What's the Likelihood of....
It's beginning to look like an Al Qaeda plot.
I still reckon that, because of the mis-wiring, the pumps are probably finding another earth (courtesy of the short or a further miswiring) - and running on continuously, wet or dry (the cockpit indicator would show it as OFF once power to it via its switch has been cut). Once you short something out it normally overheats; a conductor or terminal strip then melts (usually with a loud bang) and that's what's meant by "shorting out" (assuming CB doesn't do its job). However submerge that same part in fuel most of the time and it doesn't get hot enough for the electrics to melt (fuel rapidly dissipates the heat). What can happen (so the theory goes) is that (instead) the rapid heat build-up caused by the shorting permeates throughout the metal pump and, due to different coefficients of expansion the pump starts binding and so the heat build-up within it increases even more. However as long as it's submerged in fuel, there's enough cold-soak that there's no sufficient localised heat build-up such as to cause any electrical component to melt, "short out" - and so cut the current.
End result is a "blueing" of the metal indicating that extreme localised frictional heat has occurred - mainly due to the binding occurring whilst power remains on to a very hot pump (which is what they've found). And of course in any such shorting situation there would be no CB to overload and blow. Just a theory.
November 27, 2002 - FAA Issues 3rd Warning on Fuel Pumps
WASHINGTON (USA) - The Federal Aviation Administration is requiring about 3,500 Boeing jets to fly with extra fuel to prevent fuel pumps from overheating and possibly causing an explosion.
The FAA has sent airlines three safety warnings about the problem since August. The latest was issued last weekend after pumps in three planes overheated, the FAA said Tuesday.
The warning is intended as a precaution while the FAA figures out what's causing the problem with the pumps, made by Hydro-Aire Inc. of Burbank, Calif.
James McKenna, managing editor of Aviation Maintenance magazine, said the FAA doesn't ordinarily need to make a third attempt to ascertain what's wrong.
"That tends to unsettle the FAA,'' McKenna said.
No serious problems have been linked to the problem. However, if a pump overheats, the right mixture of temperature, oxygen and fuel can cause an explosion, McKenna said.
FAA spokesman Paul Takemoto said the extra fuel eliminates the possibility of an explosion.
"There's no danger of (the pumps) igniting fuel vapors if they're covered,'' he said.
The warning will remain in effect until the agency determines what causes the fuel pumps to overheat, Takemoto said.
The order affects about 1,400 planes - 737s, 747s and 757s flown by U.S. carriers. The FAA is also sending the advisories to its counterpart agencies overseas, covering another 2,100 jets.
The National Transportation Safety Board ruled that an explosion in the fuel tank of TWA Flight 800, a Boeing 747, caused it to crash off the coast of Long Island in 1996, killing 230 people. Vapors in the partly empty tank probably were ignited by a spark in the wiring, the NTSB said.
In August, the FAA ordered airlines to submerge certain Hydro-Aire pumps with fuel or, if not, to X-ray them to make sure they were properly wired. If they weren't, they had to be replaced.
Major U.S. carriers said they had few planes in which the suspect pumps were installed.
In September, the FAA found the problem potentially included every Hydro-Aire pump and ordered all fuel pumps submerged or X-rayed and replaced if faulty.
Then, last week, Boeing Co. received reports of overheating in fuel pumps that had been replaced on a Singapore Airlines 747 and on a Lufthansa 747.
The overheating of those pumps wasn't caused by faulty wiring, said Boeing spokeswoman Cindy Wall.
A pump on a third plane had been removed and was found to have overheated during an inspection.
"It's baffling,'' Wall said. "They've been working nonstop 24 hours a day trying to fix it.''
Hydro-Aire President Greg Ward said the company has made the pumps for 30 years without a problem. It's conducting an extensive investigation that includes chemical analysis of pump parts that overheated, checking airline service records and interviewing retired employees who worked on the pumps, he said.
"We're still piecing together clues,'' Ward said.