FAA Proposes Less-Stringent Regs Ahead Of 787 Certification

The FAA is apparently stepping back from regulations governing fuel tank fire standards, a move that, if approved, will benefit the certification effort of Boeing's upcoming 787 Dreamliner.

The Seattle Times reports the FAA recently decided to relax fuel tank safety regulations brought about by the 1996 downing of TWA 800, which investigators ruled was due to a spark igniting fuel vapors in the empty center wing tank of a Boeing 747-100.

The regulations in question are tied to the DOT rule -- enacted in 2001, but mandated last year -- that all commercial aircraft operating in the US must have systems installed by 2010 to render fuel vapors inert. A related proviso states all new airliners must have three redundant safety systems in place to prevent sparks from occurring within the fuel tank.

The FAA pushed for those standards to be implemented... but now calls them "impractical," and says only one backup should be required to be in place on some parts, not two.

The FAA's proposal came about after Boeing said its new composite-bodied 787 wouldn't be able to meet the stricter standards, throwing another wrench into what has already been a frustratingly drawn-out development effort.

"Boeing spent years trying to develop triple layers of structural lightning protection for every 787 fuel-tank fastener and joint, but we were unable to identify the technical means at many locations in the wings," said one of two lightning experts who spoke with the Times, on the condition they not be named.

Roughly 190 FAA engineers working on the 787 certification, most of them former Boeing employees, have cried foul with the FAA's proposal. Those engineers, represented by a separate chapter of the National Air Traffic Controllers Association, say there are three areas of concern with the 787 wing that make it vulnerable to sparks caused by lightning strikes.

They say the aluminum shear ties that attach wing ribs to the spars are susceptible to cracking, exposing an area where sparking could develop. They are also concerned with the possibility a wing-skin fastener could also break, popping the sealant used and, once again, exposing the internal structure. Finally, sealant used on fasteners inside the fuel tank could break up over time, exposing a gap between the fastener head and the surrounding sleeve.

Boeing replies it has studied those matters closely, and has already implemented fixes after problems were found in earlier testing. The two Boeing experts say shear-tie cracks or broken fasteners have not proven susceptible to sparking.

In the case of the sealant issue, the way fasteners are installed in the fuel tank was completely changed, by putting the heads on the outside of the tank, not inside. For fasteners that couldn't be changed, an extra coat of sealant was used.

"The [sealant] issue is totally resolved now," said one of the lightning experts. "The level of detailed design, test, and analysis (in the 787's wing-tank lightning protection) ... is greater than has been conducted previously in aviation," added the other.

NATCA -- which, it must be noted, is at loggerheads with the FAA over other issues, as well -- calls the FAA's seeming reversal on its own rules "an unjustified step backward in safety," adding the relaxed rules could leave a commercial airliner "one failure away from catastrophe" when flying around lightning.

Not surprisingly, Boeing's experts counter the system is completely safe. "I wouldn't hesitate to get on the plane," said one. "I know more about the structural protection on this airplane than I do on anything else we've ever built."

Ali Bahrami, the head of the FAA Transport Airplane Directorate in Renton, believes the wing fastener rule as it stands is too strict. Bahrami notes two new aircraft certified since the rule went into place -- the Dassault Falcon 7X and the composite-bodied Hawker 4000 business jets -- needed to have exemptions granted to be certified out of compliance with the regulations.

"To this day, we have not had one manufacturer that has been able to demonstrate compliance with that rule," said Bahrami. "We decided it's time to re-evaluate our approach."

The FAA has claimed the less-stringent standards for fastener sparking is offset on the 787 by another feature called for by the DOT: its fuel-vapor inerting system, which pumps nonflammable nitrogen gas into fuel tanks as the level of fuel inside drops. The 787 will be the first new-design aircraft to be equipped with such a system.

However, there's a catch there, as well. Contrary to the FAA's original rule, the 787 system will not be required to be "full time." If the inerting system breaks down, the operating carrier will be allowed to fly the plane in revenue service for up to 10 days while it waits for the needed parts.

If implemented, the FAA's new regulations would benefit all manufacturers of commercial aircraft, not just Boeing... but Tomaso DiPaolo, in charge of NATCA's aircraft certification branch, questioned the FAA's motives on easing the regulations in response to testing on the 787.

"It's another example of the FAA getting too close to industry," he said. "It appears that whatever Boeing wants, Boeing gets."

FMI: www.boeing.com, www.faa.gov, www.natca.org