NTSB Board Meeting on TWA 800
August 22, 2000
Day 1 of 2
Morning Session
Jim Hall: Good morning and welcome to this meeting of the National Transportation Safety Board. This morning's agenda item is an aviation accident report, carried as Board notation 6788G, an in-flight break-up over the Atlantic Ocean of Trans World Airlines Boeing 747-131, Registration N93119 that occurred near East Moriches, New York on July 17, 1996.
Under the Government in Sunshine Act, multi-member federal agencies, such as the Safety Board, conduct much of their business in open session. Therefore Board meetings are often called "Sunshine meetings." While the public is invited to observe today's meeting, only the Board Members and NTSB staff will participate in discussions. Today's meeting is also being simulcast to a worldwide audience on our website at http://www.ntsb.gov/.
A handout is available to our guests at the entrance to the Boardroom reiterating the information about the investigative process. Copies of a pamphlet that explains the Board and its work in some detail are also available there, and general information is also available on the Board's website.
During this meeting, the Board Members will discuss a draft report that has been prepared by staff. Because it is at this point just a draft, it is not available to the public. We will discuss the report section by section, soliciting staff comments and explanations on many points. Once we have reviewed all the issues, we will consider the staff's draft conclusions, probable cause determination, and specific safety recommendations. We will then determine if we should approve the draft with any revisions that we have discussed.
Sometimes all or part of a draft conclusion, probable cause, or recommendation is revised or rejected by the Board Members. That is because you are reviewing the Board's actual deliberations over this document. That is the purpose of the Sunshine Act - to provide the public with a window into the decision-making process.
Now, a couple of brief administrative announcements for those in our audience. In the event of an emergency, such as a fire, the building alarm system will activate and a voice message will instruct that we vacate the building. You should proceed to the nearest exit. There are emergency exits up here to the left and right of the platform and at the back of the room.
Restrooms are located in the foyer on the left as you exit this room, and on the promenade level above us. You may use the phones in the foyer for local and credit card calls. Cell phones will work if you walk outside this room. Most do not work in here, nor do most pagers. There are many eating establishments on the promenade level. Please understand that food and drink of any kind may not be brought into the meeting room.
There are many members of the NTSB staff here today. I know they will be glad to assist you in any way they can. Please do not hesitate to ask them for help if any of us can provide assistance.
Ladies and gentlemen, almost 1,500 days have passed since that terrible day in July 1996 when TWA Flight 800 crashed off the coast of Long Island, New York. It was a tragic event that stirred strong emotions and feelings throughout this country and throughout the world.
We had an airline of world renown, a category of aircraft, the Boeing 747, that had compiled an outstanding safety record in some three decades of service - and yet, 230 individuals lost their lives in a very few stark moments.
The crash of Flight 800 graphically demonstrates that even in one of the safest transportation systems in the world, things can go horribly wrong. It should stand as a reminder to all of us of the need for diligence and aggressive action in identifying and eliminating potential safety problems.
I would like to welcome at this time and acknowledge the presence here today of many of the 800 family members. These next two days, as the last four years have been, may be difficult for you. But I do hope that you take some comfort from seeing the great amount of work that has gone into this investigation. I want you to know that all our efforts have been aimed at preventing similar tragedies in the future.
I would also again express my appreciation to the authorities in New York - to the police, the divers, the fire rescue and emergency assistance units, the Red Cross, the Salvation Army, as well as the many private citizens - who made valiant efforts in the immediate hours and days after the aircraft went down. I would also like to thank the Coast Guard, the Navy, the FBI, NOAA [National Oceanographic and Atmospheric Administration], and the many other state and federal agencies that assumed major roles in the search and recovery effort.
I would like to note the encouragement and support we have received from the White House and Congress in providing the resources needed to conduct what has become the most extensive, complex, and expensive investigation in the Safety Board's 33-year history.
From the beginning, the scope and dimensions of this investigation have been extraordinary. The salvage effort organized by the Navy, one of the largest diver-assisted salvage operations ever conducted, extended from July to November 1996. The Navy divers worked in very difficult and dangerous conditions, and for a time their efforts had to be halted because of the onset of the Atlantic hurricane season. When the diving operations were completed, there followed months of work by contracted fishing trawlers that scoured hundreds of miles of the ocean floor. In the end, we recovered the remains of all 230 victims and more than 95 percent of the aircraft.
The reconstruction of a 93-foot segment of the aircraft fuselage, including the center wing fuel tank, was unique both in size and scope. More than 30 people worked meticulously for many months to sort through innumerable pieces of wreckage and assemble the reconstruction in an effort to better understand what happened to Flight 800.
The number of organizations, public and private, that played a significant role in this investigation is extensive. I'd like to pause for a few minutes, so you can see the almost 500 names of those entities and individuals that contributed to the investigative process. I direct your attention to the screens in front of you. The Safety Board staff and various government and private research organizations, under contract to the National Transportation Safety Board, undertook an unprecedented amount of research and testing that was paid for by the American taxpayers.
For example, Safety Board staff leased a Boeing 747 to study the temperatures and environment inside the aircraft's center wing tank. We also conducted extensive research into the composition and explosive characteristics of Jet A fuel. In addition, we conducted test and computer simulation work to study flame and pressure propagation in the center wing tank. Early on in the process, investigators began looking at what role electromagnetic interference from external emitters or sources internal to the aircraft may have played in the crash.
The investigation also included the most extensive radar data study in the Board's history, including a review of several hundred thousand radar returns from nine radar locations in five states. The investigative team also spent a great deal of time organizing and carefully analyzing the summaries of witness interviews the Federal Bureau of Investigation provided to the Board. We will be reviewing the work done by the witness group, and many of the others, during the course of this meeting.
All of the investigative work undertaken as part of this investigation was extremely complex. Because of the need for precision and, in some cases, the danger posed to those performing the tests, the work had to be painstakingly done to make sure that it was done properly, safely, and accurately. And, of course, it was not inexpensive.
We were fortunate to secure the assistance of a broad array of institutions, including the Department of Defense laboratories at Wright-Patterson Air Force Base and the Navy's China Lake and Patuxent River facilities. Important work was also done at NASA's Langley Research Center and the Sandia Laboratories, among others.
We also contracted with private institutions, such as the California Institute of Technology and the University of Nevada, Reno, and various specialties to conduct research. Experts from other countries, including the United Kingdom, Norway, and Canada, also assisted us, and the French aviation authorities participated under the terms of the Convention on International Civil Aviation.
Much has been learned over the course of the past four years, and the five Board Members seated before you will be examining and discussing the results of the staff's work during this Sunshine meeting. I must emphasize that over the next two days you will observe some extremely technical discussions about the issues raised in the investigation. In preparation for this meeting, the Board Members each read the 684-page report and the 177 pages of information that were provided in party submissions. The extensive record of this investigation now approaches some 15,000 pages and is available to everyone in the Board's public docket. The investigative groups' factual reports can also be found on our web page. The other supporting documentation is available in CD-ROM format.
During the course of this investigation, the Board received a great number of suggestions and comments from many individuals and organizations on possible causes of the crash of Flight 800 and recommendations for possible lines of investigation. Much of this commentary has been well informed, and we appreciate receiving it. Safety Board staff has reviewed all of this material, and took those ideas that appeared to have a scientific basis and offered a reasonable line of inquiry into account as the accident investigation progressed.
In the early months of the investigation, it became clear that an explosion of flammable vapors in the aircraft's center wing tank initiated the break-up and subsequent crash of Flight 800. In December 1996, based on the Board's conclusion that heated, flammable vapors in the aircraft fuel tank pose a serious risk to safe flight, the Board recommended that the Federal Aviation Administration study design changes to deal with this problem and that, in the interim, they require operational changes to enhance safety. In April 1998, the Board issued another set of recommendations focused on aircraft wiring and the fuel quantity indication system. During this meeting, we will be assessing what has been done in response to those recommendations, as well as what as what remains to be accomplished.
More broadly, the Flight 800 investigation has uncovered and focused the attention of the aviation community on some very important safety issues - fuel tank protection, the vulnerability of aircraft wiring, and a number of aging aircraft issues. We will pursue each of these items in some detail over the next two days. This is a lot of ground to cover, but before moving ahead, I would like to make one additional comment.
I know that at the outset many believed that the crash of Flight 800 was caused by a criminal act. And for many the events of the times - the ongoing court trials in the aftermath of the World Trade Center bombings in New York, and the heightened concern about terrorism at the 1996 Olympic Games in Atlanta - seemed to lend a certain credence to the notion. Certainly, the nature of the event and its rarity led some to question whether the crash of Flight 800 was really an accident.
As many of you know, a substantial law enforcement investigation was conducted in parallel with the Safety Board's investigation. After conducting a thorough investigation, the FBI suspended its investigation in November 1997, indicating that no evidence had been found to indicate that a criminal act was the cause of the tragedy of TWA Flight 800.
Despite this finding by our nation's law enforcement agency, the Federal Bureau of Investigation, some have urged the Safety Board to assume, in effect, a law enforcement role to prove or disprove their assertion that the crash of Flight 800 was the result of a bomb or a missile. That is beyond this agency's mandate and authority. Our focus is safety. Our people are aviators, engineers, and scientists - I believe, some of the best in the world - but they are not criminal investigators.
However, even though our employees are not law enforcement personnel, they examined every piece of wreckage for any physical evidence that the crash of Flight 800 had been caused by a bomb or missile. Had we found such evidence, we would have immediately referred the matter back to the appropriate law enforcement agencies for their action. Let me state unequivocally, the Safety Board has found no evidence.
To the families of Flight 800, I would like to add this comment: It is unfortunate that a small number of people, assuming their own agendas, have persisted in making unfounded charges of a government cover-up in this investigation. These people do a grievous injustice to the many dedicated individuals, civilian and military, who have been involved in this investigation. Some 75 NTSB members have participated in this investigation. I pause while their names are listed on the screens in front of you.
These individuals, collectively, have more than 1,000 years of government and aviation industry experience. Many of them have served in the military, including service in Vietnam and the Gulf War. These men and women, in my opinion, represent the very best in United States government service. They are public servants all of us can be proud of.
I recognize that this TWA 800 investigation is technically complex, and that knowledgeable people can disagree over some substantive matters. But I take exception to those who consistently distort the record and persist in making unfounded charges of a cover-up. They do a disservice to all of us - but most especially to you, the families of the TWA 800 victims, who have suffered so much in this tragedy. And for that I am very sorry.
In its 33-year history, the Safety Board has earned a well-deserved reputation for independence, impartiality, honesty, and diligence. We have adhered to those values during this investigation, as we do in each investigation. The NTSB staff has the highest personal and professional integrity, and I assure you that we have done our very best to find the cause of this accident and to make recommendations that will prevent similar accidents from occurring in the future.
With that, Mr. Campbell, would you please introduce the staff for today's meeting.
