China Airlines B737 Fire at Okinawa
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W Weasel,
Jet-A, even when dumped into an existing fire, doesn't explode. It catches fire in an extremely spectacular manner, but without the destructive pressure wave that is part of the definition of an explosion.
A "true" explosion would have blown part of the aircraft apart, and the photos show that didn't happen.
Not always true, but a good description of what happens in fuel tank explosions: fuel vapor and air (hence oxygen) are premixed.
Jet-A, even when dumped into an existing fire, doesn't explode. It catches fire in an extremely spectacular manner, but without the destructive pressure wave that is part of the definition of an explosion.
A "true" explosion would have blown part of the aircraft apart, and the photos show that didn't happen.
Explosion : A very rapid combustion of a substance using its own oxygen supply. Initiated by ignition.
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FAA Orders Wing Inspections For New 737s
FAA Orders Wing Inspections For New 737s
Taken from CBSNEWS
WASHINGTON, Aug. 28, 2007
--------------------------------------------------------------------------------
A fuel leak through that hole likely caused the fire on the China Airlines Boeing 737-800, said Kazushige Daiki, chief investigator at Japan's Aircraft and Railway Accidents Investigation Commission. (AP Photo/Kyodo News)
Slats slide out the front edge of the main wings during takeoff and landing to stabilize the aircraft, along with flaps that come out of the wings' rear edge
Federal regulators ordered inspections of the wing slats on all newer Boeing 737 jetliners based on findings about the fire that destroyed a China Airlines 737 in Japan last week.
The orders apply to the owners and operators of 783 U.S. airplanes but will likely be imposed by other countries on the entire worldwide fleet of 2,287 newer 737s, Federal Aviation Administration spokesman Les Dorr said Monday.
Dorr said the move was prompted by the fire in Japan and one other incident.
The FAA's emergency airworthiness directive, issued Saturday, applies to all 737-600, -700, -800, -900 and -900ER series planes, the first of which entered service in January 1998 with Southwest Airlines, which flies only 737s. In the United States, the planes also are used by Alaska, American, Continental, Delta and other carriers.
The airlines have 24 days to conduct detailed inspections to confirm
that the movable slat system on the wings, which gives the plane lift, is installed properly, CBS News correspondent Nancy Cordes reported.
Slats slide out the front edge of the main wings during takeoff and landing to stabilize the aircraft, along with flaps that come out of the wings' rear edge.
Last Thursday, investigators in Japan found that a bolt from a right wing slat had pierced the fuel tank of the Taiwanese jetliner that caught fire after landing on the Japanese resort island of Okinawa. All 165 people aboard evacuated safely seconds before the plane exploded.
A fuel leak through that hole likely caused the fire on the China Airlines Boeing 737-800, said Kazushige Daiki, chief investigator at Japan's Aircraft and Railway Accidents Investigation Commission.
The FAA ordered a detailed inspection within 24 days to be sure that the downstop assembly, which limits how far the slats can emerge from the wing, is installed properly and repaired if needed. It also ordered that the nut and bolt that hold the assembly in place be tightened to specifications. And it ordered this process be repeated at least every 3,000 takeoff and landing cycles.
The airlines are going to try to do the inspections during routine maintenance checks, Cordes reported.
The FAA estimated the total cost for the U.S. fleet at $62,640.
The FAA order said that loose parts from one 737-800 downstop assembly had punctured the slat housing, which caused a fuel leak and fire that destroyed the plane - a clear reference to the China Airlines fire, although the company was not mentioned by name.
In the other case, a nut fell off the assembly and was pushed through the housing wall when the slats were retracted, the FAA said. Later, the operator found fuel leaking from the slat housing.
Following Thursday's findings, Japan's Transport Ministry ordered three Japanese airlines that own Boeing 737-800s to inspect the leading edge slats on the main wings to ensure bolts were in place before their first flight took off Friday morning, said ministry spokesman Yusuke Asakura.
Vicki Ray, a spokeswoman for Boeing Co. said the aircraft maker had received four reports of the nut coming loose from the downstop assembly and had issued a service letter to all operators of the newer model 737s in December 2005 telling them to check to be sure the nut was properly tightened. The service letter was updated several times since, most recently in July 2007, Ray said.
Taken from CBSNEWS
WASHINGTON, Aug. 28, 2007
--------------------------------------------------------------------------------
A fuel leak through that hole likely caused the fire on the China Airlines Boeing 737-800, said Kazushige Daiki, chief investigator at Japan's Aircraft and Railway Accidents Investigation Commission. (AP Photo/Kyodo News)
Slats slide out the front edge of the main wings during takeoff and landing to stabilize the aircraft, along with flaps that come out of the wings' rear edge
Federal regulators ordered inspections of the wing slats on all newer Boeing 737 jetliners based on findings about the fire that destroyed a China Airlines 737 in Japan last week.
