Technological advances helped push inerting measure
This story was reported by Bill Bleyer, Tom Brune, Keith Herbert and
Jennifer Smith. It was written by Bleyer.
July 18, 2008
When TWA Flight 800 exploded off Long Island 12 years ago, the only
available system to prevent ignition of fuel vapor in aircraft weighed
more than 300 pounds.
Now research by the Federal Aviation Administration and the industry has
produced equipment as light as 106 pounds.
That reduction in weight, with a corresponding decrease in complexity,
size and cost, is one of two key technological breakthroughs that
allowed the FA A on Wednesday to announce a rule to require airlines to
install "inerting" devices for passenger jets with center fuel tanks.
The equipment makes explosions in empty tanks highly unlikely by
replacing some of the oxygen with nitrogen.
At the time of the Flight 800 crash, the only available technology was
being used on military jets. It was large, heavy and expensive. But the
government wasn't concerned about cost or size on military transport
Size and cost would be important for commercial carriers, however, so
the FAA convened the first of two committees in 1997 to look into a
system that would work for passenger jets. The experts reported back in
1998 that there was no practical or affordable way to do it. The second
committee concurred in 2001.
But the FAA continued with its research in laboratories in Seattle and
near Atlantic City, and two eureka moments led to Wednesday's action.
"What made it affordable was the development of a lightweight nitrogen
generating system" by FAA engineers aided by other experts in 2002, said
John Goglia, a former National Transportation Safety Board member who is
now a Washington aviation safety consultant. "That was the first
First, it eliminated all of the moving parts in the military system. And
the weight of the units dropped to about 106 pounds for a Boeing 737 and
257 pounds for a Boeing 747 like Flight 800.
Second, a higher percentage of oxygen could be allowed -- 12 percent
instead of 10 pe rcent -- without increasing the risk of an explosion.
The insight was based on Navy research on its jets.
That allowed the inerting equipment to be even smaller, lighter and
After those breakthroughs, the FAA was able to announce in 2004 that it
planned to require a system to reduce the vapor risk and make a proposal
the following year. It then took the agency three more years to adopt
the rule over the objections of aviation trade groups.
An increasingly small price tag helped seal the deal. When it first
raised the idea of eliminating the vapor threat, the FAA calculated that
retrofitting all of the existing aircraft and installation of equipment
on future jets would cost $35 billion. The cost of the final proposed
change is estimated at $1 billion, FAA spokeswoman Alison Duquette said.
The rule will affect 2,730 aircraft built after 1991 -- 55 percent of
the U.S. passenger airliner fleet -- and all similarly designed jets
built in the future. Boeing and Airbus, the only aircraft makers who
used the center-fuel-tank design after 1991, now have nine years to make
the retrofits. By 2010, all new aircraft with center fuel tanks must
have the new safety equipment.
To get the industry even reluctantly onboard, "the FAA also gave up a
lot," Goglia said. "Airplanes built before 1991 are exempt" and that
covers almost all of the McDonnell Douglas MD80 fleet and much of the
Boeing 747 fleet.
Evidence of a Missile
Flight 800 Database
Bomb -------- 4%
Fuel Tank --- 14%
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