PPRuNe Forums - Fuel tank inerting

FAA site on inerting technologies

http://www.fire.tc.faa.gov/systems/fueltank/hfm.stm

FAA: Jets must be altered
By Alan Levin, USA TODAY
WASHINGTON - The federal government plans to announce Tuesday that it will
require airlines to install safety devices found to prevent fuel-tank
explosions like the one that blew up TWA Flight 800 just off Long Island,
several sources told USA TODAY.
The devices, which flush oxygen from the tanks, will cost airlines millions
of dollars to install.

Oxygen, fuel and heat must be present for fuel tanks to explode.

As recently as 2001, an industry group advising the Federal Aviation
Administration said such devices were not worth the costs.

The FAA order also will address one of the key safety recommendations
prompted by the 1996 accident, which killed 230 people and destroyed a
Boeing 747.

The FAA plans to give airlines seven years to install the devices on
existing fleets, say several sources who have reviewed the proposed action.
Also, the agency plans to order changes in the design of fuel tanks on new
jets to further reduce the risk of explosion, the sources say.

The devices work by slowly pumping non-flammable nitrogen gas into fuel
tanks. If the nitrogen reduces the normal amount of oxygen in the air by
half, fuel won't burn and the tank can't explode.

Since the TWA crash, the FAA has mandated dozens of measures to reduce the
chance of a spark reaching a fuel tank. But FAA officials believe that isn't
enough to prevent all explosions.

The proposed changes would affect all jets in which the center fuel tank is
heated by adjacent equipment. That condition exists about 35% of the time
the aircraft is in operation.

The jets affected include all Boeing models and all Airbus jets. Jets built
by McDonnell Douglas, which was bought by Boeing in 1997, will not require
the changes.

Spokesmen for Boeing and Airbus said they had not seen the FAA's proposal
and could not comment. Airbus has insisted that its jets are not at risk for
fuel-tank explosions. Boeing has already designed a device to protect fuel
tanks on its jets.

One source estimated the proposal could cost $100,000 per jet. The devices
would be installed on about 3,500 jets owned by domestic airlines. That
would bring the costs to roughly $350 million.

The airline industry is in a severe economic downturn, and several sources
said they expect objections from carriers.

Lower cost, higher risk helped alter FAA stance

By Alan Levin, USA TODAY
WASHINGTON - In 2001, an aviation industry group concluded that flushing
oxygen from jet fuel tanks to prevent explosions was prohibitively expensive
and mechanically impractical.
As early as Tuesday, the Federal Aviation Administration was to announce
that it plans to require a device to do just that on all jets vulnerable to
explosions in their center fuel tanks.

What changed in such a short period?

An FAA scientist proved the device could be made relatively inexpensively
and with virtually no moving parts, and the FAA realized that the risk of
fuel-tank explosions was higher than had been believed.

The FAA's move appears to meet one of the key recommendations that was
issued by the National Transportation Safety Board after the crash in 1996
of TWA Flight 800, a Boeing 747 that blew up shortly after takeoff from New
York City. All 230 people aboard died.

The safety board, which investigates jetliner accidents, concluded that a
measure such as injecting non-flammable nitrogen gas into fuel tanks was
needed to ensure the tanks could not explode. The NTSB investigates
accidents but has no power to regulate.

"I think it will be a major, major improvement," said Bernard Loeb, a
retired NTSB official who oversaw the TWA investigation.

Officials say much of the credit for the new requirement goes to FAA
scientist Ivor Thomas. Thomas, a Scottish immigrant, has spent years
studying fuel tanks with Boeing and more recently the government. He oversaw
research at the FAA's William J. Hughes Technical Center near Atlantic City
into devices that extract nitrogen from the air and pump it into fuel tanks.
The non-flammable nitrogen pushes out the air through vents. The oxygen in
air is needed to cause an explosion.

In a key finding late in 2002, Thomas demonstrated that less nitrogen was
needed than previously thought to prevent an explosion.

Air is one-fifth oxygen, and oxygen can cause substances such as jet fuel to
burn or explode. Some military jets contain equipment that pumps nitrogen
into fuel tanks to reduce the oxygen level to 10% or less.

The FAA tests showed that a fuel tank would not explode if oxygen levels
were at 12%. That small difference allowed engineers to design much smaller
nitrogen gas systems, substantially lowering the cost and weight of the
devices.

Boeing, which had argued the devices weren't necessary, jumped on the
bandwagon. It designed and tested its own nitrogen system and intends to
offer it for sale soon, officials said.

Reviews of fuel-tank safety ordered by the FAA also continued to find ways
that tanks could explode. Although fuel-tank explosions are rare (four such
explosions have occurred since 1989), the danger appeared greater than
initially believed.

John Hickey, who oversees aircraft certification for the FAA, said last
summer that the FAA-ordered review had found that nearly all commercial jet
models by Boeing and Airbus were vulnerable.