The orders apply to the owners and operators of 783 U.S. airplanes but will likely be imposed by other countries on the entire worldwide fleet of 2,287 newer 737s, Federal Aviation Administration spokesman Les Dorr said Monday.
Dorr said the move was prompted by the fire in Japan and one other incident.
The FAA's emergency airworthiness directive, issued Saturday, applies to all 737-600, -700, -800, -900 and -900ER series planes, the first of which entered service in January 1998 with Southwest Airlines, which flies only 737s. In the United States, the planes also are used by Alaska, American, Continental, Delta and other carriers.
The airlines have 24 days to conduct detailed inspections to confirm
that the movable slat system on the wings, which gives the plane lift, is installed properly, CBS News correspondent Nancy Cordes reported.
Slats slide out the front edge of the main wings during takeoff and landing to stabilize the aircraft, along with flaps that come out of the wings' rear edge.
Last Thursday, investigators in Japan found that a bolt from a right wing slat had pierced the fuel tank of the Taiwanese jetliner that caught fire after landing on the Japanese resort island of Okinawa. All 165 people aboard evacuated safely seconds before the plane exploded.
A fuel leak through that hole likely caused the fire on the China Airlines Boeing 737-800, said Kazushige Daiki, chief investigator at Japan's Aircraft and Railway Accidents Investigation Commission.
The FAA ordered a detailed inspection within 24 days to be sure that the downstop assembly, which limits how far the slats can emerge from the wing, is installed properly and repaired if needed. It also ordered that the nut and bolt that hold the assembly in place be tightened to specifications. And it ordered this process be repeated at least every 3,000 takeoff and landing cycles.
The airlines are going to try to do the inspections during routine maintenance checks, Cordes reported.
The FAA estimated the total cost for the U.S. fleet at $62,640.
The FAA order said that loose parts from one 737-800 downstop assembly had punctured the slat housing, which caused a fuel leak and fire that destroyed the plane - a clear reference to the China Airlines fire, although the company was not mentioned by name.
In the other case, a nut fell off the assembly and was pushed through the housing wall when the slats were retracted, the FAA said. Later, the operator found fuel leaking from the slat housing.
Following Thursday's findings, Japan's Transport Ministry ordered three Japanese airlines that own Boeing 737-800s to inspect the leading edge slats on the main wings to ensure bolts were in place before their first flight took off Friday morning, said ministry spokesman Yusuke Asakura.
Vicki Ray, a spokeswoman for Boeing Co. said the aircraft maker had received four reports of the nut coming loose from the downstop assembly and had issued a service letter to all operators of the newer model 737s in December 2005 telling them to check to be sure the nut was properly tightened. The service letter was updated several times since, most recently in July 2007, Ray said.
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I am of course no expert on what constitutes an "explosion" but it does seem to me on pure visual observation of the videos of this event that the fireball was created when the undercarriage tyres, or at least their fuseable plugs, burst due to the heat. Presumably these very high pressure containers represent a huge amount of compressed air that, when released, inevitably results in significant disruption of a pool of burning kerosene that lies all around them. Is not this in itself enough to produce the observed "explosion"?
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nitrogen is the proper gas to be used in airliner tires or tyres.
and as such, the nitrogen shouldn't have contributed to the flames per se...I still think that the center tank vapors, could have been cooked off by the external fire possibly causing an explosion...the largest one visible prior to the major foaming of the plane.
and as such, the nitrogen shouldn't have contributed to the flames per se...I still think that the center tank vapors, could have been cooked off by the external fire possibly causing an explosion...the largest one visible prior to the major foaming of the plane.
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Originally Posted by Synthetic
Are the tyres not filled with nitrogen?
Originally Posted by Ranger 1
Yes, Nitrogen is used to inflate the tyres.
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Whether it's nitrogen or air makes no difference to the fact that it is a heck of a lot of compressed gas expanding rather suddenly in a pool of burning kerosene - it's still going to throw a lot of flammable mist around and create the fireball.
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Seloco,
We're thinking along the same lines, it seems.
But, looking at the video again, just when the fire appliances arrive, I have the impression by that time the fire was fed by far more than the original pool from the original leak. By that time the underwing structure would have burned through, fuel tank access panels would have been blown out, and far more fuel would be pouring into the fire.
We're thinking along the same lines, it seems.
But, looking at the video again, just when the fire appliances arrive, I have the impression by that time the fire was fed by far more than the original pool from the original leak. By that time the underwing structure would have burned through, fuel tank access panels would have been blown out, and far more fuel would be pouring into the fire.
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It involves an apparent maintenance error (my bold) and evacuation procedures.
All of which suggests a design deficiency rather than a pure "maintenance error. From the actual content of the two ADs and the relevant Boeing Service Letter, there may also be a 'Human Factors' element, concerning assembly of the parts.
