NEW YORK (USA) - It happened half a world away. A Boeing 747 exploded in
midair 20 minutes after taking off in Taipei, Taiwan, killing all 225
aboard. In the United States, there was the usual flurry of news stories
but little sustained interest in a crash that did not involve U.S.
But the aviation industry and federal safety officials are paying
close attention to the May 25 crash of China Airlines Flight 611. It's
too early to tell why the 23-year-old plane broke apart with no warning.
The circumstances have raised the possibility that the culprit could
have been the same design flaw that brought down TWA Flight 800 six
"Everybody's watching this one," said Robert Clodfelter, an
explosions expert and consultant in Dayton, Ohio.
It will be weeks or months before investigators will be able to tell
if the center fuel tank exploded on the China Airlines plane as it did
on the TWA plane, also a Boeing 747. All that is known of the China
Airlines flight is that the plane took off at 3:08 p.m., climbed to more
than 30,000 feet and disappeared from radar at 3:28. There were no
distress calls. Military radar recorded the aircraft breaking into four
The two black boxes that record flight data and cockpit conversations
have not yet been recovered. And most of the wreckage still lies beneath
130 feet of water in the Taiwan Strait between Taiwan and mainland
China. Investigators won't know more until the boxes and the wreckage
In addition to the fuel tank scenario, investigators will be looking
into several possibilities: a catastrophic structural failure, the
failure of a door locking mechanism, or a bomb.
Authorities with the Taiwan government, which is leading the crash
inves- tigation, earlier made statements that atmospheric conditions at
30,000 feet would make a fuel tank explosion impossible. But experts say
that's not correct.
"I'm sitting here looking at the data," said Joe Shepherd, professor
of aeronautics at the California Institute of Technology, noting that
the federal government and the industry have known for more than 30
years that an explosion could take place at high altitudes. Shepherd
studied fuel-air explosions for the National Transportation Safety Board
after the Flight 800 crash.
On the ground, air conditioning packs beneath the fuel tanks of the
747 and other Boeing jets can heat up the fuel vapors in a nearly empty
center tank to the flammable state. When the plane takes off and climbs,
the pressure decreases and with that the temperature range at which the
vapors are flammable decreases as well. At the same time, the tank is
cooling as the aircraft climbs into the colder air of the upper
atmosphere. As the temperature decreases, along with the pressure, the
vapors can remain flammable until sometime during the cruise portion of
the flight when the tank becomes too cold.
Once the vapors ignite, an explosion of the tank is inevitable. And
the tank, located between the wings, is a major structural part of the
The Federal Aviation Administration has issued dozens of orders to
airlines to make fixes to prevent the ignition of the vapors. But the
NTSB believes that it's impossible to identify all the ignition sources
and that the only real fix will come with preventing the buildup of
The FAA and the aviation industry have predicted between two and
three fuel tank explosions in a 10-year period. Last year, the center
fuel tank of a Thai Airways Boeing 737 - which has a similar tank design
to the 747 - exploded while the plane was on the tarmac in Bangkok.
The safety board sent a five-person team to aid the investigation.
Boeing sent three investigators to the scene and will send more when the
wreckage is retrieved.
"We're holding back the main team until we know what we're looking
at," said Boeing spokeswoman Liz Verdier. "We need to find out the
answer and see if it's something that needs to be changed."
In March, an industry group that advises the FAA told the agency that
methods to prevent flammable vapors in fuel tanks are effective but too
expensive to justify. The FAA is continuing to study ways to put
nitrogen in fuel tanks to keep the vapors from igniting.
"With all the work the industry did ... we still don't know that
anything they've done will prevent another fuel tank explosion," said
Kevin Darcy, a former accident investigator for Boeing who worked on the
Flight 800 probe. "I'd be a little bit anxious if I were Boeing or the