Thai 737 - not a bomb?

[Biggles Flies Undone]

Deputy Prime Minister Chavalit Yongchaiyudh officially acknowledged yesterday that sabotage played no part in the explosion of the Boeing 737.

Chavalit said that US investigators had found no trace of RDX, the main component of C4 plastic explosive, but Thai officials insisted that they had located explosive chemical agents in the wreckage.

So do we have a problem or not?

[SKYDRIFTER]

STRANGE ONE -

We have a center tank explosion that doesn't destroy the wing center section.

We have a fuel vapor explosion with no ignition source.

We have an entire Boeing fleet with a radical safety defect with no significant inspections or grounding of the fleet, nor a re-designing or retrofitting of the aircraft.

We have a police department which cites a bomb, but the NTSB (not the FBI or equivalent) says no bomb. No RDX = dynamite, TNT, etc.

Yeah, something is wrong in this picture.

It's called, "plausible assertion," Oswald got JFK with one bullet, etc.

[Leanan Sidhe]

Hey SKYDRIFTER,
Didn't we call this one a while back? Maybe now that damned defect will get its long-overdue consideration.

[autoflight]

Have I been missing something here? Is the implication that the explosion was because of some design fault with this model aircraft?

[SKYDRIFTER]

NTSB CLAIMS -

In the absence of an ignition source, the NTSB is seizing on this event to legitimize their claim in their TWA-800 investigation.

The assertion being that the bleed air ducting boils the center fuel tank, creating a potential bomb.

Unfortunately, unless Boeing is violating FAR 25, the situation can't happen as the NTSB claims. [Same investigator as TWA-800, by the way.]

While the Manila fire is unexplained to an appreciable degree, it was a far different event.

[newswatcher]

Here is report, according to CNN:

"A Boeing 737 that exploded on the ground at Bangkok Airport last month shows no traces of a bomb, and investigators are now focusing on the possibility that the explosion originated in the plane's center wing fuel tank, possibly heated by hot air conditioning units underneath it.

A similar scenario helped bring down TWA 800 -- a Boeing 747-100 -- off the coast of Long Island, New York -- during the summer of 1996, killing all 230 people aboard.

The Thai Airways International plane exploded on March 3 -- just 35 minutes before it was to depart with the prime minister of Thailand, prompting speculation that the explosion was an assassination attempt.

But the U.S. National Transportation Safety Board, which is providing technical support to Thailand, said Wednesday, "Despite a thorough examination of the wreckage by Thai and American bomb experts, no physical evidence of a bomb has been found to date."

The 9-year-old Boeing 737-400 was sitting at a gate at Don Muang International Airport in Bangkok when it exploded. A flight attendant aboard the plane was killed and seven people were injured in the blast and subsequent fire, which destroyed the airplane. No passengers were on the plane at the time.

"The accident occurred at 2:48 p.m. on a day with temperatures in the high 90s Fahrenheit," the NTSB 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."

While investigators are quick to say they are far from establishing a cause for the explosion, they acknowlege air conditioning packs were deemed a factor in the TWA 800 explosion.

In that case, the TWA 800 sat on a hot airport ramp with its air conditioners running for more than an hour before taking off. It exploded 13 minutes after takeoff, splintering apart and plunging into the Atlantic.

Last August, the NTSB concluded the probable cause of the TWA 800 accident was "an explosion of the center wing fuel tank, resulting from ignition of the flammable fuel/air mixture in the tank." The NTSB said it could not determine the source of ignition, but that a contributing factor was the placement of the heat-generating air conditioning units under the fuel tanks.

The plane had been delayed for slightly more than an hour on the ground and had its air conditioners running, NTSB records show. The outside temperature was 71 degrees Farenheit.

Nearly a year ago on May 5, Boeing advised airlines worldwide to use ground air conditioning units to cool planes when they are on the ground for extended periods and the temperature is above 60 degrees Farenheit. The advisory did not specify the length of time planes can use their own cooling units while on the ground.

Airlines typically follow the manufacturer's guidance, but are not required to.

The FAA says that it did not issue an Airworthiness Directive, which would have given the voluntary recommendation the force of law. But it did issue a Flight Standards Information Bulletin advising FAA inspectors of Boeing's recommendation.

