Twa 800

[nick charles]

ARAP E-Mail on Tank Explosions

To whom it may concern,

At 1:00pmET today, the Discovery Channel presented its TWA800 "documentary". As a manufacturer of UL Listed steel fuel tanks, I was disturbed by the presentation of a "scientific test" which demonstrated that a Boeing 737 fuel tank under "similar conditions" would indeed explode if a spark were introduced to the tank. I am therefore compelled to write in the hope that someone with a vested interest might read this.

I sense serious defects with the test as presented. As a manufacturer of steel fuel tanks for both fuel oil and gasoline use, there are several basic axioms which guide our designs.* One basic tenet is that a properly designed and vented fuel tank will not explode, even when engulfed in fire. The issue with a fuel tank is not explosion-- it is rupture from overpressure from gases produced by boiling liquid. Provided that the tank is vented, it will not rupture. We don't worry about explosion as much as tank rupture from overpressure or tank structural failure from heat. Most important, however, is that a fuel tank fully engulfed will not explode because there is no oxygen in the tank.

All of the "air" has been displaced by heavier-than-air fuel vapors. Remember that these tanks are vented-- these are not pressure vessels. So the residual fuel that would always be present in the tank would give-off vapors which displace the air out the vent. The Boeing 747 fuel tank in question had not been emptied. Presumably it had been quiescent on the ground for many hours prior to flight. The fuel tank should therefore have been fully saturated in fuel such that all "air" had been displaced. Furthermore, as the aircraft climbed, and pressure dropped, the tank would have further evacuated-- fresh air would not have been drawn into the vented tank until the aircraft descended. As air pressure dropped, so would the boiling point, resulting in a greater concentration of vapors and displacement of oxygen. Therefore, a spark or even an open flame could not have ignited the vapors.

Perhaps this explains why aircraft fuel tanks are not exploding all the time-- and car fuel tanks as well. In fact, TWA800 is the only aviation case I have knowledge of and I am an interested person who follows these things (I am a private pilot with a life-long aviation passion).

The Discovery Channel presentation is defective:
1. The test tank was freshly filled and immediately tested, not allowing time for the atmosphere within the tank to saturate with vapors as would have been the case with the TWA800 aircraft.
2. The test tank had air circulation fans installed within, which would have both inhibited evacuation of air and introduced fuel droplets into the air. The 747 had no such mixing fans.
3. The test tank was tested at atmospheric pressure. The TWA800 event occurred at 15,000 feet or so, where pressure is greatly reduced.
4. The test tank was artificially heated by a salamander perhaps producing spot overheating. The TWA tank would have been both at uniform temperature and would have cooled substantially during the climb.
Furthermore, the flash point of Jet-A is well above 100F. The test was performed at approx 125F, presumably below the flash point of Jet-A. A flammable liquid can only ignite in free air when the flash point is exceeded.

Artificially introduced droplets were probably introduced in the test. In fact, the test appears to be so defective as to be contrived such that the test tank was indeed a "bomb" producing desired results.

I am disturbed that this is presented to the gullible public as fact and the final word. I believe that the facts of metallic tank construction weigh strongly against the "results of the scientific test" presented on Discovery. Those of us who manufacture steel fuel tanks know this.

I have no political ax to grind and am not a conspiracy nut. However, as an engineer, a pilot, a person of knowledge and a manufacturer of fuel tanks, I have severe doubts that the TWA800 tank exploded from an internally introduced spark. The reasons presented above substantiate those doubts.

I hope that this letter will help advance your search for the truth.

President
Simplex, Inc.

[bubbers44]

TWA 800, in my opinion, was investigated from what they wanted the cause to be backwards to what could have caused it to happen that way. They decided the center tank exploded causing the disaster. Anything saying it wasn't a fault in the center fuel tank wasn't pursued seriously. Just my opinion.

[expatpilot4life]

Everyone knows it was a missle.

[PBL]

nick charles,

there is extensive investigation, including reports from the American Chemical Society, in the TWA800 docket on the NTSB WWW site.

I also wrote a paper on the energy required for ignition, which you can find on my WWW site (EMI, TWA 800 and Swissair 111).

This is not the only documented incident of CWTs exploding on Boeing airframes. (I am using the word "explosion" here to mean a rapid burn, with significant overpressure, after ignition.) Those who favor some other theory have to explain how their theory accounts for those other instances also. (In the case of our missile-theory advocates, it most obviously does not account for those other instances.)

The NTSB, and the American Chemical Society, believe that it is possible to ignite vapors in a CWT with a result similar to that in TWA 800. This contradicts your suggestion (as I understand it) that you don't see how it is possible, so perhaps you should check out the docket materials to see where either they fail or you fail.

