Order
to airlines would follow advisory from the plane's maker about
danger of using pumps
Thursday,
April 12, 2001
By JAMES
WALLACE
SEATTLE POST-INTELLIGENCER REPORTER
The Federal Aviation Administration is
expected to order the nation's airlines to adopt new safety
procedures that would further reduce the chances of a fuel-tank
explosion on Boeing's 737, the world's most often-flown jetliner.
An industry source said last night the
federal agency will issue an emergency airworthiness directive,
perhaps as soon as this week, as a result of the explosion last
month of the center fuel tank of a Thai Airways 737 at the Bangkok
airport.
The directive would order airlines not to
operate two fuel boost pumps in the center tank when the tank does
not have fuel in it.
Those pumps were running on the Thai jet
even though the center tank was empty, the source said.
The National Transportation Safety Board,
in a statement yesterday, said there is no evidence the explosion
of the center fuel tank was caused by a bomb or sabotage.
The board also said the air conditioning
units on the Thai jet had been running continuously for about 40
minutes while the jet sat on the ground at the Bangkok airport on
a hot day.
It is the third known incident since 1990
-- including the TWA Flight 800 catastrophe -- in which the center
fuel tank of a Boeing plane blew up after air conditioning units
ran for a long time while the planes sat on the ground on a hot
day.
Even though fuel tanks explosions are
very rare, the safety board has been concerned for some time that
a spark inside the center fuel tank could ignite fuel vapors if
those vapors are heated to explosive levels.
The air conditioning units are located
under the center fuel tank on Boeing-made planes, and the heat
given off during ground
operations can be get into the tank, raising the temperature of
fuel vapors.
A flight attendant was killed and several
other people were injured by the blast on the Thai jet, which was
first thought to have been a bomb planted to kill the Thai prime
minister. He and his son were waiting to board the jet with the
other passengers.
Boeing last night sent a telex to all 737
operators recommending the fuel boost pumps in the center fuel
tank not be used when the tank is empty. The FAA's airworthiness
directive is expected to mirror the Boeing telex but make the
recommendation mandatory, the industry source said.
The boost pumps are used to transfer fuel
from one tank to another.
It is not known what role, if any, the
pumps played in the explosion on the Thai jet.
What is known from the board's statement
yesterday is that fuel vapors in the tank would have been heated
by running the air conditioning units for so long while the jet
was on the ground.
All of Boeing's planes except the 717,
formerly the McDonnell Douglas MD-95, have the air conditioning
directly below the center wing tank.
McDonnell Douglas jets have air
conditioning units in the front or rear of the plane. Airbus jets
have air conditioning packs under the center wing tank, but the
design incorporates a cooling system.
The safety board last year criticized the
design of Boeing jets because of the placement of the air
conditioning units and the lack of a ventilation cooling system.
The criticism came as the board ruled
that fuel vapors in the center wing tank of TWA Flight 800 had
been heated to explosive levels because the air conditioning units
on the 747 had run for more than two hours while the 747 was
parked on the ground. The tank exploded about 13 minutes after the
jet took off from Kennedy airport on a flight to Paris July 17,
1996, killing all 230 aboard.
The board said a spark of unknown origin
in the tank apparently ignited the vapors. Had the vapors not been
heated, there would have been no explosion, the board said.
Until last month's explosion on the Thai
jet, the only known 737 center fuel tank explosion was that of a
Philippine Airlines jet in 1990 at the Manila airport. The
explosion killed eight people.
As was the case with the Thai jet, it was
a hot day and the air conditioning packs on the Philippine
Airlines jet had been running for some time when the fuel tank
blew up as the plane was being pushed back from the gate.
Last May, Boeing recommended in a service
letter to operators of its jets that air conditioning units not be
turned on when a plane is on the ground if the outside air
temperature is higher than 60 degrees. The FAA subsequently issued
an informational bulletin to FAA representatives assigned to each
air carrier encouraging the application of Boeing's
recommendations.
But the FAA did not issue a rule that
would make Boeing's recommendation mandatory. That could change as
a result of the Thai explosion, according to people familiar with
the matter.
The Seattle Post-Intelligencer reported
two weeks ago that the investigation of the Thai Airways incident
was focusing on a center fuel tank explosion and not a bomb.
In its statement yesterday, the safety
board said the accident occurred at 2:48 p.m. on a day with
temperatures the high 90s. The initial explosion of the center
tank was followed 18 minutes later by an explosion in the right
wing tank, the board said.
"Air conditioning packs, which are
located directly beneath the center wing tank and generate heat
when they are running, had been running continuously since the
airplane's previous flight, including about 40 minutes on the
ground," the board said.
The safety board last year strongly
recommended that inert nitrogen gas be pumped into jetliner fuel
tanks to lessen the danger of an explosion.
That recommendation is still under study
by the FAA.
The FAA has said that computer modeling
shows that a flammable fuel and air mixture exists in the center
fuel tank of commercial jetliners about 30 percent of the time.
That would only be reduced to about 25
percent by not running air conditioning units when a plane is on
the ground, according to the FAA.
But pumping inert nitrogen into tanks
would dramatically reduce the time a dangerous fuel mix is present
to about 2 percent, the FAA has said.
The FAA is studying a ground-based system
that would pump inert nitrogen into the center fuel tank before
takeoff. The cost of that system would be about $1.6 billion over
13 years and would take three years to implement on all U.S.
jetliners.
The agency is awaiting a final report by
an aviation rule-making advisory committee before deciding how to
proceed. That report is expected by July.
P-I reporter James Wallace can be
reached at 206-448-8040 or jameswallace@seattle-pi.com
http://seattlep-i.nwsource.com/business/18352_boeing12.shtml