Daniel Campbell: Good morning, Mr. Chairman, Members of the Board. I'll introduce staff at the front table and staff behind me will be introduced as they take part in the presentations. Working from my immediate right is Ronald Battocchi, agency General Counsel; Bernard Loeb, Director of the Office of Aviation Safety; Alfred Dickinson, who is the Investigator-in-Charge in the accident; James Wildey, who is the Metallurgy and Sequencing Group Chairman; Joseph Kolly, who did the Fire and Explosion Group work; Robert Swaim, who was Systems Group Chairman.
Dr. Loeb will begin this morning's presentations with an opening statement. Dr. Loeb has been employed at NTSB for 22 years and among assignments before becoming Director of Aviation Safety he served as the Director of the Office of Research and Engineering and as the Acting Director of our previous Bureau of Accident Investigation. He also has 15 years of prior private sector and government research experience, an undergraduate degree from Maryland University and his doctorate from George Washington in engineering and science. Dr. Loeb has twice received the presidential Distinguished Rank Award for his work as a senior government executive. Dr. Loeb.
Bernard Loeb: Thank you. Good morning, Mr. Chairman, Members of the Board. As you have just said, Mr. Chairman, the investigation into the crash of TWA Flight 800 has been the most extensive and encompassing aviation accident investigation the Safety Board has ever undertaken. It has truly been a monumental effort for everyone involved. Most people are aware of the lengthy underwater recovery operations and the large-scale reconstruction of the airplane fuselage and parts of the cabin interior that took place on scene in Long Island - and indeed, that massive effort symbolizes the extent to which this investigation has gone in leaving no stone unturned. Al Dickinson, the Investigator-In-Charge, will be discussing the on-scene portion of the investigation during his opening remarks. So I will not go into detail about that at this time.
What I am going to do is to summarize the significant findings of our investigation. This will just be an overview - more detailed explanations will be provided by the investigators during their individual presentations over the next two days. But I think an overall summary at this point would be valuable to put things in context.
First, we knew almost immediately after the accident that TWA Flight 800 had experienced an in-flight breakup. This was strongly suggested by the radar data - there was a loss of transponder returns and the primary radar returns indicated that pieces had departed the airplane and were fairly widely dispersed in the ocean. The wreckage recovery locations made it evident relatively early in the investigation that the in-flight break-up was initiated by an event in the area of the fuselage near the forward part of the center wing tank.
Specifically, pieces from the forward part of the center wing tank and adjacent areas of fuselage were recovered from the westernmost portion of the wreckage field (the portion of the wreckage field closest to JFK Airport from where Flight 800 took off). This first wreckage area is referred to as the "red zone." The recovery of the pieces from the red zone indicated that they were the first pieces to separate from the airplane. The nose portion of the airplane was found farther to the east, in what was labeled the "yellow zone," indicating that this portion of the airplane separated later in the breakup sequence. And most of the remaining wreckage was found in the easternmost portion of the wreckage field, farthest from JFK, which was labeled the "green zone."
This basic evidence - the radar data and the wreckage recovery locations - indicated that the airplane broke up in flight, and that the break-up initiated in the area of the fuselage near the forward part of the center wing tank.
On the basis of this initial information, we considered several possible causes for the initiation of the in-flight break-up:
· a structural failure and decompression;
· a detonation of a high-energy explosive device, such as a bomb or missile warhead; and
· a fuel air vapor explosion in the center wing tank.
We found no evidence that a structural failure and decompression initiated the break-up. A thorough examination of the wreckage by our engineers and metallurgists did not reveal any evidence of fatigue, corrosion, or any other structural fault that could have led to the break-up.
As a side note, I would like to mention that there was absolutely no evidence of an in-flight separation of the forward cargo door - one of the many theories suggested to us by the members of the public. The physical evidence demonstrated that the forward cargo door was closed and latched at water impact.
We also considered the possibility of a bomb or missile. However, high-energy explosions leave distinctive damage signatures on the airplane's structure, such as severe pitting, cratering, hot gas washing, and petaling. No such damage was found on any portion of the recovered airplane structure, and as you know, more than 95 percent of the airplane was recovered. Our investigators, together with many outside participants from the parties to the investigation, closely examined every piece of recovered wreckage. All of the participants agreed that none of the wreckage exhibited any of the damage characteristics of a high-energy explosion - that is, of a bomb or a missile.
Further, no missing portions of fuselage were large enough to represent the entry of a missile. You may have noticed that some of the photographs of the reconstruction show what appear to be several large missing areas, such as those that are shown on the screen now. However, almost all of the fuselage structure in these areas is actually attached to the adjacent pieces, but has been folded back or crushed in such a way that it does not cover its original area. Therefore, these large gaps that appear to exist in the reconstructed fuselage do not represent areas of damage that could have been caused by a missile.
In addition, we found no localized area of severe thermal or fragmentation pieces and no localized severe damage or fragmentation of the seats, such as would be expected if a high-energy explosive device had detonated inside the airplane. The injuries to the occupants and the damage to the airplane were fully consistent with an in-flight break-up and subsequent water impact. In light of all this evidence, a bomb or missile strike has been ruled out as an initiating event of the in-flight break-up.
The FBI did find trace amounts of explosive residue on three pieces of the wreckage. However, these three pieces contain no evidence of pitting, cratering, hot gas washing, or petaling, which would have been there had these trace amounts resulted from a bomb or missile. Further, these trace amounts could have been transferred to these pieces in various ways. For example, in connecting with ferrying troops during the Gulf War or during dog-training explosive detection exercises that were conducted on the accident airplane about one month before the accident. There is also the possibility that the explosive residues could have been deposited on the wreckage during or after the recovery operations as a result of contact with the military personnel, ships, and vehicles used during those operations. We don't know exactly how the explosive residues got there - but we do know from the physical evidence I've just discussed that the residues were not the result of the detonation of a bomb.
Unlike the other two scenarios I've just mentioned (a structural failure or a high-energy explosive), the third scenario we considered - a Jet A fuel/air explosion in the center wing tank - was consistent with the physical evidence. Specifically, as I've already mentioned, the wreckage recovery locations indicated that the first pieces to depart the airplane were from in and around the front of the center wing tank.
Based on these recovery locations and damage characteristics, the investigative group led by Jim Wildey (known as the Metallurgy and Structures/Sequencing Group) determined that the earliest event in the break-up sequence was an overpressure inside the center wing tank that caused structural failure of its forward section. This overpressure event started the break-up sequence that ultimately resulted in the destruction of the airplane.
I would like to emphasize that all of the parties to the investigation, as well as numerous outside experts and researchers, have agreed with the findings of the Sequencing Group.
Jim Wildey will be explaining the break-up sequence a little later today. The point I would like to make now is simply that the initial break-up sequence and early departure of pieces from in and around the center wing tank clearly indicate that the break-up was initiated by an overpressure inside the center wing tank. Given that there was no high-energy explosion in this (or any other) area, this overpressure must have been caused by a fuel/air explosion inside the center wing tank.
However, questions were raised early in the investigation about whether the conditions necessary for a fuel/air explosion could have existed inside the accident airplane's center wing tank, and also whether a Jet A fuel/air explosion could generate sufficient pressure to break apart the fuel tank and destroy the airplane.
To address the first issue, the Safety Board conducted flight tests at JFK in July 1997 using a 747 leased from Evergreen Airlines. Several test flights were conducted under conditions similar to those experienced by Flight 800. The fuel/air vapor inside the center wing tank was measured at various locations during the flights. The temperatures inside the center wing tank at the altitude at which the accident occurred (approximately 13,800 feet) ranged between 101 and 127 degrees Fahrenheit.
Extensive work done by scientists at the California Institute of Technology showed that Jet A fuel under the conditions experienced by Flight 800 would be flammable at these temperatures. In fact, their work demonstrated that fuel vapors under those conditions may have been flammable at temperatures as low as 96 degrees. Dr. Joseph Kolly will be talking more about this research later today.
The second issue - whether an explosion of Jet A fuel could generate sufficient pressure to break apart the fuel tank and destroy the airplane - was also put to rest in the investigation. Laboratory tests and quarter-scale tests under the direction of scientists at the California Institute of Technology demonstrated that pressures exceeding the structural limitations of the forward portion of the center wing tank were produced from the combustion of a Jet A fuel/air mixture similar to the one that existed in the center wing tank of TWA Flight 800.
Further, computer modeling of combustion in a full-scale tank confirmed that a localized ignition could generate pressure levels that would cause the damage we saw in the wreckage of the center wing tank from Flight 800. Finally, previous fuel/air explosions in the center wing tanks of commercial airliners that contained Jet A fuel have confirmed that a center wing tank explosion involving Jet A fuel can result in the destruction of an airplane. Specifically, I am referring to the November 1989 accident involving a Boeing 727 operated by the Colombian airline Avianca that occurred during the climb after takeoff, and the May 1990 accident involving a Boeing 737 operated by Philippine Air Lines that occurred on the ground at the airport.
The bottom line is that our investigation confirmed that the fuel/air vapor in the center wing tank was flammable at the time of the accident and that a fuel/air explosion with Jet A fuel was more than capable of generating the pressure needed to break apart the center wing tank and destroy the airplane. Together with the other physical evidence I have already mentioned, this leads to the inescapable conclusion that the cause of the in-flight break-up of TWA Flight 800 was a fuel/air explosion inside the center wing tank.
The next obvious question is: What ignited the flammable vapor inside the center wing tank and caused the explosion? Our Systems Group Chairman, Bob Swaim, has devoted the past four years to this question. He and his group considered every conceivable potential ignition source. They did exhaustive research and testing - much of it with help and participation from outside experts - to better understand some of these potential ignition mechanisms. As a result of this work, we determined that a number of possible ignition sources were very unlikely in this case.
It's important to note that ignition sources that were deemed unlikely under the circumstances of this case could be ignition sources under other circumstances. Bob Swaim and others will be prepared to further discuss these ignition sources later today if the Board has any questions about why they were deemed unlikely.
One ignition source that we could not deem unlikely, however, was that a short circuit involving electrical wiring outside the center wing tank somehow transferred excess voltage to fuel quantity indication system wiring leading to the center wing tank. Although the voltage in the fuel quantity indication system line is limited by design to a very low level, a short circuit from higher-voltage wires could allow excessive voltage to be transferred to the fuel quantity indication system wires and enter the fuel tank.
We cannot be certain if this in fact occurred, but of all the ignition scenarios that we considered, this scenario is the most likely. As I said, Bob Swaim will be telling us much more about this part of the investigation later today.
The accident airplane was 25 years old at the time of the accident. The electrical wiring that was recovered showed definite signs of deterioration and damage. One of the things that Bob Swaim and his Systems Group did was examine the condition of electrical wiring in numerous transport category airplanes of various ages from a variety of different operators. What they found was that cracked and damaged wire insulation, contamination of electrical wiring, and noncompliant wiring repairs could be found throughout the transport fleet, but were especially common in older airplanes. Therefore, the condition of the accident airplane was not atypical for an airplane of its age.