PBL

[lomapaseo]

With a center fuel tank you don'y really have to blow out the four sides to cause a serious problem with the aircraft. TWA800 proved this. The center tank is an integral structural body of the arcraft and like a wing if you take out a spar or two you are going to have a serious cascading problem.

[Captain Sensible]

"Perhaps this explains why aircraft fuel tanks are not exploding all the time-- and car fuel tanks as well."
No, not all the time, but I know of at least 2 C130's whose wings have blown up due to defective booster pumps arcing across a defective phase when being switched off/on.
And as for conspiracy theories, well, we all try to keep an open mind, but for those of us flying 747's in recent years, the raft of bulletins, changes to AFM's, drills, QRH's, all to ensure the integrity of the Centre Wing Fuel Tank by making sure the respective fuel pumps are covered in all conditions, all to make sure we don't get downed by a missile???!!!
Sorry, sarcasm and all that, but my meaning's clear.

[Casper]

Oh well, at least I tried!

[barit1]

But then -
What explains the PR 737 ground explosion in 1990 (http://aviation-safety.net/database/record.php?id=19900511-1)that preceded TW800? Wasn't it unequivocably the center tank?

And don't forget - early B-47's used to inexplicably blow up in the landing pattern after long training missions. The problem went away after changing out the DC fuel pumps (w/commutators) for AC pumps. (This from an ex-SAC pilot who lost a colleague or two in the 50s)

[Pugilistic Animus]

Well, my 'conspiracy theory agrees 100% with the NTSB...

However, as an aside my uncle a retired Naval officer, informed me that during the time of flight 800 the Navy was testing a very high powered radar antenna {not entirely sure exactly what} installation.

He then informed me that they frequently 'lock on to civil airliners' for practice drills and calibration of such equipment [and just look around that area on sectionals and you know they do 'something secret' around that airspace] perhaps that was the initial trigger of the arcing condition perhaps an overvoltage/surge was the final dagger in the heart of flt 800

so while I agree that the ingredients for disater existed I do not rule out that there was maybe so "extra help" getting it started

Now, my uncle is very sane and knowledgeable about Naval operations [having served on many many ships in his 20 years of service] ...and he didn't say that that was definitely the cause but........

[con-pilot]

For now I am still going along with the official NTSB findings. However, I would consider a different solution, if it based on actual facts, not Internet unprovable theories.

[PBL]

However, as an aside my uncle a retired Naval officer, informed me that during the time of flight 800 the Navy was testing a very high powered radar antenna {not entirely sure exactly what} installation.

He then informed me that they frequently 'lock on to civil airliners' for practice drills and calibration of such equipment [and just look around that area on sectionals and you know they do 'something secret' around that airspace] perhaps that was the initial trigger of the arcing condition perhaps an overvoltage/surge was the final dagger in the heart of flt 800

No. This is the hypothesis that Elaine Scarry proposed in the NYRB. It has been definitively discredited by NASA and myself and Willie Schepper. Please read the NASA report in the docket, and read our paper.

PBL

[BelArgUSA]

