the fixable problem that may be here to stay
By Air Safety Online
In most respects, July 17, 1996 was to be just another day for N93119,
an ancient, 25-year-old Boeing 747-100 jetliner sitting on the tarmac
at New York's John F. Kennedy International Airport, scheduled for
an evening flight across the Atlantic.
On his last assignment with ABC Sports, producer John O'Hara hurriedly
made his way through the airport to catch a flight to Paris to supervise
coverage of the Tour de France. The 39-year-old five-time Emmy Award
winning journalist was taking his wife Janet and daughter Caitlin
along for the trip, while his sons Brian and Matthew stayed at home
O'Hara boarded the plane just moments before the scheduled takeoff
The packed 747, with its fading "Trans World" titles, was
airborne by 8:20 PM. O'Hara and 229 others aboard Flight 800
never made it to Paris.
|Wreckage from Flight 800 is seen
the waters off Long Island, New York. (AP)
"The crash of Flight 800 graphically demonstrates that, even
in one of the safest transportation systems in the world, things can
go horribly wrong," announced Jim Hall, a modest, former political
aide with a slow Tennessee drawl, to a crowd of hundreds gathered
at the National Transportation Safety Board headquarters in Washington,
It was August 22, 2000 when the NTSB released their official 'probable
cause' of the crash of TWA Flight 800, which occurred more than four
The cause of the 1996 crash, the NTSB concluded, was an explosion
in the aged aircraft's center fuel tank.
"The bottom line is that our investigation confirmed that the
fuel-air vapor in the center wing tank was flammable at the time of
the accident, and that a fuel-air explosion with Jet A fuel was more
than capable of generating the pressure needed to break apart the
center wing tank and destroy the airplane," Bernard Loeb, then
Director of Aviation Safety at the NTSB, said at the hearing.
Philippine Airlines Boeing 737 similar to this one was
involved in an accident similar to TWA Flight 800 in 1990.
Six years prior to the TWA crash, the NTSB had investigated an accident
involving a Philippine Airlines 737-300 jetliner in the South Pacific.
The plane, which had been sitting idle on a hot runway for hours,
was packed with passengers. Nine were killed when the plane's
center fuel tank exploded.
Using data from the Philippine and TWA accidents, the NTSB theorized
that if an aircraft's center fuel tank were hot enough -- NTSB tests
proved that the tanks could reach temperatures in excess of 200 degrees
Fahrenheit -- and if the tank was relatively empty, remnants of fuel
could turn into an extremely explosive vapor.
But warm weather alone cannot create this type of explosive vapor
in fuel tanks. What other factors contribute to an overheated
"Air conditioning," said Christine Negroni, a former CNN
aviation correspondent and author of Deadly
Departure: Why the Experts Failed to Prevent the TWA Flight 800 Disaster
and How It Could Happen Again.
Located directly beneath the center fuel tank of the Boeing 707,
737, 747, and 767 jetliners are large air conditioning units, which
can heat up to hundreds of degrees, effectively heating the fuel tanks
above as well.
The TWA 747 had been sitting on the tarmac at JFK Airport for more
than two hours, and it was summertime; July. Temperatures on
the 17th of July in New York reached well into the 80s.
The Philippine plane had also been sitting for hours in hot weather
as well, with the air conditioning packs running the entire time.
And there have more incidents involving Boeing planes.
Temperatures in the early afternoon of March 3, 2001 reached into
the high 90s in Bangkok, Thailand. At Don Muang International
Airport, a Thai Airways Boeing 737, registered HS-TDC, was being prepared
to fly Thailand's Prime Minister Thaksin Shinawatra and his son, as
well as more than 140 other passengers to the northern city of Chiang
The 9-year-old jetliner's air conditioning packs had been running
for 40 minutes on the ground at the airport, as well as during the
entire previous flight.
Minutes before passengers were to be boarded, the center fuel tank
exploded. 18 minutes later, the plane's right wing tank also
exploded, and the resulting fire destroyed the aircraft.
One flight attendant was killed, and seven others were injured in
the blast. The National Transportation Safety Board and Boeing
are assisting the Thai government in the investigation.
The burnt-out Thai Airways Boeing 737 is pictured sitting
on the tarmac at Don Muang Int'l Airport in Bangkok. (AP)
In a press release dated April 11, 2001, the NTSB made note that
the Thai accident was frighteningly similar to the Philippine Airlines
accident eleven years earlier.
"The recording of the HS-TDC explosion has features that are
similar to recorded features of a Philippine Airlines 737-300 center
wing fuel tank explosion in May 1990. Neither recording includes
a precipitating sound of an initiating explosion that may have ignited
the fuel tank," the release said.
"What Boeing has found was some problem with the air conditioning
system but they are not sure. It may have been caused by explosives
because of traces of C-4 explosives," Prime Minister Thaksin
FBI labs later found no traces of explosives, and a Boeing spokeswoman
said Boeing never made any such comments relating to the air conditioning
system on the Thai jet.
