As the Wrench Turns: Reconstructing TWA 800, Lessons Learned from John Goglia

In the end, more than one million pieces of the destroyed Boeing 747-131 that took off from JFK the night of July 17, 1996 as TWA 800 were collected and painstakingly pieced together. While some panels and light-weight structures floated on the waters of the Atlantic Ocean off Long Island, most of the aircraft pieces were collected from the ocean floor, at depths of 100 to 120 feet. More than eight miles from shore, the debris field was contained within a rectangle approximately 4 miles long and 3.5 miles wide. 
US Navy salvage teams spent months collecting pieces of the wreckage from the sandy bottom. In the limited visibility, large pieces like the Pratt & Whitney JT9 engines were relatively easy to spot but hundreds of thousands of other fragments – some smaller than the palm of your hand – were buried under several inches of sand. Fishing vessels – scallop trawlers - were hired to drag the ocean floor for these smaller pieces.
Salvaged pieces were brought to a large, unused hangar at a former military base in Calverton, New York. Each piece was numbered, inspected in detail and catalogued.   The larger pieces were laid out on the floor in their approximate location on the aircraft; thousands upon thousands of smaller pieces were piled in huge containers for later sorting.  Now, the largest aircraft reconstruction project to ever take place was about to begin.
At this point, some of you may be thinking, how?   How were all those thousands and thousands of pieces put together? Many of us can’t get passed jigsaw puzzles with a thousand pieces. A million fragment-puzzle seems impossible. Still others are probably wondering, why? Why put all this effort into a reconstruction? 
The why in this case was easy. There was no other way to figure out what had occurred. Unfortunately, even after the flight data recorder and cockpit voice recorder – the so-called black boxes – had been examined by NTSB experts, there was no obvious cause for the break up of the aircraft, barely twelve minutes after departure. For accident investigators, determining the cause of an accident is often the only way to prevent future accidents. And with more than two thousand 747s carrying millions of passengers around the globe, preventing a future accident was critical.
While the FBI pushed its theory that an explosive devise in the forward cargo compartment had caused the break-up of the aircraft, NTSB investigators were not so sure. Professional opinions on what could have caused the accident varied widely. A detailed reconstruction seemed the only way to piece together the clues to what occurred.
The how of the reconstruction was much more difficult. Boeing provided “life-size” drawings of the aircraft and TWA mechanics meticulously matched the pieces to the drawings, checking rivet patterns, material thickness, color and so on. It took approximately twenty mechanics, working grueling 12 and 16 hour days for more than a year to piece together almost 95% of the aircraft. But their efforts paid off.
In the end, reconstruction made a big difference in the determination of probable cause. The explosive device theory was disproved; there was no physical evidence that a bomb had torn through the aircraft. At the same time, reconstruction revealed important clues to what had occurred: metal inside the center fuel tank was deformed and distorted in a way that was inconsistent with impact damage. This led investigators to believe that an explosion had occurred in the center fuel tank. 
After extensive further testing and at a cost of approximately 50 million dollars the NTSB determined that the probable cause of the accident was an explosion of the center fuel tank resulting from ignition of the flammable fuel vapor in the tank. The source of the ignition could not be determined with certainty but was most likely caused by a short circuit allowing excessive voltage to enter the tank. 
Moral of the Story: Determination of probable cause is the Holy Grail of accident investigation. Reconstruction of TWA 800 shows how far the NTSB will go to determine what caused an accident with the goal of preventing future ones.