Attn. Nick /
xxx
Ex PanAm 747 pilot, then based JFK, I had many friends flying 747s with TWA. We often compared our procedures and discussed our airplanes and their differences, as I was often instructing in classrooms or simulators at the PA Academy in Miami... I now fly 747s in Argentina, manager pilot training, and when TW 800 crashed, no need to tell you, we were in contact about the facts and... theories.
xxx
No need to say, all ex-PanAm flight crews, like myself, immediately thought about "foul play", a bomb, a missile... after all, PanAm, as well as TWA, were considered by terrorists as the perfect targets representing the USA when overseas. It took me a long time, until the final report by the NTSB, to believe that TW 800 went down with a CWT explosion... Remember Lockerbie.
xxx
That the explosion occured at some 13,500 feet in the climb, is no surprise. TW 800 was dispatched from JFK to CDG, with wing tanks and reserves near full, but no extra fuel was required nor loaded in the CWT. The plane had landed in JFK arriving from Europe, with the usual residual fuel remaining in the CWT. And yes, that fuel was warm, because of the A/C packs used on the ground at JFK. How warm...?
xxx
An AFM 747 limitation is "maximum fuel temperature" for Jet A or Jet A-1 to be 54.5ºC in the tanks. The fuel is generally warmer in the CWT because of the A/C packs. You said that fuel cools off rather fast... well, it cools off (not so fast, but it does cool) in the wing tanks, not much in the CWT...
xxx
There is no "CWT fuel temperature" that we can read in the 747. We can read fuel tank temperature for tank nº1, or for each separate engine feed. here in Argentina, if the fuel gets very cold on our very long flights (minimum temperature for Jet A or A-1 limit is 37ºC in our limitations), we sometimes keep 2 or 3,000 kilos of fuel in the CWT until needed to be used to warmup the engine feed lines, if needed. I know that after 10 hrs in cruise, that fuel remains rather warm in the CWT, maybe 10 or 20ºC warmer than wing tanks.
xxx
However uneducated we pilots and flight engineers are in the 747, it is very likely that the CWT exploded when the F/E on the flight operated the "scavenge pump". Why...? With PanAm, as well as with TWA, our F/E's SOP performed after passing 10,000 feet in the climb, was to activate the scavenge pump to "suck the last drops" of an "empty" CWT and transfer that fuel into the nº2 main tank. Many of us believe that this, triggered the explosion, probably with a short in that electrical wiring or motor. So, 13,500 feet makes sense...
xxx
I know that UAL F/Es used to do same SOP, but at 18,000 feet in climb... and here in Argentina, we did that scavenge, to complete our "after takeoff checklist" at flap retraction at some 3 to 5,000 feet if our CWT was empty. No need to tell you that we no longer do such a procedure... If a few liters of fuel remain in the CWT, well, who cares...? -
xxx
A few years ago, smartass as I am, with my Zippo lighter, and filled it with a few drops of Jet A-1. I could never use it again, and had to buy a new one. Jet fuel is extremely difficult to light-up. At PanAm, we flew many military MAC flights contracts, and the Air Force often delivered Jet B fuel (JP-4). For that fuel, we had a lot of limitations, such as maximum pressure for fueling, and maximum temperature reduced to 43ºC...
xxx
Thank you for your input about steel tanks, it is appreciated. However good the "Discovery Channel" is, obviously it is for the general public.
:)
Happy contrails

[robertsgt40]

It should be clear to the most myopic that there is something fishy in the whole "tank" issue. With eye witnesses seeing two trails heading towards the craft(Coast Guard officer in a helicopter) to investigations of rocket propellant on seats. Not to mention the idea that a jet can continue to rise after a catastophic explosion. NTSB is the same guys that told us that UA 93 nosed over into the ground in Pa. when parts and pieces were found miles away. The fuel tank is easier to sell and eliminates law suits against a friendly fire situation.

[con-pilot]

He's from Texas, ignore him. :p

[lomapaseo]

Ignore him yes, but I do expect the mods to clean up the extraneously bolded font

[Dream Land]

Not a conspiracy person myself, but after reading about the investigation it seems very fishy, thanks BelArg for your experienced perspective.

[Casper]

Good thread. But can anyone explain why the FBI still (after 10 years) lists this investigation as "pending inactive," the one and only category that permits them to withold evidence? If it was, in fact, a CWT explosion and NO crime, why is the FBI STILL even involved?

Also, why does the FBI STILL withold the pathological evidence about foreign objects removed from the bodies of the victims? Even the official pathologist has not been informed!

[IGh]

Just above, Casper posed a question and a comment:

"... why does the FBI STILL withold the pathological evidence about foreign objects removed from the bodies of the victims? Even the official pathologist has not been informed!"

Nobody doubted Dr. Shanahan's daily briefings regarding his examinations of the victims, nor any "objects removed from the bodies". He was honest and open regarding such medical evidence [AAR also cites the Medical Forensic Group Chairman’s Factual Report, dated October 17, 1997].

The AAR reviews this subject of medical exams on pg 85:

= = = \/ = = = EXCERPT from AAR 00-03 = = = \/ = = =

Exhaustive analysis of all available medical data on the victims of TWA Flight 800 by an experienced team of forensic pathologists, biomechanicists and criminal investigators failed to find any evidence that any victim was directly exposed to a bomb blast or missile warhead detonation. This finding makes it highly unlikely that a localized explosion occurred within the passenger cabin of TWA Flight 800.

-- All injuries found in the victims were consistent with severe in-flight break up and subsequent water impact.

-- Injury and burn patterns to the victims as well as some body locations suggest that there was a severe break up of the passenger cabin early in the crash sequence.

-- Fire propagated ...cabin zone located above the CWT ... after most occupants [of this section] had been ejected. The small number of passengers with burn injuries exhibited only superficial burns consistent with exposure to a flash flamefront.

= = = /\ = = = END EXCERPT from AAR pg 85 = = = /\ = = =

[nick charles]

Just two questions.

If it was a CWT explosion and no crime was involved, why are law suits under the FOI Act still required to obtain information? - more than ten years after the event

And why does the FBI still list the case as "pending inactive?"