Although these types of conditions are common, they obviously increase the potential for short circuits to occur and, therefore, are a cause for concern. It became clear from our investigation that current maintenance practices do not adequately protect aircraft electrical wiring, especially with regard to older airplanes. In April of 1998, the Board issued six recommendations to the FAA, aimed at correcting several of the potentially hazardous conditions that we found on aircraft wiring. I am pleased to say that the FAA has taken action towards addressing all of those recommendations.
The potentially hazardous wiring conditions discovered in the context of this accident investigation have focused attention on the need to change maintenance practices, and to ensure that the integrity and safety of aging airplane systems is maintained. The FAA has begun to address these issues by developing an Aging Transport Non-Structural Systems Plan, and establishing a rulemaking advisory committee. These initiatives are still ongoing, so we do not yet know the final results of these programs. Our draft report outlines our concerns in this area and includes a recommendation to ensure that all of the issues identified by the FAA's plan are addressed. Of course, we will be following the FAA's progress on these issues with great interest.
Bob Swaim will be talking more about this part of our investigation tomorrow.
Our examination of the numerous potential ignition sources - and the recognition that many of these ignition sources cannot be reliably eliminated - led us to another concern: the adequacy of the current certification philosophy, which assumes that a flammable fuel/air mixture exists in fuel tanks at all times and attempts to preclude fuel tank explosions solely by eliminating all ignition sources.
We concluded that this approach is seriously flawed because experience has demonstrated that all possible ignition sources cannot be reliably eliminated and, further, it is not rational to believe that we can predict all possible ignition sources. Therefore, the most effective approach to preventing fuel tank explosions is to eliminate flammable vapors inside fuel tanks in addition to attempting to eliminate ignition sources.
The results of the flight tests and the flammability research I discussed earlier are especially significant because they indicate that many commercial aircraft may routinely operate with flammable fuel/air vapor inside their fuel tanks. In particular, airplanes that have air conditioning packs located directly beneath their center wing tanks are especially likely to operate with flammable vapor in those tanks because of the large amount of heat generated by these packs.
The FAA has recognized this, and has proposed rulemaking that would preclude the use of such designs in the future, unless the design includes a means for reducing the transfer of heat to the fuel tank. One of the concerns we have, however, is that not enough has been done to reduce flammability in existing designs in the current fleet.
This accident would not have occurred but for the flammable vapor in the center wing tank, and we believe that perhaps the most valuable lesson that can be learned from this accident, and our best hope for preventing similar accidents in the future, lies in recognizing this fact.
The draft report that you have before you does not propose any new recommendations to address fuel tank flammability. But as you know, the Safety Board already recommended in December 1996 that the FAA preclude the operation of transport-category airplanes with explosive fuel/air mixtures in fuel tanks. The Board specifically asked the FAA to consider airplane design modifications, such as fuel tank inerting systems that would make the fuel/air mixture nonflammable. In addition to this long-term recommendation, the Board also asked the FAA to require more immediate, short-term changes - specifically, to require modifications in operational procedures that would reduce the potential for flammable fuel/air mixtures in fuel tanks.
As I just mentioned, the FAA has initiated rulemaking aimed at minimizing fuel tank flammability in newly designed airplanes. In addition, the FAA is also evaluating the use of directed ventilation to cool the center wing tank area, the use of ground-conditioned air instead of air conditioning packs when an airplane's on the ground, and fuel tank inerting systems both on-board for future design and ground-based for the existing fleet. Each of these approaches has some benefit to the existing fleet. But at this time, fuel tank inerting appears to be the most promising method for dramatically reducing fuel tank flammability in both future designs and in the existing fleet.
In addition to our concerns about fuel tank flammability, this investigation and several others have brought to light some broader issues regarding aircraft certification. For example, there are questions about the adequacy of the risk analyses that are used as the basis for demonstrating compliance with many certification requirements. We believe that the certification approach could be improved by requiring a reliable, independent means for overcoming or counteracting any potential failure that could cause catastrophic results, regardless of the calculated probability of that failure.
Although those issues are raised in the draft report on this accident, they are not examined in depth. However, we believe these would be appropriate issues to explore in depth as part of the Board's upcoming safety study on aircraft certification.
The final topic that we will address is the reported witness observations. In particular, we will discuss the 258 witnesses who reported seeing a streak of light. There has been a persistent belief by some (outside the investigation) that the streak of light reported by these witnesses was a missile attacking the airplane. As I have already explained, the physical evidence indicated indisputably that a missile did not strike the airplane.
Nonetheless, because of the media attention and public interest in these witness reports, we analyzed all of the witness documents in great detail in an attempt to understand what the witnesses may have seen. We studied all 736 witnesses for whom we had documentation, including those who reported seeing a streak of light.
As Dr. David Meyer will explain in more detail during his presentation tomorrow, almost all of the witness accounts are consistent with their having observed some portion of the accident sequence. In particular, after the center wing tank explosion and the separation of the nose portion a few seconds later, the airplane continued in its crippled flight for roughly 30 seconds or more, during which time burning fuel from the damaged airplane likely appeared as a streak of light. A small portion of the reported witness observations (56 of them) were not completely consistent with the airplane's flight path. However, these accounts can also be explained in a number of different ways and, as I said, Dr. David Meyer will be discussing all of this in much greater detail tomorrow.
In closing, I would like to reiterate that the physical evidence irrefutably indicated that the first pieces to depart the airplane were from the forward part of the center wing tank; that there was no physical evidence of a bomb or missile strike, but rather of an overpressure event inside the center wing tank; and that research, tests, and previous accidents demonstrate beyond any doubt that the overpressure was the result of a Jet A fuel/air vapor explosion in the center wing tank.
The safety issues in the accident relate to fuel tank flammability, potential ignition sources, and maintenance and aging of aircraft electrical wiring. I think aviation safety will best be served if we can focus our attention primarily on those issues.
This concludes my remarks. Mr. Al Dickinson will address the on-scene portion of the investigation, followed immediately by Mr. Jim Wildey, who will be discussing the break-up sequence of the airplane, and then staff will be prepared to answer any questions that the Board Members may have.
Jim Hall: Before you introduce Mr. Dickinson, let me mention to the Board that we all have in front of us a proposed agenda. The agenda includes Mr. Dickinson's presentation and a presentation on the break-up sequence by Mr. Wildey that will be followed by questions and answers on that issue as well as a presentation on fuel tank flammability and potential fuel tank ignition sources by Mr. Kolly then Mr. Swaim.
We hope to complete those presentations today. That will call for a discussion of the maintenance and aging of aircraft systems, design and certification issues, and the report of witness observations, followed by the Board's consideration of the conclusions, probable cause, and recommendations that are proposed by staff.
Are there any objections, additions, or deletions from the Board Members to this agenda?
We will then proceed, and I'll ask Dr. Loeb if he will introduce Mr. Dickinson for his presentation.
Dr. Bernard Loeb: Mr. Dickinson has served as IIC and as a U.S.-accredited representative in numerous aviation accidents and incidents. He has been a member of the Army Reserves and National Guard for more than 20 years. Mr. Dickinson holds a commercial pilot's license and has logged more than 5,000 hours flight time in both airplanes and rotary wing aircraft. He is a recipient of the Aviation Week and Space Technology Laurel Award from February 1997 granted to the investigation team in recognition of their work on TWA 800. He has an aerospace engineering degree from the University of Southern California.
Jim Hall: IIC, for those who may not be familiar with that term, is our Investigator-in-Charge of this particular investigation. Please proceed.
Al Dickinson: Good morning Mr. Chairman, Board Members, and staff. Today I will discuss the launch of the Go-Team, the Safety Board personnel involved in the investigation, the Navy involvement in the recovery, the mock-ups and partial reconstruction of the wreckage, and the parties involved in the investigation of TWA Flight 800.
On July 17, 1996, at dusk, TWA Flight 800, a Boeing 747-131, crashed into the Atlantic Ocean near East Moriches, New York. The aircraft was a scheduled air carrier flight operated under Title XIV Code of Federal Regulations, Part 121, from New York to Paris. All 230 people on board were killed in the accident.
The flight departed the John F. Kennedy International Airport at 8:19 PM from runway 22-Right. Visual meteorological conditions prevailed, and an instrument flight rulesflight plan was filed. Air traffic control communications with Flight 800 were routine, and the last transmission from Flight 800 was at 8:30 and 19 seconds, when the flight crew acknowledged a clearance to 15,000 feet. About one minute later, Flight 800 disappeared from radar.
I was notified that the airplane was missing about 8:50 PM. While the Go-Team was being assembled in Washington, investigators from the NTSB's regional office in New Jersey went immediately to the scene of the accident. The headquarters Go-Team arrived on-scene early the next morning. The initial Go-Team consisted of myself, a deputy senior IIC, and investigators in the areas of systems, structures, powerplants, survival factors, and air traffic control. The team was accompanied by former Safety Board Vice Chairman Robert Francis, as well as members of the Safety Board's Office of Government and Public Affairs.
We arrived at the Coast Guard station in East Moriches, shown above, at about 7:30 on July 18, 1996. Normally, the Coast Guard station is manned by about five people on duty; however, 48 hours after the accident, over 30 agencies and 2,500 people had converged on the facility.
Due to the magnitude of this investigation, more than one NTSB investigator was assigned to many of the groups, and as the investigation progressed, several new groups were formed - to date, over 22 groups have participated, by far the most groups ever to participate in an investigation in the Safety Board's history. Safety Board staff assigned to the investigation included
I was designated as the Investigator-in-Charge. Deputy IIC - Bob Benzon; Systems - Bob Swaim; Electromagnetic Induction - Scott Warren; Structures - Deepak Joshi, assisted by Alex Lemishko; Airplane Interior Documentation - Hank Hughes; Witness Groups - David Meyer, Dana Sanzo, Norm Wiemeyer, Doug Brazy, and Heather Knapp; Data Management - Deborah Bruce and David Meyer; Radar - Charlie Pereira and John Schade; Flight Data Recorder - Dennis Grossi; Cockpit Voice Recorder - Jim Cash; Metallurgy and Structures/Sequencing - Jim Wildey assisted by Frank Zakar; Reconstruction - Larry Jackson; Meteorology - Greg Salottolo; Hazardous Materials and Security - Tom Lasseigne; Medical Forensic - Burt Simon; Fire and Explosion - Joseph Kolly and Merritt Birky; Powerplants - Jim Hookey; Air Traffic Control - Al Lebo; Operations - Norm Wiemeyer; Aircraft Performance - Dennis Crider; Airport Security - Larry Roman; Trawling - Charlie Pereira and Doug Brazy; Flight Test - Robert Benzon and Dan Bower; Visibility - David Meyer assisted by Dana Sanzo; Report Writers - Jodi Moffett and Karen Bury; and Editor - Kristen Sears.
