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."