Ten years ago this month our aviation community suffered its second major hull loss in two months. On the heels of the ValuJet Douglas DC-9 crash in Florida, a 747-100 operating as TWA Flight 800 from New York to Paris entered a rapid descent after takeoff from Kennedy Airport and crashed into the Atlantic Ocean more than 10 miles south of Long Island on July 17, 1996. At more than $50 million, this would turn out to be the most expensive accident investigation in U.S. history.
The aircraft debris field was spread over more than five miles of ocean at a depth of about 120 feet. A debris field of this size would have been a challenge on land, but its being under 120 feet of water added a level of complexity that was simply staggering.
If that weren’t enough, we also had to face the very real possibility that the event was a deliberate act of terrorism. The government was concerned that attacks against commercial aircraft in other parts of the world had spread to the U.S. We had similar concerns during the initial response to the ValuJet crash, but a few months into that investigation the facts pointed more to an accident, not terrorism.
When the TWA disaster happened we had not yet determined whether the ValuJet crash was a deliberate act or, as we later labeled it, an accident. As a result, the response to the TWA 800 crash off Long Island had a huge police involvement because it was believed a deliberate act had brought down the airplane. This caused difficulties for both the police/FBI and the NTSB. Was this a crime scene or an accident site? The answer to that question would determine who would lead the investigation.
The FBI presence on Long Island, in terms of manpower, exceeded the total number of NTSB personnel nationwide, so they took control. It would be many months before
the FBI would pull back from the position that this was a deliberate act. The NTSB was able to secure an agreement that a parallel investigation would serve both agencies’ needs without compromising the interest of either. Although the parallel investigations added considerable complexity to the process it did work out mostly to everyone’s satisfaction.
The normal response to such events initially is to focus on the search for any survivors, and that is what happened. However, the NTSB and the FAA both started securing the recordings of all radio communications between the aircraft and ATC, all the radar data from the FAA radar centers and any data that was available from any other sources. While the rescue and then recovery efforts were in progress, we assembled some of our nation’s best and brightest radar experts to review what we had collected. This was a time-consuming and a time-sensitive task.
Think of what is required to synchronize the radar data from several locations so that at the exact same time you can compare what is being displayed. Later, when the missile theories came to the forefront, this would prove to be time well spent. One of the challenges that these experts needed to resolve was the lower resolution from an aircraft after loss of electrical power knocked out the transponder.
Later in the investigation, researchers carried out tests to determine if these radars could track a missile that was fired at an aircraft in flight. At the point from which it began its fatal descent into the water, the 747 was flying higher than the highest altitude for a portable missile to be effective, and larger missiles would have been observable.
Mapping the Debris Field
We learned just how difficult this investigation was going to be after finding early on that the debris field was much larger than what we normally encounter. Recovering the victims’ remains had become a priority; recovery of the aircraft took second place. When I think back on the search for human remains, I realize what a tremendous feat the U.S. Navy accomplished in the recovery of all 230 victims. It never received appropriate accolades for what it accomplished.
The Navy also mapped the debris field on the ocean floor and videotaped the locations. As the aircraft was recovered it became clearer that it had broken up in flight, which only added to the possibility of terrorism. In fact, the “reading” of a debris field can be arduous and misleading, and trying to draw conclusions from one that is beneath 120 feet of water presented yet another layer of difficulty for both the NTSB and the FBI. Here again there was enough evidence to indicate the possibility of a terrorist act.
While the NTSB and FBI investigators were hard at work, the press was having a field day with front-page stories based on little fact and a considerable amount of speculation. Comments from people who knew small slivers of fact were expanded by some reporters into “major findings.” Soon the inaccurate statements were feeding off each other. This still affects us today, as many of the conspiracy theories have their origins in those inaccurate news reports.
As the Navy brought pieces of the aircraft to the surface each was tagged with the location where it was found and inventoried and then tightly controlled. The possibility remained that this was a crime, and the courts require a continuous unbroken chain of custody for all evidence.
Soon there was a continuous flow of aircraft parts to the former aircraft assembly plant we were using to examine these parts in great detail since the question of a crime or an accident was still unresolved. During an accident investigation one of the things investigators do in evaluating the debris field is to go back in the direction the aircraft came from and see what separated first.