These are just a few of the various groups formed to investigate different aspects of the crash. Additionally, many other Safety Board staff members provided support to the investigation.
The Safety Board requested the assistance of the Supervisor of Salvage of the U.S. Navy for the recovery of the victims and the aircraft wreckage. The Navy recovery vessels were on-scene within two days, and by the time they completed the effort, over 95 percent of the 400,000 pound aircraft and remains of all of the 230 people aboard had been recovered. The Navy was assisted by the U.S. Coast Guard, Oceaneering, Underwater Search and Survey, the National Guard, and the National Oceanographic and Atmospheric Administration, as well as dive teams from Suffolk County, New York City and State Police, Fire Department personnel from both Suffolk County and New York City, and the FBI.
The cockpit voice recorder and flight data recorder were recovered by Navy divers on July 24, 1996. Both contained good quality data and revealed a routine flight until ending within a fraction of a second of one another at about 8:31 and 12 seconds.
After the aircraft wreckage was recovered from the ocean, it was transported to an abandoned Navy facility in Calverton, New York. The wreckage was documented and thoroughly examined and tested for chemical residues by the FBI - both on the recovery ships, at the dock, and again in the hangar. The hangar floor was marked and the wreckage laid out as to its position on the aircraft.
As pieces of wreckage were identified as being recovered from areas closest to JFK, and therefore assumed to have departed the airplane the earliest in the break-up sequence, they were placed on an initial mock-up, which is shown above. To further understand the accident, a three-dimensional reconstruction including the structure around the center wing tank from just after the cockpit to the forward portion of the aft cargo department was started.
The planning started in September of 1996 for the actual truss being constructed in February of 1997 and finishing over two months later in April. The 93-foot reconstruction - the largest wide body in the world - took over two months to construct, and contains over 870 pieces of wreckage weighing over 60,000 pounds. Metallurgists from the Sequencing Group thoroughly investigated each piece of aircraft, examining holes and penetrations and conducting a sequence study to determine the sequence in which the pieces came off the aircraft. Additionally, the Fire and Explosion Group used the reconstruction to map soot and fire patterns.
While the wreckage was being recovered, the Maintenance Group assembled in Kansas City, Missouri, to review the maintenance records of the aircraft. The airplane, which was manufactured in July of 1971, was purchased new from the Boeing Company by TWA. The Maintenance Group reviewed all maintenance records from the date of manufacture until July 17, 1996. The records indicated that TWA had accomplished mandatory directives, maintained scheduled maintenance, and maintained a continuous airworthiness maintenance program on the accident aircraft. The records indicated that the airplane was in compliance with all applicable airworthiness directives. Prior to the accident flight, routine periodic service was accomplished at JFK International Airport.
The Safety Board leverages its technical expertise with assistance from parties to the investigation. The parties to the TWA 800 investigation were: the Federal Aviation Administration; the Boeing Commercial Airplane Group; Trans World Airlines; the International Association of Machinists, Aerospace Workers, and Flight Attendants; the Air Line Pilots Associations; the National Air Traffic Controllers Association; Pratt and Whitney; Honeywell; and the Crane Company, Hydro-Aire.
During this extended investigation, there have been countless meetings and weekly telephone conference calls to provide for an open exchange of information and ideas and to keep all of the parties informed as to the progress of the investigative groups. During all of these discussions, the parties were asked to provide their comments on the scope of the investigation. Additionally, as normal Safety Board practice, following the technical review, the parties were asked to provide submissions to the Safety Board on our analysis of the factual evidence, findings, probable cause, and recommendations.
Submissions were received from: the Boeing Commercial Airplane Group; Trans World Airlines; the International Association of Machinists, Aerospace Workers, and Flight Attendants; the Air Line Pilots Association; and the Crane Company, Hydro-Aire. All of the parties have agreed with the findings in our report that the explosion initiated within the center wing tank of the accident airplane. Although the IAM agrees with our findings, they feel that the explosion of the center wing tank was preceded by an unspecified event.
Additionally, the investigation has utilized a variety of resources, including: NASA; Sandia National Laboratories; the University of Nevada, Reno; Applied Research Associates in Denver; Brookhaven National Laboratories; the California Institute of Technology; Wright Laboratory at Wright-Patterson Air Force Base; the Naval Research Laboratory; the United States Naval Air Warfare Center in China Lake, California; Britain's Defense Evaluation and Research Agency; and the Christian Michelson Research Institute in Norway. Combustion Dynamics, Ltd. was also included.
Under the rules of International Civil Aviation Organization, air safety investigators from the United Kingdom, France, Singapore, Australia, Canada, and New Zealand participated in the investigation as technical observers.
Mr. Chairman, this concludes my statement. I will be followed by Mr. Jim Wildey, who will talk about the extensive work done to determine the sequence of events.
Jim Hall: Let's proceed then with Mr. Wildey's presentation and then we'll have a short break before we take questions from the Board on the two presentations.
Dr. Loeb: Mr. Wildey has been employed at the Safety Board in the Materials Laboratory Division for about 25 years. He has been Chief of the Laboratory for a little more than two years. Mr. Wildey has participated in many of the major accident investigations involving component or structural failures investigated by the Safety Board. Mr. Wildey was involved in the 1985 Indian Airlines Boeing 737 bombing, the 1988 Aloha Airlines 737 structural failure, and the 1988 Pan Am 103 bombing in Lockerbee, Scotland, just to mention a few. Mr. Wildey has been the recipient of the NTSB Chairman's Award and the recipient of the Aviation Week and Space Technology Laurel Award, in February 1998, in recognition of his analysis of the break-up of the TWA 800 airplane. Mr. Wildey possesses a bachelor's degree in Metallurgical Engineering from Virginia Polytechnic Institute and State University. Mr. Wildey.
Jim Wildey: Thank you. Good morning, Mr. Chairman, Members of the Board. My presentation is on the in-flight break-up of the TWA Flight 800 airplane, and how it was determined that the break-up initiated from an overpressure event within the center wing tank.
As part of an introduction, I will discuss the formation of the Metallurgy and Structures/ Sequencing Group and how we did our work and will give a description of the wing center section in the center wing tank structure. The overall break-up sequence will then be presented, with detailed information on specific portions of the break-up sequence as well as the evidence that led to the conclusion that the break-up was initiated from an overpressure event. My presentation will finish with a short video of the reconstructed portion of the accident airplane, showing the break-up sequence.
To address the question of how the airplane broke up, the Board formed what was titled the Metallurgy and Structures/Sequencing Group, with group members from the major parties to the investigation. Representatives from the FBI also monitored the Group's investigation, but did not participate in the generation of our reports. Our task was to find out how the airplane broke apart and where the break-up initiated so that investigation efforts could concentrate on the cause of the break-up.
Starting in December of 1996, the Group spent many weeks examining the structural pieces after they were recovered from the ocean and transported to the facility at Calverton. As each piece of the recovered wreckage was brought to the hangar facility, it was initially examined by bomb explosion experts with the FBI and ATF [Bureau of Alcohol, Tobacco, and Firearms] as well as by Safety Board and FBI metallurgists for characteristic evidence of the detonation of a bomb or missile warhead. Simply stated, none of the pieces had this evidence.
All of the major structural pieces, and many of the smaller pieces, were labeled with their tag number and recovery area and examined by the Structures Group to determine what part of the airplane they came from. Once they were identified, the pieces were laid out on a two-dimensional grid on the hangar floor.
The photograph we are looking at now shows most of the fuselage section laid out on the two-dimensional grid. The nose of the airplane extends toward the hangar door at the top of the picture, and the tail is toward the lower left. The inside surfaces of the pieces are facing up. Not shown in this picture are the areas containing the layouts for the wings, for the tail section, for the engines, and for the cabin interior. Also visible here are some of the smaller-scale, three-dimensional reconstructions that were made of portions of the wing center section.
The Sequencing Group did a large portion of its examinations on the structure as it was located on the two-dimensional grid and on the smaller-scale three-dimensional reconstructions.
As Mr. Dickinson discussed, in the spring of 1997, investigators assembled a 93-foot long, three-dimensional reconstruction of the center portion of the airplane's fuselage from just after the cockpit to within the aft cargo compartment. The reconstruction included all of the wing center section, the main landing gear bay, and the furthest in-board pieces of the wing. All of the fuselage and wing center section pieces that were recovered from the red zone were a part of this reconstruction.
This photograph shows an overall view of the right side of the reconstructed portion of the airplane. The structural pieces of the airplane were attached to an iron beam truss that extended in the main cabin space between two support columns. The Sequencing Group used this reconstruction to verify earlier conclusions and to more easily compare fire and soot accumulation patterns. The initial examination showed that there was a relatively clear demarcation between the pieces that were found in the red, yellow, and green zones.
This model gives a rough idea of the recovery locations of the various portions of the airplane. The first structural pieces found along the flight path were the pieces recovered from the red zone. These pieces included a ring of fuselage structure from in front of the wing center section, structure from the aft end of the forward cargo compartment, and pieces of the wing center section itself.
Other items recovered from the red zone included: the forward portion of the keel beam, which is located under the wing center section; main cabin floor beams; and the two forward air conditioning packs. Any viable break-up sequence had to account for the early release of these red zone parts from the remainder of the structure.
At the conclusion of our efforts, all the Sequencing Group members agreed that the physical evidence contained on the recovered pieces showed that the break-up initiated within the wing center section, at spanwise beam 3. This beam is the most forward boundary member of the center wing tank. The pieces ejected as part of the initial overpressure event contained at most minor soot accumulation, indicating that some type of combustion was associated with the initial overpressure event. However, the lack of significant soot on these red zone pieces shows that there was no severe fire before the overpressure event.
I would like to spend a few minutes to describe the important elements that make up the wing center section on a 747-100 series airplane. The wing center section of the airplane visible here in the center of the model is designed to carry the wing loads through the fuselage and to support the fuselage on the wings.
This is a model of the wing center section, oriented the same way as the airplane shown on the previous slide. The wing center section is a large box structure with a footprint about the size of a two-car garage. The wing center section extends between the front spar and the rear spar. Also found here are the main cabin floor beams, which serve to stiffen the upper skin panel of the wing center section. Internally, the wing center section is divided into compartments by a series of lateral, or spanwise, beams. The center wing fuel tank occupies most of the wing center section, extending from the rear spar to spanwise beam 3, which is just behind the front spar.
I'll also mention some of the other structural members and systems associated with the wing center section. The keel beam is located along the bottom center line of the airplane. This beam extends from the aft end of the forward cargo compartment under the wing's center section, through the landing gear bays, and to the forward end of the aft cargo compartment. The keel beam acts to transfer fuselage loads under the wing center section. Also, the 747 has three air conditioning packs that are located below the wings. Dr. Kolly will discuss these packs and their relationship to heating of the center wing tank.