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Re the fire/explosion. Back to basics. There are 3 requirements needed to start a fire:
Fuel
An oxidant
A source of ignition
Jet fuel does NOT burn in its liquid form at normal temps; it is the vapour that burns. Here things get more complex. The vapour will only ignite if it is present in quantities between the LEL (Lower Explosive Limit) and the UEL (Upper Explosive Limit). IE, if the mixture is too lean it won’t burn; if it is too rich it won’t burn.
Looking at the video, what appears to have happened is that a small vapour cloud found a source of ignition at the time it was in a concentration between the LEL and UEL. It may well by that the gas (N2?) from the tyres helped ‘atomize’ the fuel. The N2 then being displaced by air containing O2. The ignition source is open to conjecture.
Same principle is used in FAE (Fuel Air Explosives).
Fuel
An oxidant
A source of ignition
Jet fuel does NOT burn in its liquid form at normal temps; it is the vapour that burns. Here things get more complex. The vapour will only ignite if it is present in quantities between the LEL (Lower Explosive Limit) and the UEL (Upper Explosive Limit). IE, if the mixture is too lean it won’t burn; if it is too rich it won’t burn.
Looking at the video, what appears to have happened is that a small vapour cloud found a source of ignition at the time it was in a concentration between the LEL and UEL. It may well by that the gas (N2?) from the tyres helped ‘atomize’ the fuel. The N2 then being displaced by air containing O2. The ignition source is open to conjecture.
Same principle is used in FAE (Fuel Air Explosives).
The Reverend
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Why would the tyres burst? By all accounts it was a normal landing.They most probably burst when enveloped by the fire but it was not the ignition point.
All of which suggests a design deficiency rather than a pure "maintenance error.
Typically those two words imply a deficiency against a specified cause-effect standard. IMO this has not been established in this event. I prefer to look upon it only as a design improvement to make up for a maintenance deficiency
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HotDog wrote: Why would the tyres burst? By all accounts it was a normal landing.They most probably burst when enveloped by the fire but it was not the ignition point.
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This might be deemed a "human error - maintenance" probable cause, aggravated by the hardware design being difficult or impossible to inspect once in place. (Read: "Murphy's Law"...)
Such design characteristics are not at all unusual in aircraft (or any other machinery), and demand a skill and awareness level of technicians to prevent this sort of accident.
It's generally accepted today that such traps should be "designed out" of new aircraft. I'm not sure how much the NG 738 resembles the 732 (or 722, or ...) in this regard, but I doubt the feature is unique to the NG. In that case Boeing has built MANY thousands of aircraft with a similar "trap". It may be quite ironic that the tank rupture occurred on a low-time machine.
Such design characteristics are not at all unusual in aircraft (or any other machinery), and demand a skill and awareness level of technicians to prevent this sort of accident.
It's generally accepted today that such traps should be "designed out" of new aircraft. I'm not sure how much the NG 738 resembles the 732 (or 722, or ...) in this regard, but I doubt the feature is unique to the NG. In that case Boeing has built MANY thousands of aircraft with a similar "trap". It may be quite ironic that the tank rupture occurred on a low-time machine.
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I prefer to look upon it only as a design improvement to make up for a maintenance deficiency
In this instance we appear to have a significant number of cases of incorrectly assembled parts. In some cases - including the accident aircraft itself - on L.E. Slat systems that had not been disturbed since manufacture. Thus it is not a "maintenance" matter per se, but also includes production assembly - it seems that the correct way to assemble the parts is not clear and unambiguous. My own favourite example is the Air /Ground switch actuator assembly on the B707. It was such a simple mechanism that everyone just 'knew' how to disconnect it to simulate "Air" and put it back to "Ground" afterwards: nevertheless, one seldom found one that was correctly assembled.
The instinctive way is not always the right way and the correction is to design out the human factor.
Barit:
I'm glad you said this MIGHT be deemed a human error......aggravated by hardware design, because you are misinformed. There is very considerable science applied to the reliability of aircraft and all their components by people much smarter than I am.
Since at least about 1970, each and every component and assembly in an aircraft undergoes FMEA - Failure Mode Effects Analysis, which is performed by a Committee of Professionals (Engineers, etc.) who use a highly structured decision tree to review the way a part has been designed, its modes of failure and the consequences of failure and how it is to be maintained.
Such traps as you mentioned have existed ( Such as the Dunlop aviation manual for the Viscount cabin supercharger on the accessory pack for the RR Dart - the assembly order of thrust washers was ambiguous, resulting in an in flight fire that killed about 30 people) but these are generally caught and designed out of the aircraft by FMEA since at least 1970. Clearly some design issues will slip through, but its not from lack of trying.
Thats why Boeing and Airbus have service representatives almost everywhere, and anything that starts cropping up is relayed to Seattle or Toulouse(?) where it becomes the subject of discussion and action.