[fesmokie]

When I was new on the panel on the classic, I did everything possible ( not on purpose) to blow up the CWT and nothing!! :} I don't really believe the tank theory. The missle theory seems more likely as there were so many attempts to cover up info by the government and there were also several reputable eye witness's.

[fire wall]

BelArgUSA and IGh, I too still fly the old girl. My understanding is that the scavenge pump is located in the LH body gr wheel well.... not in the tank. If this is the case then please explain how an ignition source could be generated by such.
Regards.

[polzin]

Did anyone besides me see a video shown on TV taken at a beach which showed a smokey trail upwards at the time TWA 800 was flying over?

[lomapaseo]

..there were also several reputable eye witness's.

all the reputable eye witness's were countermanded by equally reputable non-government investigators who in turn carried expert credentials at separating fact from fiction.

[PBL]

If it was a CWT explosion and no crime was involved, why are law suits under the FOI Act still required to obtain information? - more than ten years after the event


What an odd statement.

I have a very large folder full of information on the accident, known as the NTSB docket, which includes substantial reports by major scientific organisations on various aspects of fuel tank fires (flammability, ignition and so on). Indeed, there is so much there that one can publish alternative theories in the New York Review of Books which contradict some of the hard evidence in the docket and yet no one will notice.

Presumably the FBI wants to keep its data to itself because that is what the FBI does when it collects data on, inter alia, military activities.


And why does the FBI still list the case as "pending inactive?"

Good question for FBI watchers. Because they can't be bothered to reclassify it? Or because someone there is embarrassed that after so much fuss they found nothing and had to hand the investigation over to the NTSB and is still hoping there might be something there? Or because someone there is a conspiracy theorist?

I might as well ask a question that has been puzzling me. Since you say you are a manufacturer of such fuel tanks, how come you think ullage cannot ignite, despite reams of evidence to show that, and how, it can, and a preceding case to TWA 800 where it did? Would one really want to buy
a fuel tank from someone who apparently wants to contradict what the American Chemical Society, NASA and the NTSB consider to be the established physics and chemistry of a potential hazardous event with such a tank?
Or can you show where the ACS, NASA and NTSB have made mistakes? If so, please share.

PBL

[PBL]

Did anyone besides me see a video shown on TV taken at a beach which showed a smokey trail upwards at the time TWA 800 was flying over?

I think a former press secretary to President Kennedy made quite an ass of himself in public over such videos, if I remember rightly.

PBL

[PBL]

I don't really believe the tank theory

I take it you do not understand the physics and chemistry laid out in the docket? I think that is probably a prerequisite for having one's opinion considered seriously.

PBL

[Dream Land]

Something smells. :hmm:

[fesmokie]

Originally Posted by fesmokie
I don't really believe the tank theory
PBL Or can you show where the ACS, NASA and NTSB have made mistakes? If so, please share.
PBL...No I can't show you where they have made mistakes as I don't have the articles in front of me however...can you show me they have not made mistakes?:=

[Checkboard]

Makes you think - if the investigation result had determined a missile attack as the probable cause, how many people would be crying "Conspiracy! Boeing and FAA cover up centre tank fuel explosion!!" :hmm:

[IGh]

From Chkbd, just above: "... if the investigation result had determined a missile attack as the probable cause ... people would be crying 'Conspiracy! Boeing and FAA cover up centre tank fuel explosion!!'"

That's just what "accident" investigators were up against, from the very beginning. Metal wreckage was on the ocean floor -- and a Respected Pilot Gossip sent an email outlining the detailed missile scenario. That did it: the whole story was right there on this new thing called the "web". The missile scenario must be true, it was on the web (while the direct evidence was still on the ocean floor).

Much later the wreckage was recovered from the bottom of the ocean, and law enforcement agreed that there was no evidence of "detonation" anyplace on the wreckage. Everyone agreed that there had been a "deflagration" inside the near-empty center tank. On day two we had told the FBI about the sister-ship's inflight breakup over Madrid in May'76.

[20driver]

IGh - re the sister flight break up, May 76, can you provide some more details or links?
Thanks
20driver

[PBL]

PBL...No I can't show you where they have made mistakes as I don't have the articles in front of me however...can you show me they have not made mistakes

I don't have to. The opinion of someone who expresses it in public, but hasn't read any of the studies which are available for years on the WWW, is hardly worth the pixels it is printed in. Please do your homework; then we can engage in a discussion about the explanation and where it may be right or wrong.

PBL

[IGh]

Question from two slots above: "... the sister [-ship] ... break up, May 76, ... provide some more details ..."