This is a drawing of the wing center section viewed from the right side with the upper skin removed. The structural members of the wing center section are identified, including: the rear spar, spanwise beam one, the mid spar, spanwise beam two, spanwise beam three, and the front spar. There is also a center line rib that extends between the rear spar and the mid spar. These internal beams and ribs provide stiffening and reinforcement to the upper and lower skin panels of the wing center section. As I previously indicated, the center wing tank, here shaded darker, occupies most of the wing center section on a Boeing 747-100 series airplane. The forward portion of the wing center section, between spanwise beam 3 and the front spar, is an unpressurized dry bay that does not carry fuel.
As a final item, please note the location of the large storage bottles for drinking water carried on the airplane. These bottles are located at the center of the forward side of the front spar.
This photograph shows a view of the right side of a reconstructed portion of the airplane. Coloration has been added to correspond to the recovery positions of the structure from the red, yellow, and green zones You can see in this photograph a distinct band of red zone fuselage parts.
This photograph shows a closer view of the red zone area on the right side of the reconstructed portion of the airplane. Most of these red zone pieces, which were the first pieces to depart the structure, were located in front of the front spar, whose location is indicated.
How did our group determine the break-up sequence? We began by examining portions of the structure in great detail. Localized, sequenced segments were then developed based on the observable features in each portion. Eventually, individual sequence segments were combined until a cohesive and comprehensive break-up sequence, consistent with the overall body of evidence, was generated. We also used stress analysis to provide confidence that proposed scenarios were consistent with structural properties and expected failure modes.
Based on our detailed examinations of the structure, and supported by the results of stress calculations, the Sequencing Group determined that the break-up of the airplane initiated with the fracture of spanwise beam 3 at its upper end. We found that the separated beam rotated forward and impacted the front spar.
This drawing shows an overall right side view of the wing center section, depicting how spanwise beam 3 rotated forward. Also, the various members of the wing center section have been color-coded to reflect their recovery positions. Note that most of spanwise beam 3 and the front spar are red, indicating their early release from the structure.
As spanwise beam 3 rotated forward, it created impact marks in two locations: first, on an upper skin panel stiffener, located just forward of the upper end of the beam; and second, on the aft side of the front spar. The locations of the two sets of impact marks will be illustrated on this drawing, which shows the forward portion of the wing center section as viewed from the right side. The location of the front spar is shown in its normal position. Spanwise beam 3 is shown both in its normal position with dash lines and in a rotated position with solid lines. This red arrow indicates the location of one set of impact marks on the aft side of a stiffener for the upper skin panel. This second red arrow indicates the set of impact marks on the aft side of the front spar. The fracture and the resulting forward rotation of spanwise beam 3 were consistent with overpressure on the aft side of spanwise beam 3 within the center wing tank.
I also have a video describing the fracture of spanwise beam 3 and the creation of the impact marks on the aft side of the front spar. The video was taken from the right side of the reconstructed portion of the airplane, where we'll be looking first into the fuel tank bay behind spanwise beam 3, then into the dry bay between spanwise beam 3 and the front spar. Forward will be to the right as we view the video.
"I'm standing in the fuel tank of the 747, just behind spanwise beam 3. This beam is the most forward member of the fuel tank. The very first event identified by the Sequencing Group was an explosion of the fuel air vapor inside the tank. This explosion forced spanwise beam 3 forward, fracturing the stiffeners on the back side of the beam and across the top of the beam. Spanwise beam 3 rotated forward and impacted another stiffener just in front of it as the roof lifted up, and then spanwise beam 3 continued to rotate forward and impacted the aft side of the front spar just in front of this.
"This is a dry bay between spanwise beam 3 and the front spar. After spanwise beam 3 separated across the top, pressure behind spanwise beam 3 forced it forward and it rotated. The top end of spanwise beam 3 struck the aft side of the front spar and it left behind these very distinctive witness marks, and those marks extended pretty much all the way across the front spar, indicating that all of spanwise beam 3 was rotating forward."
I have described so far the fracture of spanwise beam 3 and its impact on the front spar. Following the impact from spanwise beam 3, the front spar fractured at its upper end, cracking progressed down the front spar, and fuselage cracking initiated at stringer 40 right.
The cracking in the lower fuselage is illustrated in this schematic drawing. We are looking down and aft on the lower internal portion of the fuselage skin in the area forward of the front spar. The grid pattern represents the location of the internal structure. The initiation area of the fuselage skin cracking, which is along stringer 40 right, is indicated. After cracking initiated in the fuselage at this location, it quickly spread through the lower fuselage along the positions indicated by the dark red lines drawn on the structure.
Based on deformation patterns, the fracture, as indicated by the dark red lines, occurred earlier than any other fuselage fractures in the entire airplane. The direction of cracking along these early fractures was determined by specific features associated with the rivet-to-rivet fracture pattern of the fuselage skin in these areas. This rivet-to-rivet fracture pattern was established by detailed examination of every inch of these early fuselage cracks.
The blue arrows on the red fractures show how these early fractures stemmed from the initiation site at stringer 40 right adjacent to the front spar. The early fuselage cracking shown here propagated primarily under the normal pressure differential between the interior of the fuselage and the outside air at 13,800 feet. These early fractures generated a large hole in the belly of the airplane, through which structure and interior components would have been injected.
At this point in the sequence, spanwise beam 3 has fractured and impacted the front spar, and the front spar cracking has spread through the forward of the front spar. After loss of the belly structure, fractures progressed up the sides and across the top of the fuselage, until the nose portion of the airplane was completely separated.
The damage that I have described so far is the extent of the damage created as a result of the initial overpressure event, and I would like to provide some overall perspective regarding the speed of this portion of the sequence. Even though it has taken me several minutes to describe it, I would emphasize that this portion of the sequence occurred very quickly, within only a few seconds.
Before presenting the remainder of the sequence, which occurred over many more seconds, I would like to summarize the evidence that led to the conclusion that the break-up of the airplane was initiated by an overpressure event. First of all, we determined that spanwise beam 3 fractured at its top and rotated forward. These features are indicative of excessive pressure on the aft side of spanwise beam 3. Calculations indicate that a pressure differential of about 25 pounds per square inch across this beam would initiate the beam's fracture. In addition, the calculations show that spanwise beam 3 is the weakest of the boundary members of the center wing tank.
We also found that the upper skin panel was bulging upward as spanwise beam 3 was separating. This upward bulging was determined by the pattern of the impact mark created by the upper end of spanwise beam 3 as it struck the stiffener immediately forward of the beam's upper end. This upward lifting of the skin is also indicative of excessive pressure within the center wing tank.
We found that the front spar bulged forward in two lobes, restricted by the inertial resistance of the water bottles mounted at the center of the spar on its front side. This bulging is an indication of the escaping overpressure within the center wing tank acting on the aft side of the front spar.
The group also determined that a downward pressure load on the lower skin panel of the wing center section reacted through the keel beam and was the primary source of the stress that initiated cracking in the fuselage at stringer 40 right.
The examinations of the structure showed that the break-up began with the fracture of spanwise beam 3, and the features I have just mentioned clearly show that the fracture of spanwise beam 3 initiated from an overpressure event within the center wing tank of the 747 airplane.
I will now continue with the break-up sequence after separation of the red zone pieces, as previously described.
This photograph is a repeat of an earlier slide. The nose portion, here on the right and colored yellow, separated as a result of the loss of initial pieces, here colored red. After separating from the remainder of the airplane, this nose portion remained intact all of the way to water impact. I would like to point out the heavy compression, crushing, and break-up damage found on the lower and right sides of the nose portion. The location of this heavy damage indicates that the nose portion impacted the water relatively flat, but rolled slightly to the right. The forward cargo door, located on the lower right side of the nose portion, contained damage very similar to the neighboring pieces of the fuselage. This is a clear indication that the door was in place when the nose portion impacted the water.
The major portion of the airplane, here on the left colored green, also remained intact for a period of time after separation of the red zone pieces and loss of the nose. This portion of the airplane contained both wings, most of the wing center section, which extends between the arrows, as well as a limited amount of fuselage structure in front of the wing's center section.
Aerodynamic considerations and radar returns indicate that the major portion of the airplane climbed and rolled, then began a steep descent to the water. As speeds and loads built during the descent, the wings separated at the outboard engines and the wing center section failed adjacent to the left wing. Fire and soot patterns were concentrated on the inboard end of the right wing and on structure that remained attached to the right wing during the descent.
Fuel escaping from the right wing was a major source of the fuel for this fire. These fire and soot patterns assisted in the determination of portions of the sequence.
This completes my description of the break-up sequence. To summarize, I have a short video presentation. This video again was shot at the reconstructed portion of the airplane, and hopefully the video will be the next best thing to having the reconstruction here with us. The video shows the right side of the airplane, and forward is to the right.
"The break-up sequence of the TWA Flight 800 airplane began with the explosion of fuel/air mixture within the wing center section fuel tank. Pressure from this explosion fractured the front member of the fuel tank, spanwise beam 3, along the top. Spanwise beam 3 rotated forward and impacted the aft side of the front spar. Cracking in the front spar came downward and entered into the fuselage. This fuselage cracking progressed around three sides of a large piece of belly structure. This created a hole through which pieces of the front spar, spanwise beam 3, and one piece of spanwise beam 2, were free to be ejected from the airplane.
"Fuselage cracking progressed upward on both sides of the hole, and very quickly, a ring of fuselage material completely separated from the airplane. This allowed the nose portion to fall and hit the ocean surface in one piece. The bulk of the airplane, the major portion of the airplane, remained intact for a period of time, eventually breaking apart further downrange, and fell into the ocean in several pieces."
In conclusion, I can say that the Sequencing Group found that the break-up of the TWA Flight 800 airplane initiated with the fracture of the forward boundary member of the center wing fuel tank as a result of an overpressure event within the tank. Furthermore, the vast majority of the features documented by the Sequencing Group were not consistent with any other proposed scenario for the break-up of the airplane.
Jim Hall: Thank you, Mr. Wildey. What I would propose to the Board, since we have been sitting here along with the audience for approximately an hour and a half and I know we have many questions for Mr. Wildey and Mr. Dickinson, I suggest we take a 15-minute break and then we will reconvene this Board meeting.
After Break:
Jim Hall: We will reconvene this meeting of the National Transportation Safety Board. The Board is in the midst of our deliberations and discussion of an aviation accident report that is carried as Board's notation 6788G, an in-flight break-up over the Atlantic Ocean of Trans World Airlines Boeing 747, that occurred off the coast of East Moriches, New York, on July 17, 1996.