For the record, maintenance protocols for components relate to the severity of failure and the ease of inspection to determine the components condition.
This results in components being classified:
"Hard Time" - set limits on number of hours/cycles/stress history/ etc, which is what you do if there is no way you can gauge the condition of the item by simple inspection - for example disks.
"Condition Monitored" - you inspect the part at set intervals and if its within limits, thats OK. e.g. blades. flap tracks etc. I assume the end stop will be disassembled and inspected in the process of overhauling the LE slat.
"On Condition" - when it breaks, fix it, and not before. e.g seat jacks.
As for a "design defect" causing this fire, I guess its possible, but Boeing would have gone to considerable lengths to ensure that this assembly cannot be put together the wrong way and assumes an average level of skill from the engineers maintaining the aircraft.
Translation: If your car manual says "Torque wheel nuts to forty foot pounds" and you only torque to twenty, and the wheel subsequently falls off your car, that isn't a design defect at all. In fact the design is perfect and is operating exactly as predicted.
(runs for foxhole)
This might be deemed a "human error - maintenance" probable cause, aggravated by the hardware design being difficult or impossible to inspect once in place. (Read: "Murphy's Law"...)
Such design characteristics are not at all unusual in aircraft (or any other machinery), and demand a skill and awareness level of technicians to prevent this sort of accident.
It's generally accepted today that such traps should be "designed out" of new aircraft. I'm not sure how much the NG 738 resembles the 732 (or 722, or ...) in this regard, but I doubt the feature is unique to the NG. In that case Boeing has built MANY thousands of aircraft with a similar "trap". It may be quite ironic that the tank rupture occurred on a low-time machine.
Such design characteristics are not at all unusual in aircraft (or any other machinery), and demand a skill and awareness level of technicians to prevent this sort of accident.
It's generally accepted today that such traps should be "designed out" of new aircraft. I'm not sure how much the NG 738 resembles the 732 (or 722, or ...) in this regard, but I doubt the feature is unique to the NG. In that case Boeing has built MANY thousands of aircraft with a similar "trap". It may be quite ironic that the tank rupture occurred on a low-time machine.
Since at least about 1970, each and every component and assembly in an aircraft undergoes FMEA - Failure Mode Effects Analysis, which is performed by a Committee of Professionals (Engineers, etc.) who use a highly structured decision tree to review the way a part has been designed, its modes of failure and the consequences of failure and how it is to be maintained.
Such traps as you mentioned have existed ( Such as the Dunlop aviation manual for the Viscount cabin supercharger on the accessory pack for the RR Dart - the assembly order of thrust washers was ambiguous, resulting in an in flight fire that killed about 30 people) but these are generally caught and designed out of the aircraft by FMEA since at least 1970. Clearly some design issues will slip through, but its not from lack of trying.
Thats why Boeing and Airbus have service representatives almost everywhere, and anything that starts cropping up is relayed to Seattle or Toulouse(?) where it becomes the subject of discussion and action.
For the record, maintenance protocols for components relate to the severity of failure and the ease of inspection to determine the components condition.
This results in components being classified:
"Hard Time" - set limits on number of hours/cycles/stress history/ etc, which is what you do if there is no way you can gauge the condition of the item by simple inspection - for example disks.
"Condition Monitored" - you inspect the part at set intervals and if its within limits, thats OK. e.g. blades. flap tracks etc. I assume the end stop will be disassembled and inspected in the process of overhauling the LE slat.
"On Condition" - when it breaks, fix it, and not before. e.g seat jacks.
As for a "design defect" causing this fire, I guess its possible, but Boeing would have gone to considerable lengths to ensure that this assembly cannot be put together the wrong way and assumes an average level of skill from the engineers maintaining the aircraft.
Translation: If your car manual says "Torque wheel nuts to forty foot pounds" and you only torque to twenty, and the wheel subsequently falls off your car, that isn't a design defect at all. In fact the design is perfect and is operating exactly as predicted.
(runs for foxhole)
Sunfish
I doubt that Boeing assumed a level of "catastrophe" for this error in their FMEA and under what FAR would they perform this type of analysis for such an error (after all it doesn't prohibit safe light does it?
I doubt that Boeing assumed a level of "catastrophe" for this error in their FMEA and under what FAR would they perform this type of analysis for such an error (after all it doesn't prohibit safe light does it?
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assumes an average level of skill from the engineers maintaining the aircraft.
The accident aircraft was too low time to have had any maintenance work done in this area. Which points to it being assembled incorrectly during production. Which in turn implies some ambiguity in how to correctly assemble the components. Which is a Human Factors issue.
I could bore you to death for hours talking about all the poor maintainability that every aircraft I have ever worked on had designed into it. A friend and former colleague of mine works for Airbus "ensuring that what the designers have designed can actually be manufactured" - his words.