We did that after the crash of TWA 800, and what we discovered only added to the possibility that the event was the product
of a deliberate act. We found that the area just forward of the wing for 360 degrees around the fuselage was among the first pieces to leave the aircraft.
No Evidence of Explosives
Many believed that an explosive device was the only explanation for that sequence of events. Since this area contains the forward cargo compartment, investigators began to reconstruct this section of the aircraft. We also started to reassemble the seats and galley areas of the cabin, looking for telltale signs of an explosive device. Over time this reconstruction effort grew, and in the end we had pieced together approximately 93 feet of the aircraft, inside and outside, including placing the seats and galleys back where they came from.
One of the little-known facts about TWA 800 is that each seat was numbered on the armrest rather than (the current practice) on the overhead storage bins. As a result, we could study each seat that was positioned above the cargo compartment for any signs of damage that originated from below.
During the investigation, no damage unique to explosive devices was found. Examination for injuries caused by explosives was part of the passenger autopsies, and there was no evidence of such injuries. The aircraft interior sidewall, lavatory and galleys were also closely examined for any signs of damage from an explosive device. None was found.
It was during this part of the investigation that a member of the team told the press that rocket-fuel residue was found on a passenger seat. Further testing revealed that what was found was a chemical element inherent in the manufacture of the glue used on the seats. Since all the testing required to determine the origin of the chemical residue took some time, the press ran more headlines based on weak facts.
In the account so far, weeks and weeks of effort by the investigation teams have been compressed into a brief summary, and it needs to be said that these men and women worked 16-plus hours a day for many months without a day off. My hat is off to all of them.
After the cockpit voice and flight data recorders had been recovered and examined, we realized that all electrical power had failed instantaneously, so we decided to examine the wire in the area of the forward cargo compartment. All the wire recovered from the accident site was assembled in one area, and the arduous task of identifying each and every piece began.
I’m told that this model of 747 has approximately 140 miles of wire and, having seen the pile laid out in the facility, I believe it. Over time, the small team assigned to this task found and identified the wires we were looking for. Subsequent examination revealed that there was no damage caused by an explosive device. This search also provided insight into the condition of the wiring in much of the aircraft and raised several major concerns.
Focus on the Fuel Tank
The beginning of the debris field also had components from the air-conditioning system. Also recovered in this area was a large I-beam that can be described as the backbone of the aircraft. This extremely strong piece of aircraft structure is located directly under the fuel tank.
As time went by, more small pieces recovered from this area were determined to have come from the interior of the fuel tank, raising more questions about what could have happened to expel these pieces from the aircraft so early in the accident sequence.
All these seemingly unrelated findings were coming together and leading us toward some early conclusions. We would now be able to focus additional resources on these areas.
One major avenue of investigation not normally accomplished on such a large scale was determining the sequence of the aircraft disintegration. Some of the best minds from several specialties were assembled to provide a detailed map of how the aircraft broke apart. What these people learned about the forces that shattered the aircraft proved invaluable to the investigation.
Their examination of the fuselage skin helped clarify, for many, how this accident happened. The skin of the reassembled aircraft clearly resembles a giant jigsaw puzzle. Metallurgists examined many of those pieces to determine the force that was applied to tear the metal apart. The signature that such destructive forces leave in the metal is unmistakable.
As an aid to those reassembling the aircraft, the metallurgists placed small arrows pointing to the origin of the force. Once the pieces had been reassembled, the arrows pointed to the center fuel tank. This alone was not enough to declare the accident solved, but it was certainly strong evidence as to the energy source that destroyed the structural integrity of the aircraft.
Physical evidence was leading us increasingly to the center fuel tank, but we still needed more. Although there had been other fuel tank explosions they were rare, and we still had not located an ignition source. More work would be required to determine how much force the vapor could generate inside an almost empty fuel tank.