The Board's program has included an introduction and general overview by Dr. Bernard Loeb, and then a discussion of the on-scene accident investigation recovery by Mr. Dickinson, followed by a discussion of the break-up sequence by Mr. Wildey. These Board proceedings are being carried worldwide on the Board's Internet site, www.ntsb.gov, as well as on C-SPAN.
In addition, I would like to thank the Department of State for providing two individuals who are interpreters for our French families. You may see them in the booth that is indicated to my left to the rear of the Boardroom. I spoke with the interpreters on the break and they requested that, to the extent possible, if all of us could speak a little slower, it would assist them in being sure that the interpretation for the French families is accurate and that they get all of the information that we are trying to cover in this material.
Mr. Wildey, I would ask at the beginning if you would please stand up so that the individuals in the room could see how tall you are. How tall are you, Jim? Six feet seven. I wanted to be sure to put in perspective the film and video you saw of Mr. Wildey in the center tank and in the video.
Mr. Wildey, I think it would be helpful if you could quickly give us again the relationship of the recovery positions of the pieces and the determination of the sequence to set us up for our questioning.
Jim Wildey: Well, we certainly used the recovery positions of pieces from the ocean to initiate our group. Having said that, however, the recovery positions and the determination of the sequence are really independent. We would have come up with this break-up sequence regardless of where the pieces were found. That's based on the damage patterns and the types of fractures and all the witness marks and things like that that were documented. So even though we started with the recovery positions and the assumption that these red zone pieces must have been the first pieces to come out, the conclusions that we reached were really independent of the fact that we started with that as a baseline.
Jim Hall: I ask that because there have been some allegations made that the recovery pieces were not properly identified and marked. Mr. Dickinson, could you tell us a little bit about how we went with the FBI in putting together the recovery from the ocean of this very, very large aircraft and, obviously, if you could just sketch that for us and what was done in the early days of the investigation?
Al Dickinson: Yes, sir. We coordinated with SUPSAL, the Navy contingent; actually it was Captain Chip McCord, who coordinated with me the first day that we got there. And I remember him telling me that it would take a couple of days to get the assets there and first he was going to survey the whole area, which involved getting all the other boats that were in the area out of the area because they were towing a side scan sonar over the whole area to determine where the wreckage was. After they did that for a couple of days, they also attempted to locate the CDR and the FDR using the pinger system, but it was not recovered in that effort. Apparently, those transmitters were shielded by the wreckage. The Navy stayed on-site for three months after we initially found all the wreckage in the different zones, and we organized a system where we recovered pieces and tagged them with different locations and brought them back into Calverton for the reconstruction.
Jim Hall: The first part of the wreckage that was recovered, obviously, was floating. Do we have any idea how much percentage-wise of the aircraft was taken off of the surface of the water initially?
Al Dickinson: It was a small percentage, Mr. Chairman. We don't know the exact amount.
Jim Hall: Some of that was brought and turned over to the FBI, and it was clearly floating, and we couldn't identify that to a specific zone until possibly a best guess situation.
Al Dickinson: Exactly.
Jim Hall: Mr. Wildey, there's also been some question as to the airplane itself when the nose departed. Why did it pitch up? Why did the airplane go up?
Jim Wildey: That's an aerodynamic and a performance consideration. I guess Mr. Crider would be best for that.
Bernard Loeb: Let me try to answer that. The airplane pitched up simply because gravity shifted aft when the nose came off. It's just a simple matter of physics. When the nose came off, the weight from the front end of the airplane and the CG, the center of gravity, shifted aft. It would be just a natural thing. It's physics. There's nothing exotic about it or mysterious.
Jim Hall: The aircraft, it was pointed out, was 25 years old. Was there any fatigue, cracking that contributed to the break-up of the aircraft. If this event had occurred on a newer aircraft, do we think we would have had the same sequence? I understand that requires some speculation on your part, but I'm trying to get into some basic, common-sense questions that some of the family members and others have.
Jim Wildey: There were some fatigue cracks that were found on the airplane, and these have been documented and are contained in our report. However, it's clear and the Sequencing Group determined that the location of these fatigue cracks and their presence played no role in either the location of the initial fractures or the sequence of the break-up.
Jim Hall: If we could put up one of the side views of the aircraft that shows those large holes on the side of the aircraft.
Jim Wildey: That could be one of Dr. Loeb's, or my number 10 would be a good one.
Jim Hall: That's fine. That's a little distant view. But as we look at that, Mr. Wildey, there's obviously pieces of the structure missing. We know that we were able to only recover, despite all of our efforts, approximately 95 percent of the aircraft, which I may say is probably the largest under-ocean recovery of an aircraft in aviation history. Is it possible that an evidence of a bomb is only on the small portions of the structure that was not recovered or identified?
Jim Wildey: First of all, I will point out that, as Dr. Loeb said, the holes that you see here aren't really holes. The structure, especially the two big ones you see on the right side and then center left - those holes, if you call them that, are totally filled by structure that's folded in or crushed. As for the possibility that the evidence of an explosive device might have been contained on the missing structure, experience has shown clearly that the evidence of an explosion is contained through a larger volume than just a relatively small area. They've done the Lockerbee history and other explosions that the Safety Board has been involved in. So therefore it's very, very unlikely that the small amount of structure that's missing, which is from various areas spread throughout the airplane, could have been the only pieces that could have contained the evidence of a bomb or a missile explosion.
Jim Hall: On page 185, again, being slightly redundant on the subject of the report, you speak on lines 5 and 6 about the apparent hole that was 2 to 3 feet longitudinally and about 5 feet circumferentially. Would you again tell me how you know that you had most of that fuselage skin there, in terms of that particular hole, the largest hole on the aircraft?
Jim Wildey: Actually, I don't believe that's the largest one. In fact, we don't have a view of that. It's on the left side and most of our views are from the right side. And that hole is not untypical of some of the other holes. The structure is actually there. It's folded and bent and deformed inward in various ways. This particular hole that you mention in the report is from the left wing upper side at the aft end of the wing, where that structure is connected to the wing's center section. We determined that one of the events that occurred was the fracture of the wing center section adjacent to the left side, adjacent to the left wing, and as part of that motion that created this hole as it came upward and inward. It would have been where the hole is now. So we believe that that was the failure of the left wing as it came upward and into that hole.
Jim Hall: Mr. Wildey, who else looked at these holes, and is this the opinion of basically the Sequencing Group report that was placed in the docket?
Jim Wildey: It is the opinion of the Sequencing Group, and it is a factor that was signed off on by the entire Sequencing Group. But we discussed this with a large number of people and there were all kinds of people there who would bring various features to the Sequencing Group's attention and we tried to address every single one of these as they were brought forward and I think we did that quite successfully.
Jim Hall: Do you have rough guesstimate of how much time you spent up in Calverton looking at the metal and the structure of that particular aircraft?
Jim Wildey: I spent a total of 90 days on the accident investigation last time I counted. I will say that not all of that was part of the Sequencing Group but the vast majority of it was.
Jim Hall: And do you think that was an adequate amount of time for you to form your opinions?
Jim Wildey: Yes, I do.
Jim Hall: Member Hammerschmidt.
John Hammerschmidt: First of all I'd like to thank the staff for their very excellent and professional presentations this morning. A great job. And also for a good and comprehensive job on this report, as voluminous as it was to try to digest and work through for the past several weeks. As we've been talking about the procedural aspects of this investigation, it occurred to me that in many respects the way we approach this investigation in terms of the material failure analysis or the structural failure analysis from an in-flight break-up that ended up in the ocean is in many respects similar to the work we did on the space shuttle Challenger investigation where we started out with two-dimensional layouts of much of the wreckage and the fuel tanks of that space launch vehicle and then we completed a three-dimensional mock-up of the orbiter and came to conclusions in terms of break-up sequence as we're terming it in this report. So that struck me as somewhat analogous to the procedures that we employed in this investigation and when we're talking about structural failure analysis we're really talking about, essentially, accident investigation 101 in terms of witness marks and what hit what first and how material breaks apart and what that shows us, especially when we put under the scrutiny of an electron microscope.
The factual portion of these two discussion items is quite a few pages but I would like to select out just a few questions that I have, miscellaneous in nature, beginning at the front of the report and going back into the report. The first question is on page 124 and 125 where you make reference to some of the wreckage that was recovered from the green zone as we've termed out. At the bottom of page 124, we make reference to the tires of the aircraft. We indicate that the 16 main landing gear tires were recovered from the green zone and examined at the hangar in Calverton, We go on to describe what that examination revealed. Could staff please elaborate on what the evidence showed us from the tires that were uncovered.
Robert Swaim: The tires that were recovered were examined with the help of representatives from the tire company, I believe it was Goodyear, TWA, and the other parties helped so we did have a number of tire specialists with us. We also had some material folks with us. The bursts were consistent with impact-type damage or sharp object-type damage where we had fairly classic chevrons and so forth. Some of the tires had a light evidence of burning on the surface near structure that had a flow pattern of burning.
John Hammerschmidt: Did we find any evidence of a tire that had exploded in flight?
Robert Swaim: No sir. Tires in main landing gears that do explode, there's a lot of force in them and they leave a lot of damage. No we did not.
John Hammerschmidt: Thank you. Moving to the next question, also back in the factual section of the report. We begin a section on page 132 which we entitle "Brown Splatter Material on Air Conditioning Ducts." We go on to describe what was found in considerable detail. Would someone please describe what that refers to and what the significance or nonsignificance of that might be?
Jim Hall: Mr. Kolly, we've got a big room with a lot of people who want to hear, so please speak up and speak slowly.
Joseph Kolly: The brown splatter material that was found was an elastomeric???? material, and it was tested by the FBI, DERA (the Defense Evaluation Research Administration), ARTEC ??, and NASA.
Jim Hall: DERA?
Speaker: The Defense Evaluation Research Administration. It's a new one. They helped us throughout this investigation.
Jim Hall: I understand. We use a lot of abbreviations in government, and we've got a lot of people here that aren't in government that are interested and that we need to communicate with.
Joseph Kolly: The results indicated that this was consistent with a melting of a polyurethane foam that had covered the duct that was in that area.
John Hammerschmidt: Where I was going with that question was, we discovered these brown splatters and at first they raised question marks. And then we delved further into them, and we did an elaborate evaluation of them and determined that they really weren't that significant.
Bernard Loeb: There was an issue raised fairly early in the investigation by one or two of the investigators about what this brown splatter meant, this dark splatter. And there was at one point a suggestion that it meant that there may have been a fire that initiated outside the fuel tank - it's part of the insulation, the duct insulation - to melt the polyurethane and get it splattered onto the various members, including spanwise beam 3, and inside some of the ducts. The issue was raised, how could that have happened in the fuel tank explosion. And we've gone through that in great detail. There was also a report that there were fiber materials in the splatter, which we have identified as materials from the carpeting in the airplane. We went into other airplanes and found the same kind of fiber materials throughout some of the same locations and did an extensive analysis and determined that all of that was consistent with the break-up as we see it of the fuel tank and with the scenario we have given you.
