Look Out, Your Fuel Tank May Be Exploding - Again
What excuse will the FAA and industry give us the next time hundreds of families suffer the needless loss of their loved ones?
Ten years after TWA 800 exploded over Long Island killing all aboard and thirty two years after its sister ship exploded over Madrid killing all aboard, the FAA still has no rule in place to require inerting of transport aircraft fuel tanks. The FAA claims only four aircraft will explode from this cause in the next fifty years. That’s an interesting statistic given that no less than 18 and probably more have exploded in the thirty five years since jet transports have taken over the skies.
While some manufacturers like Boeing whose airplanes have done the exploding say they will inert tanks of all new airplanes, Airbus says it will only do so if required because its airplanes haven’t exploded yet.
The original fuel tank engineering philosophy was to prevent explosions by keeping sparks away from inside partially filled tanks. That was honored more in the breach since fuel quantity sending units, electrical wires and fuel pumps were inside the tanks. How the manufacturers intended to meet the requirement to avoid sparks is inexplicable.
When the sister ship to TWA 800, then in the Iranian Air Force, blew up on approach to Madrid in 1974, the cause was assigned to a lightning strike on the near empty fuel tanks.
Then when the inquiry was over for that crash an industry task force was assembled to discuss the ways fuel tank explosions could be avoided in large aircraft fuel tanks. Nothing ever came of it but the military by that time was already providing fuel tank inerting in aircraft that could be hit by incendiary rounds to prevent explosions. In fact a military DC-9 was equipped with a nitrogen inerting system even before the Madrid crash and it worked well and was cheap and uncomplicated to install. Other military aircraft such as the C-17 actually manufacture nitrogen in flight and it is then used to inert its fuel tanks as the fuel is consumed.
Since TWA 800 a number of FAA Airworthiness Directives have been issued to tidy up the electrical issues in the tanks but they by design still remain dangerous. A cartoon published soon after TWA 800 showed a charicature of Grandma Moses rocking in her chair with the balloon saying: “Why would anyone route wires through the middle of a fuel tank anyway?” Common sense would have dictated that no wiring of any kind be allowed in the tank even if the regulations didn’t already imply that.
So the design philosophy changed to now require that the space between the fuel and the top of the tank be inerted so it won’t explode. Industry was asked to come up with proposals and they did much like they did thirty years earlier. None have been implemented so the risk remains.
What is even more indefensible is that there were immediate steps that could have been taken and some were and most were not to prevent explosions in the short term. Carrying more than a few gallons of fuel in large fuel tanks was no longer permitted in the hope that dangerous fuel molecule concentrations would not occur. Limiting the use of air conditioning packs on the ground that use the center tank fuel as a heat sink was discouraged to avoid temperatures in tanks getting to the lower explosive limit.
But use of cabin air that is sent overboard and routing it through the tanks instead so as to make the fuel air mixture too lean to explode was not required. That would have been cheap, expedient and worked in the short term before a more effective solution was engineered.
Thus after more than thirty years the risk is just as high that an aircraft the size of a Boeing 747 will explode killing all aboard for the very same reason that TWA 800 and the sister ship did, a bad fuel tank design coupled with inadequate inerting of the vapors in the tank.
What excuse will the FAA and industry give us the next time hundreds of families suffer the needless loss of their loved ones? None will suffice. None did suffice. None should suffice. The victims of TWA 800 should not have died in vain.
- Arthur Alan Wolk
