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The TWA Flight 800 hearings wrapped up. Tom Bearden gives a background report, followed by discussion with National Transportation Safety Board Chairman, Jim Hall.

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TOM BEARDEN: Why the plane went down remains a mystery. Despite the longest and most expensive accident investigation in American history, no one can say what caused the center wing tank of that Boeing 747 to explode, killing 230 people. From the beginning the FBI and the NTSB looked at three different causes: a missile, a bomb, or a mechanical fault. After a year and a half of intensive examination of the record, both agencies ruled out a criminal act.

RICHARD BOTT, Naval Air Warfare Center: There are no places on that aircraft, no places of missing structure that are large enough to contain enough damage that had not been recovered.

TOM BEARDEN: Early on, NTSB investigators focused on the center wing tank. It had long been known that explosive vapors form in all aircraft fuel tanks as they empty. The liquid fuel gives off volatile compounds that mix with the air in the empty spaces. But it takes a spark to set them off, and the whole history of aircraft design of fuel tanks centered on eliminating any ignition sources. But something set off the fuel-air mixture, and much of the testimony this week centered on the 747's electrical system. Wiring recovered from TWA 800 was found to have damaged insulation, and the board wondered if that might have somehow led to the introduction of a spark inside the fuel tank. A potential route could have been through the fuel probes, aluminum cylinders that use a small amount of electricity to measure fuel quantity, too small to have set off the vapors.

LOU TAYLOR, Honeywell Engineer: The normal operating voltage for tank units in the center wing tank we operate these five volts. You have no idea if this is on or off if you're holding the wires, so this is an extremely low energy system.

TOM BEARDEN: But investigators have wondered if an aging wiring harness--the plane was 25 years old--could have accidentally introduced much more electricity into the tank. The board also believes heat may have played a role. They noted that Flight 800 sat at the gate for several hours with its air conditioning system running, a system that is located under the tank. That heated the small quantity of fuel in the tank to fairly high temperatures, and it takes less energy to ignite warmer fuel. The board leased a 747 and duplicated Flight 800's take-off and climb to the explosion altitude to measure the vapor in the tank and conducted explosion tests with a scale model of the tank. That led to a series of recommendations that the industry take steps to lessen the flammability of the tanks. Several measures are being examined, including the use of another type of fuel called JP-5, which is less volatile than Jet-A, the standard fuel today.

JIM HALL: Does it cost more at the pump, Mr. McSweeney?

THOMAS McSWEENEY, Federal Aviation Administration: The difference between JP-5 and Jet--JP-8--JP 8 is equivalent to Jet-A--is two pennies. What is that cost likely to be if it actually replaced all of the millions and billions of gallons of Jet A that we use today? The price is not trivial, but it's also is not enormous, and we just--it's just something we have to look at.

TOM BEARDEN: The board also wants the industry to look at several systems used in military aircraft to eliminate vapors, such as a foam product that fills the empty space. Another system is used on the C-17 transport. Onboard equipment extracts non-flammable nitrogen from the air, which is then pumped into the tanks, displacing oxygen and preventing ignition. The industry is also concerned about the weight of inerting systems, which weigh as much as a ton. That would reduce the range and capacity of aircraft. There are also concerns about whether such systems would themselves be a safety hazard. Michael Rioux is senior vice president for operations and safety at the Air Transport Association.

MICHAEL RIOUX, Air Transport Association: If you install a system of that type, what new problems does it create from a system safety standpoint? For example, gaseous nitrogen systems, if you had a reserve tank or storage tank, what would happen in the event of leakage into the cabin or the cockpit? As we know, nitrogen uses a suffocating agent, so to speak, and I wouldn't feel too comfortable and nor would any passenger feel comfortable having nitrogen leak into the cabin, or even into a cargo compartment, where we have live animals that are being transported for passengers.

TOM BEARDEN: Potentially fatal.

MICHAEL RIOUX: Potentially fatal, absolutely.

TOM BEARDEN: But as the hearings concluded this afternoon, FAA officials and manufacturers promised they would examine all of the NTSB's recommendations with an open mind.

IVOR THOMAS, Boeing Corporation: What we really have is an accident where we may not know the cause, but it has forced us--everybody in the industry to sit back and really evaluate all our fundamental premises for designing airplanes. And in the long run, even without knowing the cause of TWA 800, the end result would be much safer airplanes.

JIM LEHRER: Phil Ponce has more.

PHIL PONCE: Now, to the man who ran the hearings, National Transportation Safety Board Chairman Jim Hall. Welcome, Mr. Hall. First of all, Mr. Hall, what do you think the hearing accomplished?

JIM HALL, Chairman, NTSB: Well, I think it was very significant. It--I think we've accomplished a change in attitude in both the industry and the FAA toward the problem of dealing with the explosive vapors that are in a tank. We're going to see, I think, as a result of this hear, a lot of advances made in aviation safety that hopefully will make things safer in the future.

PHIL PONCE: Before we get into those specific kinds of steps, what was the intent of the hearing? How much of it, for example, was geared to the public to let them know how much word had gone on so far?

JIM HALL: Well, this is the 121st public hearing the National Transportation Safety Board has had in our 30-year history of doing major aviation accidents. The hearings are really an exercise in public accountability. It's an opportunity for the board and for all of those who have been involved with the investigation to spread that on the public record, all of the information that's been gathered.

PHIL PONCE: So from your standpoint, no new information came out, but you wanted this information to get out to the public, is that it?

