I saw a report on CNN a couple of weeks ago on TWA 800 and was surprised at how little technical information was presented in support of the investigators findings. The investigator had little to no electrical experience from what i could tell and came upon the conclusion that a spark ocurred in the auxiliary fuel tank.
They said that high voltage lines powering the lights run close to the low voltage fuel guage wires and because wires on a plane of this age have been known to crack they could have shorted together.
A couple of questions come to mind.
First, if these wires did short, why would a spark occur at the guage in the tank? Sparks usually occur where the short is.
They never attempted to explain schematically or otherwise any mechanism to explain their theory.
Secondly, what data gets recorded in the black box? They said all data looked normal. Does the fuel level of the auxiliary tank get recorded? If so, and a high voltage wire came in contact with the fuel guage wire, wouldn't the fuel level reading have jumped just before the spark?
I haven't had time to do much reasearch on the discussions contained in this website do forgive me if these questions have been covered before.
I worked on 747's for about 10 years at NWA, until they outsourced our jobs and forced us to strike in 2005.(but that's another story) After TWA800, we had to check all the fuel pumps and fuel quantity wiring harnesses in the fuel tanks. We didn't really find anything out of the ordinary, as far as I can remember. We had to make sure the pumps were electrically bonded within a few milliohms to the structure, alot of overkill maintenance as far I as am concerned.
The fuel quantity probes are lightweight metal tubes inside one another, which creates a capacitor. The fuel and air are the dialectric, different ratios of each determine the capacitance. The fuel processing unit calculates the amount of fuel in the tank on new digital systems, in old analog systems each guage in the cockpit calculated the fuel quanity. There are dozens of probes located in all the tanks. The center tank probably has 12 probes.
There are access covers to all the fuel tanks, the center tank is big enough for a 6 foot person to stand in it. I changed many harnesses and probes as part of normal maintenance. The wires get degraded in the tanks and give erronous readings. The amount of voltage going to the probes is really small, since they use a sine wave with capacitors.
The idea that wires shorted and caused the explosion is preposterous. The gap between the probe tubes is about 1/4 inch. I doubt a 120 volt short would be able to jump the gap, think of a spark plug, it takes many thousand volts for a spark to jump .032". I found quite a few short circuits on different aircraft, the only thing that happens is the circuit breaker pops, no spectacular sparks or explosions. I've never seen a wire short to another wire, it is always from a wire to the structure.
The "black box" (the flight recorder that is actually orange so it can be found easily) doesn't record fuel levels. It only records a limited amount of critical data like speed, attitude, flight control position, etc. The pilots monitor fuel quantity VERY closely.
TWA800 has been one of the best coverups in history. Aviation is a mystery to most people, including the journalists who keep us informed (or disinformed). Many if not most pilots and mechanics are convinced it wasn't a sponanteous explosion.
>>>>Original post: I saw a report on CNN a couple of weeks ago on TWA 800 and was surprised at how little technical information was presented in support of the investigators findings. The investigator had little to no electrical experience from what i could tell and came upon the conclusion that a spark ocurred in the auxiliary fuel tank.
They said that high voltage lines powering the lights run close to the low voltage fuel guage wires and because wires on a plane of this age have been known to crack they could have shorted together.
A couple of questions come to mind.
First, if these wires did short, why would a spark occur at the guage in the tank? Sparks usually occur where the short is.
They never attempted to explain schematically or otherwise any mechanism to explain their theory.
Secondly, what data gets recorded in the black box? They said all data looked normal. Does the fuel level of the auxiliary tank get recorded? If so, and a high voltage wire came in contact with the fuel guage wire, wouldn't the fuel level reading have jumped just before the spark?
I haven't had time to do much reasearch on the discussions contained in this website do forgive me if these questions have been covered before.