John Hammerschmidt: Thank you. Because we're dealing with the section entitled On-Scene Accident Investigation and Recovery, I was going to ask about the nature of the recovered electrical components and wiring from the vicinity of the center wing tank.
Bernard Loeb: Bob Swaim is going to have a presentation that will talk about that, and we'll go into that in great detail at that time.
Jim Hall: Okay, thank you. You were referring to a section of the factual portion of the report entitled "Information Regarding Certain Primary Radar Targets Recorded by the Islip, New York Radar Site." The factual begins on page 155. And we also make reference to that issue, I believe, in the analysis on page 456. Since that hasn't been addressed yet, and it does fall within this discussion category of the break-up sequence, would someone wish to elaborate on what we learned in that area and what significance it might have to our understanding of this accident?
Charles Pereira: There were numerous primary radar returns recorded by six primary radars covering the accident. This particular section of the report covers the Islip primary radar den. There were several sequences of anomalous radar returns well away from the accident area that we went ahead and reviewed anyway to try to develop an explanation for them.
On this slide, in the lower left-hand corner, this is one of the sequences that you're looking at here. In the center there's a yellow dot that represents the last secondary return for TWA 800. The small white triangles throughout the plot represent primary radar returns and reflections of energy. It's not the airplane talking back to the radar; it's just a reflection; a bird or a building would create such a thing. The blue dots that are there represent secondary returns, the position of the other airplane talking back to a radar and the transponder. So on the lower left-hand corner there, you've got some primaries that appear and disappear and have randomly varying signal strengths. They only occur on the Islip radar, out of all the six primary radar systems looking at this area, Islip was the only one to show these and they only occurred on the 150 to 160-degree ?? And they occurred several times, both before and after the accident, always in the same area.
So we discussed these with FAA radar specialists and read various literature regarding false primary returns, and we also reviewed the Islip radar area for building structures that might cause such reflections. And we and the FAA unanimously came to the conclusion that if these were false primary radar returns then aircraft in other areas of Islip's airspace that were being reflected off some building structure and showing up in this area in a random fashion.
So this particular section of the report that you raised questions about, that's what we're discussing. If you have any detailed questions on that I'd be happy to answer them.
John Hammerschmidt: No, I was just hoping to get a brief explanation of that and that was just right. Thank you, Mr. Pereira. Continuing on with the report, on page 167, line 4, in the part of the report where we're talking about the break-up sequencing, we state that the timing of the wing tip and wing center section failure were based largely on witness statements and therefore are not precise to the second. Could staff elaborate on that sentence, that reference?
Bernard Loeb: Yes, the sentence is essentially what it says: We have no other basis for determining when the outer sections of the wing failed, other than the witnesses, and we got that information based on the description of the fireball and the developing progress of the fireball and the further eruptions that occurred in their descriptions. We coordinated that with certain other events that we did have in a fixed time, for example, the captain of the Eastwind flight who had seen this - he was about 20 miles away or so- he'd seen what he believed to be landing lights of an airplane approaching him coming out of JFK. In fact, he flicked his landing lights to indicate to the airplane that he was where he was and to give them a warning. He was the first one to report that there was an accident, and he reported that to air traffic control.
So we had the timing of that event, and he gave us some information that indicated when this thing developed and when the outer portions of the wings must have broken, because that was how fuel got out before the airplane fully came apart. Later on the left wing broke and then the right wing broke off from the remaining pieces of fuselage. Prior to that we had to have a source of fuel for the fire that was being seen and was reported by the captain of the Eastwind as this great explosion. And so that's how we timed the outer portions of the wings, and there was no precision to that; we were within a few seconds, but that's the best that we could do.
John Hammerschmidt: Thank you for that explanation. The reason I brought that up is because when you say in your report in witness statements, oftentimes someone thinks of people standing on the ground looking a great distance, but this was in fact the pilot of another airline.
Bernard Loeb: That's correct. And a pilot who had reported into air traffic control, so that we could actually time when that occurred.
John Hammerschmidt: Thank you. Proceeding on in the factual, about page 203, we have a table in which we describe the 747-100 wing center section, center wing tank component failure strengths - minimums and maximums for the different sections within this center wing tank - such as spanwise beam 3, spanwise beam 2, etc. And we have described also, in the presentation thus far, that we think that this in-flight break-up initiated with an overpressure event. In terms of this Table 3, we have data that's in PSI, pounds per square inch. Do we have any way of calculating what we think the pressure of the overpressure event was in this accident sequence?
Speaker: The next presentation will be Dr. Joseph Kolly, who will go into that end of it, in other words, what we believe the pressures that were developed would have been. If your question is more to the structural capacity of these members, then Jim Wildey could answer that for you now.
John Hammerschmidt: I'm jumping ahead on that a little bit. But speaking of these beams and spars in the center wing tank, Mr. Wildey indicated in his presentation that they were primarily designed that way for structural reasons. Were there any considerations given to their location having to do with protection against fuel ignition in the center wing tank or am I jumping ahead on that as well?
Jim Wildey: I don't think that the tank is designed to withstand the stresses generated by an explosion of the fuel/air vapor mixture. The loads, primarily of the internal components, are loads associated with sloshing of the fuel and things like that, which are relatively minor. So the structural strength is also necessary to carry the stiffness requirements and the reinforcement requirements for the upper and lower skin panels. I believe these are the major criteria that are used to design the sizes of these internal beams.
John Hammerschmidt: Well speaking of sloshing, was any consideration given in this design in reference to, say, sloshing to prevent that because sloshing might aerate some fuel to perhaps generate a greater fuel/air mixture than would otherwise be present?
Jim Wildey: The sloshing loads are mainly.... If you didn't have any internal beams, for example, as you stopped on the runway, the fuel in this large tank could force itself against the forward boundary member, so one of the things that the internal members do is that they meter the fuel, if you will, they slow it down so you don't get this large surge against any of the members as you're turning or decelerating, and that is a consideration in the design and the strength of these beams.
John Hammerschmidt: Right. Thank you. That's what I was trying to get to. Concerning some work that we reference in the section beginning on page 233, "A Study of Computer Model Calculations of Full-Scale Center Wing Tank Combustion"....
Jim Wildey: Again, Dr. Kolly's going to cover this in his next presentation.
John Hammerschmidt: In that case we'll just wait until then. As I say, those were excellent presentations and when you have great presentations like that it cuts down on the questioning. That's all I have.
Jim Hall: Very well. We will turn to Member Goglia
John Goglia: Thank you, Mr. Chairman. I just have a few questions and I guess I'll take them in sequence. Dr. Loeb, in your opening statement you mentioned the seats, the work that was done with the seats in the cabin interior. In this airplane accident investigation and the reconstruction effort, we did something that was quite unusual inasmuch as we put the entire interior of the airplane back together as best we could. I wonder if you would take a moment to explain just why we did it and what we gained from that effort.
Bernard Loeb: I'll try to do that. Early in the investigation, of course, there was a lot of issues raised about the possibility that there was some sort of a high-energy explosive detonation in the airplane caused by a bomb or a missile, a bomb had exploded or a missile warhead had exploded inside the airplane. For that reason, and other reasons, we attempted to reconstruct the seats and the interior of the airplane to see whether there was any evidence in the cabin area that would point to the location of an explosive device or to give us any information about whether there was in fact evidence of a high-energy explosion. So we gathered as many of the seats and also galley equipment that we could and they tried to reconstruct to the best of their ability. One of the difficulties is of course trying to determine where the seats go and there's numbering issues that make it very difficult, although a number of these seats did have numbers on them so it did make it possible for us to reconstruct essentially what would have been the cabin interior in terms of the seats. Our examination of that determined that there was, as I indicated, no area where locally the damage was a high degree of fragmentation and a high degree of thermal damage, so that's one of the major things we got out of the seat locations. Also, there was an examination forensically of the occupants to see if there was any evidence - the same kind of evidence - on the passengers. One of the difficulties there is that passengers don't always sit in their assigned seats so it's very hard to draw strong conclusions from that, but because we were able to get the seats and pretty much locate them what we found out was that the damage and in fact the burn patterns were very consistent with what we would expect from first of all the explosion in the center wing tank and second of all the water impact.
John Goglia: Thank you. Mr. Dickinson, I have a question that goes to the tagging. We've talked a lot initially here about the three zones, the red, the yellow, and the green zones, and the tagging of those parts. Someone told me once that there was a million pieces that were recovered. I don't know if that's an accurate number or an inaccurate number. It really doesn't matter. There were a considerable number of pieces found, which we labeled red, green, or yellow. Human beings being what they are, there were probably mistakes that were made in that. Are you comfortable in your own mind that we have factored in the possibility of those mistakes and that there's very little impact to the actual investigation if there were any mistakes?
Al Dickinson: Yes, I am comfortable. You have to realize that it was the first full recovery of an aircraft from 120 feet below the ocean surface that we had ever attempted and we had some situations where pieces that were recovered from certain areas had fallen off from various things as far as mis-tagging but we adjusted and we went back and looked into every piece and have fully identified as far as we can tell and we're fully satisfied that the tagging system is accurate.
John Goglia: I would like, if you wouldn't mind, for Dr. Meyer, since he was in charge of the tagging and the database project, to perhaps say a word or two about the tagging process.
Jim Hall: Well, in leading into that, let me just make an observation. We had participated with the supervisor of salvage I think twice before this particular accident, once on the recovery of an aircraft door in the Pacific, a cargo door, and the other was on the Bergen?? Air crash. There may have been other instances ... and the AeroPeru, and Valujet has assisted us in the Everglades. But this was the first time in this depth of water. Since that, of course, we have regrettably had the SwissAir accident, which is investigated by the Transportation Safety Board of Canada, as well as Alaska Air and EgyptAir. We have learned a lot and things have refined but Dr. Meyer, if you would please go into that answer to Member Goglia's question, but I think it's very important that people following this investigation are aware that this is the first time that an entire aircraft like this has been recovered and there have been attempts to document the recovery of all the various pieces of the aircraft. Doctor.
David Meyer: Mr. Chairman, early on in the investigation it was recognized that there was a need to track evidence both for purposes of criminal investigation and also for purposes of the accident investigation. It was very important to know where pieces were recovered to enable a number of studies that we were certain would follow up on the recovery process. The way this done is that as pieces were recovered at sea they were tagged with a color-coded tag, but that's not the only information we got about pieces. In addition to the color-coded tags that were attached directly - aluminum tags like these - paperwork was filled out and documented that took a separate path back to the hangar.
What occurred is that the pieces were transported back to the hangar with their tags on them, but the paperwork documenting where those pieces were recovered took a different path and were transported also back to the hangar. We set up a database staff to read each sheet of paper that came in - there were thousands and thousands of sheets of paper that documented the wreckage. On the sheets of paper we didn't just document whether it cam back from the red, yellow, or green zone, we documented the specific latitude and longitude from which the piece was recovered. We used those pieces of paper to validate every single piece that was tagged at the scene to determine whether or not the tag color was correct based on the latitude and the longitude.