JIM HALL: Well, it's a step in our investigative process, and it was extremely important in this particular investigation because, as you know, there was a parallel criminal investigation going on. And a lot of the information that we had we did not feel--we're not in a position to totally disseminate to the public until the criminal investigation had been resolved.

PHIL PONCE: So how further along is the investigation now than it was--how much more have you learned, for example, about 747's that you didn't know before the accident?

JIM HALL: Well, we've learned a great deal about the flammability of Jet A fuel, the effect that temperature can have where just a small decrease in temperature can have a great impact on the explosiveness of those vapors. We've learned a lot more about what is happening inside these aging 747 aircraft in regard to the systems of the aircraft in regard to the systems of the aircraft, things that I hope will get closer attention by both Boeing and the FAA, so a great deal has been learned and significantly as well as a result of the TWA hearing.

PHIL PONCE: Have you personally concluded that the design of the fuel tank is inherently flawed?

JIM HALL: No. We have concluded that there are explosive vapors in the tank. The philosophy of the FAA and the industry had been to remove the ignition sources. We have found from the Madrid accident, the Avianca accident, the Philippines accident, and the TWA 800 accident that that philosophy does not work every time, and although fuel-air accidents are extremely rare, we have got to take steps to remove the explosive vapors or eliminate or reduce the explosive vapors so we won't have an accident like this happening again.

PHIL PONCE: So, just to make sure I understand it, the first step was to make sure that nothing ignited; that was the original sort of guiding philosophy. Now, you're saying that the emphasis should also be on keeping the vapors down, is that right?

JIM HALL: That's correct. And we'll be moving on two fronts, a two-track approach, first to clearly look at the ignition sources. That's what the tank inspections that are going to be called for by the FAA are going to require. We're going to be looking at new technology in that area, is it possible to take all the electrical systems out of the tank--there's new technology in that area--while at the same time looking at how we deal with the explosive vapors and whether that can be dealt with by changing the fuel. As you know, the Navy uses another type of fuel because they do carrier aircraft, which is much less explosive than the fuel on commercial aircraft. So all of these areas are things that we're trying to advance our knowledge of and I think are extremely important because if you look at the increase in air travel that's going on in our country and in the world and the age of our fleet, it's extremely important that these things be done if we're going to keep the excellent safety record we have in the future.

PHIL PONCE: Speaking of the aging fleet, this plane was 25 years old. These planes are designed to--were not designed really beyond the life span beyond 20 years, and yet of the thousand 747's or so that are still out there, about two hundred and forty of them are older than twenty years. Should the public be worried about the age?

JIM HALL: Well, as they explained at the public hearing, they had--Boeing started out with an original economic life of these planes. Once they started going past that economic life there were changes in terms of the regulations and in terms of the Boeing service bulletins and requirements to ensure the safety of these planes in the future. Now, a lot of that work has specifically been looking at structure. If you remember the Aloha accident in Hawaii and looking at the integrity of the structure on aging aircraft, this hearing also focused and this investigation is focusing on those systems and should we be doing more and looking at the systems of aging aircraft.

PHIL PONCE: For want of a better term during the hearings it seems like at times you would almost take on a prosecutorial attitude towards the FAA and towards Boeing. Were you trying to sort of light a fire under them to do more?

JIM HALL: Well, the board, of course, has a responsibility to be the eyes and ears of the American people at accident sites, and that is a difficult and a challenging responsibility, and then work with the parties to the accident to come up with recommendations to prevent an accident from happening again. From time to time if we feel that things are not moving as quickly as they should, which I felt very strong about on ValuJet and the TWA 800 accident, I think it's our responsibility to bring that to the attention of Congress and to the American people.

PHIL PONCE: And, yet, if you're not exactly sure what caused the ignition, how does one know how to fix the problem?

JIM HALL: We know the center fuel tank exploded. We know that there are explosive vapors. We've learned a great deal more about the fuel, about the vapors. What we're trying to do is what anyone would want to do. What are the prudent steps that should be taken when you don't know exactly what happened? You try to examine everything around that event and try to preclude something like that from happening again. There are safety issues that the board comes up with in all of our investigations that may be not directly related to the probable cause but are things that we find in the course of our investigations that are significant to transportation safety, and we also move on that front as well.

PHIL PONCE: For the record--and this has been brought up many times--but are you completely positive that a bomb--that neither a bomb nor a missile were involved in this?

JIM HALL: I'm completely positive, because, No. 1, I have tremendous confidence in my investigators and the integrity of my investigators. I have some of the best people in the world. They've been up and down that wreckage, as I said, over it with a magnifying glass. They, the Bureau of Alcohol & Tobacco Firearms, the FBI, and independent people, have been all over that wreckage. There's no evidence of a bomb or a missile. And secondly, I have a great deal of respect for the Federal Bureau of Investigation and the integrity of Mr. Freeh and Mr. Kallstrom and all the individuals that worked on this investigation. If they found anything wrong, if they thought there was a criminal act, they'd tell the American people.

PHIL PONCE: In the meantime, there's no definitive cause for the crash. Is it safe to get on a 747?

JIM HALL: I think you have to look at the safety record of the 747 fleet, which is excellent, and you have to realize, which I hope these hearings have done, that the industry and the government regulators are moving to try to address any possibility that presently has come to our attention during this investigation that will preclude an accident from happening like this again.

PHIL PONCE: And very quickly, do you still get on 747's?

JIM HALL: Well, I'm going to go out and get on a plane tonight to go home. I doubt if it's going to Chattanooga, so it's not a 747, but I'll be going on 747's to the West Coast probably later this month.

PHIL PONCE: Mr. Hall, thank you very much.

JIM HALL: Thank you, Phil.

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