We equipped a 747 with test equipment and placed it on the ramp at JFK on a day similar to the hot July day the accident aircraft departed. We discovered that under those conditions the fuel tank became rich with vapors, needing only an ignition source to cause a disaster. We also conducted scale-model testing of fuel tanks to determine how they would fail under conditions similar to those we believed prevailed on the accident aircraft. Considerable testing produced results closely similar to the physical evidence the accident aircraft had revealed.
This was another powerful clue. However, we did not stop with scale-model testing. We accepted the opportunity to study a 747 fuel tank on an aircraft that was being destroyed in Bruntingthorpe, England. The testing revealed a breakup similar to what we had documented in New York. We studied the fuel used in modern jet aircraft, the physical properties, density and flammability.
Not all jet fuel is the same, and the differences can be significant. A lot of work went into trying to determine exactly what fuel was loaded into the center fuel tank
of this aircraft when it passed through Athens, Greece, en route to New York. We reviewed all the previous accidents in which jet fuel was a causal factor, including the Avianca 707 fuel-exhaustion accident on New York’s Long Island some years earlier. We also reviewed the FAA research into low-flammability fuels.
Finding the Source of Ignition
The search for an ignition source continued in earnest. Since the air-conditioning system was located under the center fuel tank and it was found among the
first pieces of debris, it was an early suspect. All the recovered components were reassembled and studied in an attempt to prove or disprove the involvement of the air-conditioning system as a source of ignition. Investigators ultimately exonerated it.
The team then examined the engine bleed-air system, which provides extremely hot air under high pressure, but ruled that out too. They also dismissed the pneumatic system after extensive review.
Investigators then scrutinized the electrical system. Not only did many people believe it was the likely source of ignition, but the previously mentioned wiring work revealed some of the wiring to be in poor condition. The NTSB actually devoted a team to nothing but wiring, and this group did an outstanding job of identifying several problems that resulted in an FAA working group that is still working on these weaknesses today.
The wiring group found in storage in Arizona a 747 that had been manufactured at the same time as the accident aircraft. We were able to gain access to the wiring from the wing root to the cockpit, and what we found was of real concern. The cracked and brittle insulation on some wires (not just one or two but a significant number) had vibrated loose, exposing bare wire. We also found evidence of considerable arcing, which could have led to a fire.
Modern aircraft use both AC and DC electrical systems as each has advantages depending on their use. In the bundles running from the wing to the cockpit, we found that the insulation had deteriorated to the point that mixed voltage wires were bared and touching. The intrusion of 115 volts into a low-voltage system would cause major problems.
We found that the fuel-quantity indicator wires were in this bundle, along with the fuel-flow indicator wiring, and in so doing we had discovered a potential avenue for electrical energy with enough power to ignite fuel to enter the fuel tank. Low voltage was a cornerstone of protection for the fuel tanks. On the Arizona aircraft we also discovered potential problems with the wiring inside the tank that could allow high voltage to arc inside the fuel tank.
However, most people were confident that the wiring inside the tanks would be sound since maintenance programs would have revealed any problems before they could cause an accident.
Was this promising theory suddenly a dead end? No. A couple of sharp-eyed mechanics working inside a 737’s center fuel tank (built to the same standards as the 747’s) noticed that holes had been burned through a conduit carrying wiring through the inside of the tank. The wiring inside the conduit had burned through the tubing, and it was great luck that this hadn’t ignited a disaster.
Many more industry leaders came to believe that conditions could be ripe on other in-service aircraft for a repeat of the TWA accident. It was fortunate in the extreme that these mechanics noticed the holes, since they were not performing an inspection in that area. Their diligence resulted in inspections of the entire 737 fleet and renewed interest in the weaknesses of aging wiring.
After several years of investigation, findings and NTSB recommendations, the FAA took some action by requiring any aircraft certified in the future to render inert the volume of its tanks not occupied by liquid fuel. However, the airlines have objected vigorously to the cost and complexity of retrofitting existing aircraft with fuel-tank inerting systems.
Almost everybody who was involved in or close to the investigation believes we determined the cause and developed solutions to prevent a repeat of the accident. However, there are some who still believe the conspiracy theories that have their origins in the news or in the hastily written book that were written early in the investigation process.
As a member of the NTSB at the time, AIN columnist John Goglia spent untold hours at the scene of TWA 800.