We also had another built-in check that we were able to use. A lot of pieces were recovered by mobile dive teams, in other words, sonar operations in the first week or so of the search operation identified thousands of targets and those targets were dived on during the coming months in the recovery process. As each target was dived on, it was assigned to a mobile dive team. The mobile dive team went to the assigned latitude and longitude, the assigned location of the piece, recovered the piece, and wrote down taking a separate GPS (global positioning system) reading where they were as the pieces were recovered.
All of that information came back to our data center in the hangar. We worked through each of these pieces to determine if the pieces that were tagged at sea were tagged with the appropriate colors based on where the diving operation was assigned and where the dives were accomplished. We spent months reconciling that information and I am confident that we have a good product that documents the recovery positions of all the ship-tagged items.
John Goglia: Thank you.
Jim Hall: If I may interject one more time, I apologize. We also had video, did we not, of a lot of the underwater recovery?
David Meyer: That's a good point, Mr. Chairman. We had underwater video that was taken by the ROVs, the remotely operated vehicles, the submarines, and we also had, in addition to the sonar images, we had laser line scan images. It's sort of an underwater television technology. We had all of that information available to us as we checked those pieces. In fact I've seen some members of my team in the audience here today who spent literally hours accomplishing that work.
Jim Hall: And I want to ask, Dr. Meyer, and Mr. Dickinson, and I apologize in advance for having to ask this question, but do you know of anyone who intentionally mistagged a piece of wreckage so we wouldn't have the factual information in order to proceed with this investigation?
David Meyer: No sir.
Al Dickinson: No sir, I do not.
Jim Hall: Thank you.
John Goglia: I have a couple of questions for Mr. Wildey and I'm trying to put them in order. Mr. Wildey, you mentioned the water bottles. For the benefit of the folks that were not in the hangar and did not receive the in-depth briefing that you provided to several of us Board Members, which we greatly appreciated, would you just go into a little bit of detail and explain the significance of those bottles? What were the size? You mentioned the location, and in fact it's on the screen now. And why were they important to the investigation?
Jim Wildey: I don't have the weight, but they are very heavy. They are large water bottles about 2 feet in diameter and maybe 5 to 6 feet tall, and there are two of them and they are the drinking water that's carried in the airplane for the passengers to use. Their significance was that they provide a large inertial resistance to motion of the front spar and during the break-up sequence as spanwise beam 3 fractured, the releasing overpressure from the wing center section began to act on the aft side of the front spar. When we reconstructed the front spar we found out that the spar had come kind of bulged forward in two lobes, one on either side of the center, and our conclusion was that these water bottles acted to restrain the center of the beam of the front spar, and that these two lobes bulging forward on either side, were a sign of the pressure acting on the aft side of the front spar.
John Goglia: Thank you. Also, I wonder if you could put the section of the fuel tank up that shows the keel beam. Now I'm going to take a little liberty here and call the keel beam the backbone of the airplane for the benefit of folks here who are not aeronautical. The backbone of the airplane, in this case the keel beam, only extends to the rear of the forward cargo compartment. But in order to hang such a large structure, we still need the equivalent of a backbone to carry up to the front of the airplane - for example, to take the loads from the nose landing gear and just the weight of the rest of the airplane, which is pretty big in the front. To accomplish that, that backbone then changes form and it changes to a structural member that actually represents the floor of the cargo compartment.
In your description, you went over that a little bit lightly - the significance of that large piece of fuselage that failed very early in the sequence. I wonder if you would go back and try to explain for the benefit of others here just what the significance of that event is.
Jim Wildey: The keel beam broke approximately in the middle, underneath the wing center section. I don't think we have a good picture of that, but about halfway back through the tank is where it fractured. The forward end of the keel beam came out early on in the sequence, with the red zone pieces, and it was found in the red zone. The aft end of the beam remained with the rest of the structure and was found way down range in the green zone. So it's clear that the forward part of the keel beam came out early on.
Now what our group determined was that the piece created in the fuselage, which is connected strongly to the bottom of the keel beam, once it fractured around three sides of this piece of the fuselage structure, there was sufficient loads downward on this structure forward of the keel beam to physically pull it out from the bottom of the skin - the lower skin of this wing center section - break bolts that attach it to the wing center section, and then fracture that beam about halfway back. So it was part of the overall sequence and we did analyze, using stress analysis, how this could occur, and developed a rationale for the fracturing and release of the forward portion of the keel beam.
John Goglia: Would you move forward now to the portion underneath the cargo compartment floor?
Jim Wildey: That would be number 16, I would think.
John Goglia: I think many in this room would benefit from the significance of this forward area and what it means to the forward portion of the airplane.
Jim Wildey: The significance is as high you can get. If you lose the lower portion of the fuselage in this area, you have no capacity to take the bending loads from the nose section and at least one of the features that we saw after loss of the structure from window belt to window belt as a part of the initial event, then the nose simply started to fold down because there's no capacity for taking the bending of the nose down. And we saw this compression damage extend from the window belts up towards the top of the airplane. Once this hole is created across the bottom, the nose portion is going to come off.
John Goglia: Thank you. That wasn't clear in your initial presentation. Another piece of significant work that you and your team have accomplished that you went over rather lightly, I thought, was the rivet-to-rivet analysis that you did of the fracture. The rivet's facing is about 3/8 of an inch?
Jim Wildey: I believe it's about one inch.
John Goglia: So this jigsaw puzzle of fractures that are out there, your team analyzed inch by inch. That's a significant amount of work.
Jim Wildey: I would agree with that, yes sir.
John Goglia: I don't believe there was enough recognition of that given in the presentation. You didn't just take for granted anything as you went over the fracture.
And one last comment I've got was the speed of travel. You said that whole event took seconds. I recall that someone said to us early on that these fractures travel at about 6,000 feet per second, and since the airplane's only 225 feet in total length, 6,000 feet per second means that these fractures probably only took a second.
Jim Wildey: Yes, I think I can address that a little bit. There's kind of two phases of the early portion of the break-up. The earliest portion, the first part of it, would include a very, very rapid propagation of these early fractures in the fuselage, and that in fact occurs so rapidly that it gets out ahead of the escaping overpressure to a large degree. However, after these early fractures are created then things slow down a little bit and it takes several more seconds for the nose to come off as the fractures are tearing - not in a rapid manner but more of a tearing manner - across the top of the airplane. So the several seconds refers to the total separation of the nose, and certainly there would be something less than a second, I'm sure. I don't have the number for you, but it would be less than a second for the initial fractures of spanwise beam 3, the front spar, and these early fractures that we were looking at in the lower portion of the fuselage.
John Goglia: One last piece of this. And again it's for the benefit of those that may not understand this. I wonder if you could just explore briefly the shearing and tearing and the differences it meant to you as a metallurgist and to your team.
Jim Wildey: The fuselage contained - I can't put a number on it - a large amount of skin fractures, and one of our tasks was to look at all of these fractures and try to characterize them in terms of the sequence. There was an initial assessment that anything that fractured along the rivet line, for example, that would have been from an overpressure event. We quickly determined that that's not true. You can fracture along the rivet line from out-of-point stresses. For example, if the pieces on either side of the fracture are bending or deforming in any way next to each other, then we determine that there must have been other fractures somewhere else to allow these pieces to bend, relative to each other, before the fracture occurred.
That's distinctly different from these early fractures we saw, again maybe on slide 16, if we could put that back up there. These early fractures are distinctly different in that the pieces on either side of the breaks here pulled apart either in direct tension, with no deformation, or else in an unzippering effect. And that was the distinguishing characteristic that we used to distinguish these early fractures from the vast multitude of fractures throughout the red zone area and the rest of the airplane that occurred later because the pieces were moving relative to each other. I hope that answered your question.
John Goglia: I hope that it put some at ease that they now understand what we went through. One last question. I've had people ask me about Section 41 repairs - and I know you're familiar with that term. Section 41, for the benefit of others, is the forward section of the airplane, just after the main entrance door from the nose back. There have been some AD notes issued against this airplane - required inspections and repair from the FAA, that's what an AD note means. Did you find any evidence in your work to indicate that any of the repairs, or any of the issues in the Section 41 AD note was a factor in the break-up of this airplane?
Jim Wildey: We found that there were no issues related to that, we found no fatigue cracks in that area addressed by the airworthiness directives for the upper lobe, I believe it is. And also in that area, we looked at the Section 41, 42 joint, found no evidence of a preimpact with the water for that joint there at Section 41, 42.
John Goglia: Thank you, Mr. Chairman. No further questions.
Jim Hall: Member Black.
George Black: The wonderful thing about being this order in the sequence - there's not much left. Jim, would you talk a little about - a lot of this initial break-up came around the area where there was a pairing for the wing, was there not? That pairing is fiberglass, is it not?
Jim Wildey: It's a honeycomb and fiberglass. It's not designed for structure; it's just designed to smooth the transition from the wings to the fuselage, and things like that.
George Black: And that material, for the most part, was part of what the chairman was talking about earlier about floating material that was found early on, and we could not place it.
Jim Wildey: And also we did find a large portion of the right wing that was floating. That was, I believe, the largest structure.
George Black: I guess the point I'm trying to make is a lot of this pairing would have come off and been floating would have actually been red zone material because it goes around the area that trailed. In connection with that, could you talk a little bit about the effects that airflow would have had on this belly skin area as it was coming loose? In other words, there's still a slipstream of close to 400 knots there. Would you talk a little bit about how that would have helped unravel that area around that ultimately ran to the front section departing the airplane?
Jim Wildey: We talked about this a little bit before. The early fractures that I discussed happened so fast that the air stream flow doesn't really have time to really act on them before they're created in the present. After they're created, the piece from the lower portion of the fuselage is pushed downward by the pressure differential inside the airplane, and that piece then would get into the air stream. Again, though, this is happening very dynamically, and I believe that a lot of the fractures in even of the keel beam are happening probably before the air stream has a chance to really play a major role in the break-up.
George Black: The only party that dissented to some degree to our report, in the conclusions during the factuals, raised this issue about the area around, I believe it was, the number 3 left door. Could you talk a little about what they're talking about in their party's submission there? Or is that to be covered later?
Jim Wildey: I'm not sure what that issue is. Perhaps someone else can address that.
Bernard Loeb: Member Black, the truth of the matter is, I'm not quite certain what the IAM is trying to say in that submission regarding L3 door, but it appears that they're trying to indicate that there must have been some sort of an event in that vicinity that led to a structural failure initially that then led to the explosion in the center wing tank. What I can tell you, and I think Jim Wildey can address further, is that we looked at those areas very closely, saw no evidence, none whatsoever, that there was