"It's painfully obvious that this really is a problem, and the
NTSB realizes that," Christine Negroni, who has been studying
the effects of overheated fuel tanks for years, told Air Safety Online.
"The thing that all of these aircraft have in common is that
they have heat elements directly below the center fuel tanks,"
Negroni said, noting that the NTSB has been trying for years to make
this a public issue.
Says Negroni, "This is like a tree falling in the forest, the
reason that the NTSB is making this as poignant an issue as they are,
is because it doesn't matter how much they say we have a problem,
nobody wants to do anything about it."
Negroni may be right. The Federal Aviation Administration has
issued no directive in recent years, that Air Safety Online could
immediately locate, regarding the use or position of air conditioning
units on Boeing jetliners.
According to Negroni, Boeing has known of the dangers of heated fuel
tanks and the placement of the air condition packs for a long time.
decided not to reposition the air conditioning units in later
models of the Boeing 737 and 767. (Boeing)
"The 707, 737, 747, and 767 center fuel tank design issue has
been a known problem for 35 years, and nothing is being done about
"Many at Boeing throughout the 1980s thought that in retrospect,
maybe the air conditioning pack under the center tank design wasn't
such a good idea, but Boeing continued to make these bad decisions,
and bamboozled the FAA to go along with it," Negroni said.
The National Transportation Safety Board, however, has presented
this issue to the FAA at least three times in the past twenty years,
and they are running into trouble making this a more public issue.
Perhaps if the Philippine and Thai events had resulted in larger
accidents, the issue would have become more public.
"The only thing that makes these non events is that the planes
were parked on the ramp. Just because Thailand's Prime Minister
wasn't killed in the accident, that doesn't mean this isn't a real
alarm, but it still makes it hard for investigators to convey such
a message," Negroni said.
"It's important to understand that when an airborne aircraft's
center fuel tank explodes, that plane is going down. It's only
luck that these two aircraft weren't airborne."
In 1998 and 1999, the Federal Aviation Administration mandated that
U.S. airlines install additional shielding on wiring in and around
the center fuel tanks of older Boeing jets. This, the FAA acknowledged,
would reduce the risk of a spark causing an explosion in a tank with
Only now are authorities beginning to look for ways to prevent the
heated vapors from being created.
In July 2000, the FAA launched a fuel tank inerting study, in which
a Boeing 737, equipped with special sensors, would be used to test
the effectiveness of a system that pumps nitrogen into the fuel tank
while the plane is on the ground.
The fuel tank inerting system uses
nitrogen to separate fuel residue from
air vapor in heated fuel tanks.
This is part of an FAA study that began in 1999 to determine how
nitrogen could be pumped into planes at airports with a system that
uses a membrane to separate nitrogen from air.
The nitrogen inerting system could prevent explosive fuel vapors
from filling empty fuel tanks. In fact, the United States Air
Force has been using a similar system on their aircraft for years.
Unfortunately, it took the loss of more than 240 lives over 35 years
to generate enough awareness for the FAA to begin an official study
on the issue.
It's a clear-cut case of what aviation industry insiders call "Tombstone
"The thing that all these aircraft have in common is that they
heat elements directly below the center fuel tanks. We need
to get rid of either the heat elements or the vapors, and we need
to do this now," Negroni said.
The Boeing Commercial Aircraft Group did not change the location
of the air conditioning packs in its newest 737NG ("new generation")
or 767-400 jets, still directly underneath the center fuel tanks.
Meanwhile, Boeing told all 737 operators they should not use fuel
boost pumps in the center fuel tank when the tank is empty, the Seattle
Post-Intelligencer reported. Boost pumps transfer fuel from
one tank to another.
Boeing also issued a service letter in May of 2000, as a result of
the TWA crash investigation, asking operators to use ground source
air conditioning, which does not use the aircraft's air conditioning
The Federal Aviation Administration is expected to issue an airworthiness
directive soon making the recommendation mandatory, the newspaper
said, citing an unnamed industry source.
"The air conditioning packs are a known heat source," said
Liz Verdier, a spokeswoman for the Boeing Company. "We
know that these aircraft exploded, but there are many other factors
other than the air conditioning packs that must be looked at to determine
the exact ignition source in these accidents."
"We still haven't found any one cause for all of these fuel
tank explosion accidents. As we continue
these investigations, there may be more causes found, and we will
work to fix those," Verdier said.
"Boeing is actively working with the FAA to make fuel tanks
as safe as possible," Verdier said, adding, "These aircraft
have been flying safely for years and years. If we can make
them even safer, we will."
Before the fuel tank inerting program can be implemented, the FAA
must complete a "Cost of Implementing Ground-Based Fuel Tank
Inerting in the Commercial Fleet" study to determine whether
the additional level of safety is economically feasible for U.S. airlines.
The FAA on fuel tank inerting