It has been 12 years since Trans World Airlines experienced the loss of a 747 that had departed JFK airport bound for Paris. All 230 passengers and crew onboard TWA Flight 800 lost their lives on that hot July day in 1996.
Nothing about that accident was routine or easy, and the subsequent accident investigation became the most expensive in U.S. history. First there was the search for possible survivors, followed by the recovery of the victims, then the mapping of the debris field, which was under 120 feet of water. Then investigators had to raise the des-troyed aircraft and relocate the pieces to a facility several miles from the crash site.
As time progressed and no cause became evident, the press latched on to
the story, and some wild possibilities emerged. Many involved the theory of a massive cover-up by the U.S. government. The NTSB eventually determined that the center wing tank of the airplane had exploded, resulting from the ignition of
the flammable fuel-air mixture in the tank. Nonetheless, it seems that every year around the anniversary of the July 17 accident another theory of what happened–along the same lines–finds its way into print. Some of them make for interesting reading, but the physical evidence most often disproves these theories.
The FAA added a new dimension to the investigation last month when it published the final rule on fuel tank inerting, which stems from a Safety Board recommendation. Fuel vapors inside a tank need to mix with oxygen to ignite. The oxygen range is approximately 12 to 20 percent. If you can find a way to keep the vapor out of this range, the likelihood of an explosion diminishes considerably.
Finding a way to inert fuel tanks to this level proved a challenge until the FAA developed a cost-effective way to generate nitrogen. There were several other challenges that delayed adopting this technology for some time, but the FAA now believes that the technology is far enough along that it should be required.
This new rule, along with the approximately 100 Airworthiness Directives and more than 60 Advisory Circulars, will go a long way toward reducing the risk of losing another aircraft in the way we lost TWA 800. This reduction of risk comes with a price tag of about $1 billion. That’s a big number considering how much money the commercial aviation sector has lost over the last few years. However, the protracted time period allowed for compliance will soften the impact somewhat.
Costs Are High but a Necessary Investment
Many in the industry were not impressed with the rule and have been vocal about its cost and the expected impact on the hull loss rate. The FAA believes that without this rule there could be nine hull losses over the next 50 years. Many from the industry believe that estimate to be high.
I believe that it is time we reduced the risk of another aircraft hull loss from fuel vapors. Even with a number of aircraft exempt (Boeing 727s, 717s and some 777s and 767s, as well as the Airbus 320 series, the A330 and the A380) from this rule, the impact is substantial. Cargo operators are exempt from retrofitting their existing fleet but will be required to comply for new aircraft and future conversions will be required to maintain a previously installed system.
The technology that will allow the inerting of the fuel tanks has an equally important–but less discussed–additional benefit. For some time a number of people in the industry have been concerned about cargo fires in passenger aircraft. We had a number of debates and finally a rule after the ValuJet 592 accident in the Florida Everglades in 1996. Most industry people realize we need to find a replacement for halon as soon as the supply is diminished.
Nitrogen could be used to lower the oxygen levels inside aircraft cargo areas, preventing a fire from starting. This is clearly a much better option than trying to extinguish the fire once it has started. Remember: we need only to reduce the oxygen level, not eliminate the oxygen completely. If you look at the number of transatlantic and transpacific flights where cargo fires are a concern, you quickly realize the importance and benefits of such a system.
Over the next few months I am sure that we will see much discussion about this rule, but one thing is clear: by the end of this, we will all travel with a reduced risk of explosion or fire onboard our aircraft.