[Criminal Number 18F]

When the cockpit panel was recovered from the water, it was noted that the center tank fuel pump switches were off. I still fail to understand how a center tank pump can start an explosion when there is no electricity to the pump.

Good question, and the best theory (there's no solid proof) is that because of the decayed mylar insulation on the wiring, higher voltages from elsewhere in the plane's circuitry jumped to the pump wiring or (more likely) the fuel level sender unit wiring.

But the exact cause of ignition remains a mystery. There are several possibilities, but none of them is a solid lock. The official investigation admits this.

d.o.l.

Criminal Number 18F

[sinkspur]

Thanks for your calm, rational, and reasonable approach to the cause of TWA 800.

Some folks around here will simply not accept that some occurrences are accidents, especially when there's a convenient political demon to blame.

[Criminal Number 18F]

I wrote to aviator:

exact cause of ignition remains a mystery

Aviator probably knows this, but to recap on how we keep planes full of potentially explosive stuff from exploding all the time:

To have an explosion in a jet-fuel tank you need to have several things:

1. Fuel

2. air

3. an air space into which the fuel can evaporate forming a vapor. This air space is called the ullage

4. In the exact proportion that is inflammable, called a stoichimetric mixture

5. and the right temperature to encourage this evaporation

6. and the right ambient pressure

   ... and, finally, the granddaddy of them all:

7. a source of ignition.

Before TWA 800 designers concentrated mostly on eliminating possible sources of ignition. Since, operational considerations include not having fuel tanks contain an inflammable mixture in the ullage, to give belt-and-suspenders safety.

A third level of safety will be added soon by inerting, by putting inert gas into the ullage so that the fuel can't evaporate and form inflammable vapor.

Hope this helps. The explosion thing is kind of counterintuitive (if it happened once, why doesn't it happen all the time? people ask). The answer is, too many odd details need to fall into place, which is why it's happened only four or five times in millions of flight hours.

d.o.l.

Criminal Number 18F