The US Safety Board provided an NTSB-AAR-78-12, on web at
http://www.airdisaster.com/accrep/#1978


Iranian Air Force flt ULF48, 9May76 daylight 1430 GMT, B747-131 (cargo conversion) to McGuire from Tehran, inflight structural failure, inflight breakup, crashed near Madrid Spain.

Left wing separated at an altitude of 6000', in severe wx and TRW, and Electrical Storms. FDR inop at time of accident. You can read the CVR analysis on AAR pg 5+.

A/C purchased from TWA on 1Mar76 [along with a second B747 later returned to TWA (really never left Boeing-Wichita) suffering the later 17Jul96 accident], large cargo door installed at Boeing-Wichita. Left Wing showed no evidence of pre-failure damage, nor stress corrosion, nor fatigue. Left Wing had three separate span-wise failure locations.

Board examined three possible causes:
* possible internal over-pressure in fuel tank;
* possible turbulence loads; or
* possible dynamic loads from whorl of engine pylon.

Damage indicated explosion, possible P.C.:

-- first, ignition of fuel vapors in #1 fuel tank w/over-pressure.

-- 2nd, integrity of aft wing lost, reduced torsional strength; then oscillation (flutter) of wing and engine pylon, then compression fracture of upper structure of left wing.

Witnesses rept'd lightening strikes (but vent outlet Surge Tank Protection had NOT activated, suggesting that lightening didn't hit near vent). [Note, TWA had installed STP on various models.]

Report listed five lightening accidents (Constellation near Milan Italy, B707 near Elkton MD, USAF KC-135 near Madrid, KSC FL USAF F-4, Pacallpa Peru L-188) all attributed to Lightening Strike to a wing followed by explosion in same wing.

In this B747 case ignition at vent outlet was not found, prompting investigators to list other strike routing-ignition paths.

No final P.C., only hypotheses of Lightning or Turbulence.

Investigated by US-NTSB, NTSB-AAR-78-12.

Recall that only a few months later, the C141 inflight breakup over London -- records show investigators comparing notes re' Turb vs Lightning, in each case.

[20driver]

IGH - thanks for the link. Interesting read
Just to keep the conspiracy crowd happy, the TWA 800 jet spent some time in Iran as well. All part of the plan.
20driver

[polzin]

Boeing has to my knowledge admitted a design problem if it found it to be so. Admitily sometimes it took time, such as the 737 rudder problem. But that was a Boeing employee, as i remember, who figured it out.

At the time of the TWA 800 accident I think that Boeing was adament that the short in the pump, explosion in the center tank was false and a rush to judgement by especially the FBI.

Now my question. Did Boeing ever agree to the conclusion?
kp

[lomapaseo]

Boeing has to my knowledge admitted a design problem if it found it to be so. Admitily sometimes it took time, such as the 737 rudder problem. But that was a Boeing employee, as i remember, who figured it out.

At the time of the TWA 800 accident I think that Boeing was adament that the short in the pump, explosion in the center tank was false and a rush to judgement by especially the FBI.

Now my question. Did Boeing ever agree to the conclusion?
kp

Could you parse these statements and questions down to one subject at a time? I can't figure out if you are mixing multiple accidents together in a single thread relative to what Boeing's position was or what the findings of the investigations showed for which accident:confused:


And as in any accident investigation, if Boeing were to disagree they would have filed a formal disagreement in the record which ought to be searchable.

[polzin]

Lomopisso,

No I can't.

So did you search it?

Out of the wrong side of the bed this morning?

kp

[GlueBall]

10 year old Thai B737-4D7, c/n 25321, HS-TDC, empty center tank "exploded" at the jetway at BKK 03-03-2001. Apparently the CWT pump was left running in an empty tank.

One of the superlative CWT pump fail safe designs can be found in the old Douglas DC-8: The CWT pump is inside the No.2 Main Tank, always inmersed and cooled by its fuel. :ooh:

[cyrus15]

Let’s get back to basics:

1. How can a CWT explode in mid air only in that particular aircraft during normal flight, though B747 been in service since 1973. (Supposedly no act of sabotage involved in here).
2. At 13000 feet, air (oxygen) can’t enter the fuel tank due to low ambient pressure and even in empty or half / quarter tank full; the pressure is equalized as the altitude changes. So the possibility of air getting in is not there not to mention the existence of fuel vapor pressure that occupy the empty space seeking lower pressure area to escape well prevent any air to get in (this is during flight).
3. If the electrical device in the fuel tank is electrically shorted or overheated (incase of running dry) what is the possibility during flight to have fire or explosion in this condition? Where the needed oxygen should come from?
4. How fire extinguisher works?
5. The theory of fuel tank explosion in mid air has been talked about and discussed in a span of couple of days after the accident and before even the wreckage recovery started. Four years later in a televised conference, all agencies (NTSB, FBI, FAA etc.) Conclusion was “fuel tank explosion”.
6. Commercial jet engines operation principal are not the same as rockets or space shuttle engines so do the fuel used in both engines are not the same (no oxidizers in jet fuel and no after burner engine used in this case).
7. Did anybody examine the AD (Airworthiness Directive) issued after this accident? How extensive is the work to comply with it? Is there any major changes of fuel tank designs introduced? What other than visual inspection and wire harness change required?
8. Most fuel injected cars (gasoline) has pump in the fuel tank, it is DC powered type of pump, that didn’t cause any concerns of the DOT, NTSB and other regulatory agencies knowing that gasoline is more volatile than kerosene based jet fuel and still the same principal fuel tank designed used. Road Accidents are more likely to cause automobiles fire but not fuel tanks will be on fire by design flaw.

To sum it up:
· Commercial jet fuel tank (bladder or steel type if any) doesn’t explode in mid air. You need fuel, oxygen and source of ignition combined at the same time to have fire or explosion in any fuel tank.
· Fire extinguisher works under the principle of isolating air (oxygen) from the fire, that’s why magnesium fire is a problem because it can produce oxygen when it burn.
· Four years later and millions of dollars spent to tell the same wrong conclusion that started in a matter of days after the accident? Is it plausible?

What is the logic behind permitting manufacturer to have electrical equipments inside fuel tanks (submerged pump) knowing that it could serve as ignition source? Unless there is a strong reason to do so, something like law of physics.

(fuel + source of ignition or heat + no oxygen = No Fire)

[bsieker]

Let’s get back to basics:

Good idea. Let's call it "Science 101".

1. How can a CWT explode in mid air only in that particular aircraft during normal flight, though B747 been in service since 1973. (Supposedly no act of sabotage involved in here).

Probably because great care is taken to keep ignition sources away from fuel tanks. So only very rarely there will be one. The mode of ignition in this accident has never been identified definitively.

2. At 13000 feet, air (oxygen) can’t enter the fuel tank due to low ambient pressure and even in empty or half / quarter tank full; the pressure is equalized as the altitude changes. So the possibility of air getting in is not there not to mention the existence of fuel vapor pressure that occupy the empty space seeking lower pressure area to escape well prevent any air to get in (this is during flight).

Now let's see.

Tanks have vents.

Fluids (i. e. gases and liquids) stream from regions of higher pressure towards regions of lower pressure. What is the pressure inside and outside the tank?

If we go along with your premise that no air was in the tank to begin with (more on that later), the only thing inside the tank to create pressure is the fuel vapor pressure. The only value I have found is for JP-8 at 38 degrees Celsius: it is about 200Pa. Another document about Jet-A1 mentions "less than 10hPa", so, let's be generous and assume 1000Pa.

Ambient air pressure at 13,000ft is around 50,000Pa, i. e. 50 times the inside pressure.

To figure out which fluid will stream into which direction is left as an exercise to the reader.

3. If the electrical devices in the fuel tank are electrically shorted or overheated (incase of running dry) what’s the possibility during flight to have fire or explosion in this condition? Where the needed oxygen should come from?

Well, from the air, I guess. See above. The correct solution to the exercise above is: it will stream from the outside into the tank, because the pressure outside the tank is higher than inside. One of the characteristics of jet fuel is its very low vapor pressure.

An additional thought: Why do you think many modern jet airliners have tank interting systems, which feed nitrogen-enriched air into the tanks, to reduce the amount of oxygen, to reduce the chances of creating a flammable fuel/air mixture.

I also recommend actually reading the TWA800 accident report. The investigators did actually test fuel/air mixture ratios in actual fuel tanks in flight and found them to be in the flammable range. See section 1.16.5.1.1.1 of the report.

4. How fire extinguisher works?

Many different ways. Some (the most efficient, like Halon) are chemical inhibitors that bind free radicals, thus breaking the reaction chain. Others replace the air (oxygen) around the fuel to stop the reaction. Water (water vapor) and foam are common.

5. The theory of fuel tank explosion in mid air has been talked about and discussed in a span of couple of days after the accident and before even the wreckage recovery started. Four years later in a televised conference, all agencies (NTSB, FBI, FAA etc.) Conclusion was “fuel tank explosion”.

Interesting. A theory that is discussed early on can never be true?

6. Commercial jet engines operation principal are not the same as rockets or space shuttle engines so do the fuel used in both engines are not the same (no oxidizers in jet fuel and no after burner engine used).

