When Flight TWA800, a 747 Classic, exploded in 1996 just after take-off from JFK the reconstruction found that the epicenter of destruction had been the center wing tank (CWT). Although admittedly a rare event, the NTSB was concerned that yes, heated fuel fumes in a near empty tank were quite explosive. In the ten years that have passed since then the solution began as “finding and deleting ignition sources” but then progressed to neutralizing the explosive atmosphere within the tank. An extensive program of electrical validation concluded that it was impossible to guarantee that a spark couldn’t ignite any heated ullage vapors. Having initially claimed that tank inerting by nitrogen would be impractical, the FAA then became aware of a new technology that would allow nitrogen enriched air (NEA) to render the tanks' inflammably inert most of the time. Although not as safe as a nitrogen filled tank, the level of safety achievable was agreed to be acceptable. The FAA then indicated that it wanted to go beyond SFAR88 - the electrical safety measures – and adopt NEA. The logic of this is unassailable. The industry has been in a technological huddle for the last three years on the acceptability of this measure (read “cost”). Meanwhile one further aircraft has suffered a CWT event. Notably all fuel tank exploders have been Boeings.

Not unexpectedly, Airbus see the problem as being little to do with their designs. Having responded to and incorporated the earlier measures, Airbus is loathe to take on board a whole new system for inerting. They may have a point. Although most of the Airbus designs have their airconditioning systems beneath the CWT’s, their design does not result in use of the CWT as a heat-sink (i.e. the unique Boeing design flaw). From their point of view, Boeing does not want to be uniquely saddled with yet another weight penalty and system complexity while seeing its rival get a pass on the requirement. Thus the Association of European Airlines (AEA) and Airbus have adopted a protest position that may yet torpedo the FAA initiative. The comment period for the new proposals has just ended and the expressed European stance has been that accepted cost/benefit criteria have been disregarded in the FAA’s latest Notice of Proposed Rulemaking (NPRM) on fuel-tank safety.

The FAA stance on its proposed “flammability reduction” methods and NEA is that the measures are required to stave off future TWA800 style events. They would apply to existing aircraft as well as newly built designs. The European counter-claim is that the risk of future fuel tank explosions has been exaggerated by a factor of five and the cost/benefit ratio by a factor of 28. Airbus’s NPRM comment questions almost every assumption or statistical projection in the FAA’s latest NPRM. Many of the 3^rd party submissions on the FAA’s NPRM website have been heavily redacted – ostensibly to conceal proprietary data (much of which is Airbus data). It is difficult for any outsider to distinguish the veracity of the arguments. Sandia, long responsible for US nuclear weapons safety, has found fault in many of the conclusions reached. There is altogether an air of dissent, an agreement to disagree and ultimately, very little common ground. A cynic might see the dissent as a convenient pretext for stifling any progress at all. If the FAA was to “go it alone”, there would be arguably two distinct levels of safety in the World’s airliners. This would be a sharp divide and despite the limited degree of harmonization achieved early on in the post TWA800 safety initiatives. In a quite incoherent objection, the AEA also alleges that the NPRM “appears to be driven by National Transportation Safety Board statements and public opinion”. In point of fact the public is likely quite unaware that measures taken post TWA800 have been minimal in comparison with the magnitude of what is proposed.

It was never likely that any consensus would be reached internationally on this issue. The issue itself has become clouded by an invasion of experts and they all come equipped with differing opinions and suggestions. Fuel-tank explosions are an unlikely outcome of heated fuel giving rise to an explosive ullage. Electrical safety has been enhanced – but cannot be assured; removal of ALL ignition sources can only be aspired to. The most assured method of precluding explosions is to inert fuel tanks with nitrogen enriched air. Because of the cost, this fix was going to be strung out to a 2014 implementation. No-one ever factors in the potential cost of delay.

Since TWA800 occurred in 1996, ten years later we would have to call all that’s occurred to date (and all that’s likely to occur in future) little more than a typical FAA gabfest. The risk of a TWA800 repeat, although less now because of the electrical sanitization called for by SFAR88, remains frighteningly real however.