Boeing spokesman Tim Neale said it is too early to speculate on the cause of the explosion. "There's still plans to do more testing. As we've seen in so many accidents, it can start to look like one thing and then the evidence pops up that shows its something else," Neale said.

The FAA says it has issued or proposed issuing nearly 50 Airworthiness Directives to address safety concerns with center fuel tanks. It also has begun studying ways to make fuel tank fumes inert, rendering them safe from ignition sources.

Former FAA Chief of Staff Michael Goldfard said the similarities between TWA 800 and the Bangkok explosion are only partial.

"The similiarities are that it was a hot day in New York (when TWA 800 exploded). It was a hot day on this crash. The air conditioning system was running in New York. The air conditioning system was running in this crash on the ground which created a flammable mixture. What caused the spark that led to the explosion in this crash ... is yet to be determined.

"There could be a whole host of things that could have happened on that aircraft that led to this crash that has nothing to do with the others," Goldfard said.

The Boeing 737 is "the workhorse of the industry," he said. "It's one of the world's safest aircraft. And so for people who fly this is not one thing they should worry about."

[Leanan Sidhe]

Don't ask me how I got it into my head that SKYDRIFTER and I were on the same page with regard to this...

http://www.pprune.org/ubb/NonCGI/eek.gif They say the mind is the first to go!

The cases of unaccounted for ignition sources causing tank fires/explosions in the 737 series--are rare--but cerainly worth continued investigation.
Knee-jerking to the conclusion that TWA 800 just had to be caused a bomb is no excuse to overlook potential defects in that or any other aircraft.


[This message has been edited by Leanan Sidhe (edited 12 April 2001).]

[SKYDRIFTER]

LEANAN -

Not meaning to cross swords, there are too many questions in the Thai explosion.

There can be no doubt that there was an explosion. One news description describes damage to the tarmac. If it had been the center tank exploding, the wing tips would have sagged, the other tanks would have detonated via the vent system and the adjacent tanks would have been torched from lateral blast force.

If this was the third such case, the FAA would be mandating asbestos shielding above the airconditioning packs.

FAR 25 is quite clear as to the design requirements to protect the center fuel tank; so what can you imagine to be the truth? Did Boeing ignore the FAA in the B-737 & 747???

[Ranger One]

Heads up... FAA have issued an AD forbiding extended dry operation of center tank pumps on 737...

http://av-info.faa.gov/ad/PublishedADs/010824.html

[Flight Safety]

I wonder if this AD resulted from speculation coming from operational information about the 2 accident 733s, or if the information came from the NTSB/FAA actually running these fuel pumps dry on a bench and observing dry run failures in the pumps.

If the information is from actual dry pump tests then the pumps need to be redesigned, as anyone accidently leaving a fuel pump switch in the "on" position after the tank emptied could create a fuel tank explosion hazard.

I realize of course that the AD is an "interim" AD, and doesn't yet offer a terminating action.

[Burger Thing]

In our company (732-fleet) a new procedure has been introduced. Now air cond. ground operation when the center tank has less than 1500lbs. of fuel. Seems that the fuel in the center tank has a cooling effect for packs... We are mostly flying short sectors (center tank empty) in regions with temperature above 30 degrees of C and an external ground air con system is not available (no money...) Happy sweating !

[Canuck_AV8R]

Ranger:

I hate to rain on your parade but the centre tank pumps on a B737 (at least on the -200 that I fly)are not actually in the centre tank. They are housed in what Boeing calls an "igloo" in the respective main tank.

The reason for not running these pumps dry is that they are lubricated and cooled by the fuel running through them. When the centre tank is empty this cooling fuel is no longer available. Why would you want to run fuel pumps in an empty tank anyway it is a waste of time. And besides those Master Caution Fuel lights are a pain in the ass to have to keep cancelling.

Cheers

http://indigo.ie/~owenc/starwars/images/pint1.gif

[Burger Thing]

I think that it is a combination of problems, like in so many cases. In high ambient temperatures the air con packs are getting hot and causing with their increasing temperature a vaporization of remaining fuel in the center tank, which becomes an explosive mixture. This mixture coulp probably be ignited by dry run center fuel pumps. The cause is according to the FAA statement a 'metal to metal' contact, causing sparks. It doesn't probably really matter, if the center pumps has been cooled or not, therefore the LOCATION of those pumps is not the main problem here.