True. Same for military jet aircraft. Btw. liquid rocket fuels do not contain oxidisers, either, those are separate. As a side note, the most powerful rocket to date (Saturn V) used kerosene as its primary-stage fuel.

8. Most fuel injected cars (gasoline) has pump in the fuel tank, it is DC powered type of pump, that didn’t cause any concerns of the DOT, NTSB and other regulatory agencies knowing that gasoline is more volatile than kerosene based jet fuel and still the same principal fuel tank designed used. Road Accidents are more likely to cause automobiles fire but not the fuel tank will be on fire by design flaw.

The fuel pump as such was not found to be the ignition souce. Secondly, car fuel pumps are usually not submerged in the tank, but somewhere down the line, which their electrical parts away from the fuel line.

magnesium fire is a problem because it can produce oxygen when it burn.

No. Magnesium fire does not create oxygen (where from?)

Magnesium fire is a problem because it continues burning under water, because, very simply put, oxygen binds stronger to magnesium than to hydrogen (in the water), so magnesium "uses" the oxygen in the water molecules to burn, thereby freeing hydrogen.

Divers use magnesium torches.

· Four years later and millions of dollars spent to tell the same wrong conclusion that started in a matter of days after the accident?

What's wrong with a few smart people having the right hunch from the beginning? Or with an extensive investigation to find out the real cause.

Is it plausible?

I think so.


Bernd

[cyrus15]

Hello everyone,

Attention: bsieker (Bernd)

Indeed, let’s call it Science 101


"Now let's see. Tanks have vents. Fluids (i.e. gases and liquids) stream from regions of higher pressure towards regions of lower pressure. What is the pressure inside and outside the tank?
If we go along with your premise that no air was in the tank to begin with (more on that later), the only thing inside the tank to create pressure is the fuel vapor pressure. The only value I have found is for JP-8 at 38 degrees Celsius: it is about 200Pa. Another document about Jet-A1 mentions "less than 10hPa", so, let's be generous and assume1000Pa.
Ambient air pressure at 13,000ft is around 50,000Pa, i. e. 50 times the inside pressure. To figure out which fluid will stream into which direction is left as an exercise to the reader."


I agree with your first paragraph.

The vapor pressure of JP-8 at 38 oC is correct but not in this case.

Here’s the deal: check out the MSDS link for JP-8
http://www.hess.com/ehs/msds/JP8_HOV_4088_clr.pdf

Under basic physical properties section 9 it says:

BOILING RANGE: 280 to 572 oF (140 to 300 oC)
VAPOR PRESSURE: 0.029 psia @ 100 oF (38 oC)
VAPOR DENSITY (air = 1): AP 4.5
SPECIFIC GRAVITY (H2O = 1): 0.75 - 0.80
PERCENT VOLATILES: 100 %
EVAPORATION RATE: Slow; varies with conditions
SOLUBILITY (H2O): Negligible

The vapor pressure is 0.029 psia, that is equivalent to 200 Pascal (Pa) you mentioned but that is in Absolute pressure reading (almost in vacuum condition). Meaning; you can’t mix absolute pressure and atmospheric pressure readings without the proper conversion.

To do so, we should get the vapor pressure at the corrected temperature added to the ambient pressure at also the corrected temperature and altitude to get the pressure inside the fuel tank at that altitude.

So, according to your figures (assuming it is temperature and altitude corrected) we should have 200Pa + 50000Pa to get the pressure inside the fuel tank at 13000 feet, that's why tank vent is needed to allow the 50000 Pa to get in the tank though in real life, the tank pressure is little higher than ambient pressure because of the vapor pressure, that’s the correct solution to the exercise.

In the issued AD (after the accident) one item calls for adding small fuel quantity in CWT and should be considered as part of zero weight of B747 (very much permanent additional weight) to prevent the in-tank pump from running dry and overheat.

more on absolute, gauge and ambient pressure (PSIA/PSIG) reading can be found in this link; http://www.iceweb.com.au/Technical/pressure_measurements_info_notes.htm


"The fuel pump as such was not found to be the ignition souce. Secondly, car fuel pumps are usually not submerged in the tank, but somewhere down the line, which their electrical parts away from the fuel line."


