800. In the novel, a couple conducting an illicit affair on the beach inadvertently capture the disaster on video.^[41]
• The crash was the subject of an episode of the documentary series Seconds From Disaster.
• The incident was used as the inspiration for "Dee's Heaven," one of the stories in the first issue of a comic book entitled Serina, Blade of the Pharaoh.^[42]
• The DC Comics character Stargirl, previously the second Star-Spangled Kid, was created by Geoff Johns, who is said to have based her personality on that of his sister Courtney Johns, who died in the explosion.^[43]
• Flight 800 was the subject of the premiere episode of Best Evidence, a documentary show on Discovery Channel.
• The same aircraft (N93119) that became TWA 800 can be seen taking off mid-way through the film Nine to Five.

References

External links

• Learning from a Tragedy: Explosions and Flight 800
• NTSB TWA 800 Board Meeting
• Photos of N93119 at Airliners.net
• Aviation Safety Network - TWA 800

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