The NTSB investigation ended with the adoption of their final report on August 23, 2000. In it they concluded that the probable cause of the accident was “an explosion of the center wing fuel tank (CWT), resulting from ignition of the flammable fuel/air mixture in the tank. The source of ignition energy for the explosion could not be determined with certainty, but, of the sources evaluated by the investigation, the most likely was a short circuit outside of the CWT that allowed excessive voltage to enter it through electrical wiring associated with the fuel quantity indication system.”
It seems the NTSB and Boeing dismissed electrostatic discharge (ESD) as probable cause and, instead, latched onto a short circuit. In so doing they created a highly improbable scenario. Aircraft systems utilize low voltages ranging from 24 VDC to 30 VDC. By what means this range can transform into an “excessive voltage” without auto-inductive means in the indication system is beyond me. What am I missing?
Probable cause points to unruly, electrostatic energy. Air conditioning (A/C) units had been operating at full capacity while the aircraft sat on the tarmac for six hours in a hot July sun, thus lowering temperatures internal to the aircraft and raising ESD levels because of it. The units, which are adjacent to the CWT, had vaporized residual fuel within the tank through heat transfer. A bomb had been created waiting to explode. The fuse, it can be said, was the energy traversing the electrical wiring from the cockpit of the 747 to the fuel level sensor. The short-circuit notion seems to have been something pulled out of thin air.
The pilot had made an altitude change to 15,000 feet, as instructed by the air controller. TWA 800 had likely met its fate upon reaching that altitude, but what was the cause? Most likely it was ESD from pilot, or co-pilot, to gauges and switches on the console or display panel. Electrostatic voltage above several thousand volts had produced a `rogue spark’ that fused its way to the fuel sensor in the CWT and caused the explosion. Supportive of that was the pilot who noticed that the fuel gauge to Engine 4 was behaving erratically. It would be surprising if the pilot didn’t tap the gauge, as humans are prone to do, and in the process sparked the panel. A diverging spark would most certainly find the path of least resistance to discharge the energy. It’s anyone’s guess where that path might be and how many discharges had occurred in flights before. It’s frightening.