The first part of your paragraph is correct but not the second part, take a look at these websites:

See the picture of a typical automobile fuel pump housed in the tank at:
http://www.trustmymechanic.com/parts_gallery/fuel_sending_unit.htm

And here’s an article from popular mechanics December 1997 issue talking about replacing an in-tank pump.
http://www.popularmechanics.com/how_to_central/automotive/1272236.html

Volkswagen Fuel pump (read the description)
http://replacement.vdubpartsdirect.com/parts/vdubpartsdirect/wizard.jsp?year=1998 &make=VW&model=PAS--004&category=E&part=Fuel% 20Pump&returnurl=null&dp=true

1997 Saturn fuel pump
http://replacement.vdubpartsdirect.com/parts/vdubpartsdirect/wizard.jsp?year=1997 &make=SN&model=SCSE--002&category=E&part=Fuel% 20Pump&returnurl=null&dp=true

Old cars (imperial 1981-1983) pump repair
http://www.imperialclub.com/Repair/Fuel/pump.htm

Go to"The Fuel Pump" paragraph at this link
http://www.picotech.com/auto/tutorials/fuel-injection.htm

At the end it reads:
"Fuel passing across the fuel pump's armature is subjected to sparks and arcing; this sounds quite dangerous, but the absence of oxygen means that there will not be an explosion!

The majority of fuel pumps fitted to today's motor vehicles are fitted within the vehicle's petrol tank and are referred to as 'submerged' fuel pumps. The pump is invariably be located with the fuel sender unit and both units can sometimes be accessed through an inspection hole either in the boot floor or under the rear seat. Mounted vertically, the pump comprises an inner and outer gear assembly that is called the 'gerotor'. The combined assembly is secured in the tank using screws and sealed with a rubber gasket, or a bayonet-type locking ring. On some models, there are two fuel pumps, the submerged pump acting as a 'lift' pump to the external roller cell pump."

Also see the picture (Figure 1.2) in the same page.

"An additional thought: Why do you think many modern jetairliners have tank interting systems, which feed nitrogen-enriched air into the tanks, to reduce the amount of oxygen, to reduce the chances of creating a flammable fuel/air mixture."

Fuel Tank Inerting System is nothing new (since the 50’s); it is associated mostly with military aircrafts particularly when flying in combat zone. Up to now most modern jetliner including B747 do not have this system.

The FAA tested the system you mentioned back in the 70’s and didn’t make it mandatory because of the advantages vs. cost are not favorable, but recently, (after the accident) new developments brought back the possibility to incorporate this system in commercial wide body jetliners particularly the ones with center fuel tank. Meanwhile, we just wait for the final word from the FAA.

[bsieker]

cyrus15, thanks for the reply.

I stand corrected on the car fuel pumps, I appreciate the links.

Now back to relevant matters.

Here’s the deal: check out the MSDS link for JP-8
http://www.hess.com/ehs/msds/JP8_HOV_4088_clr.pdf

Yes, that is the document I was referring to.

The vapor pressure is 0.029 psia, that is equivalent to 200 Pascal (Pa) you mentioned but that is in Absolute pressure reading (almost in vacuum condition). Meaning; you can’t mix absolute pressure and atmospheric pressure readings without the proper conversion.

That is only partially correct. It is an absolute pressure if the gas is the only gas in the "atmosphere", but if there is another gas present, this value is also the partial pressure (http://en.wikipedia.org/wiki/Partial_pressure) of that substance in the gas mixture. That's how gases work.

To do so, we should get the vapor pressure at the corrected temperature added to the ambient pressure at also the corrected temperature and altitude to get the pressure inside the fuel tank at that altitude.

What would create the ambient pressure inside the tank, to which you add the vapor pressure?

This only applies under very specific conditions, namely that there was atmopheric pressure in the vessel to begin with, created by some other gas, then you add some JP-8. In that case you are correct, we have to add both pressures, and some portiion of the vapor/air mixture would be vented to equalise inside and outside pressure.

So, according to your figures (assuming it is temperature and altitude corrected) we should have 200Pa + 50000Pa to get the pressure inside the fuel tank at 13000 feet, that's why tank vent is needed to allow the 50000 Pa to get in the tank though in real life, the tank pressure is little higher than ambient pressure because of the vapor pressure, that’s the correct solution to the exercise.

So, what is creating the 50,000Pa inside the fuel tank, if not air? :ugh: (Hey, finally I also got to use that smiley! :) )

I guess it must be Phlogiston (http://en.wikipedia.org/wiki/Phlogiston_theory).



Bernd

[polzin]

This is a terrific discussion and I hate to admit maybe beyond my comprehension. But one thing still bothers me, the FBI didn't have time to do any of these tests or analyisis before they decided that it was a problem with the aircraft.
True? Or over the years have I forgotton the time line? Honestly don't know.
any comments....Thanks in advance.
kp

[PBL]

kp,

But one thing still bothers me, the FBI didn't have time to do any of these tests or analyisis before they decided that it was a problem with the aircraft.

Whether they had time or not, they didn't do it. The FBI were investigating a possible crime, not trying to work out the physics and chemistry of fuel tanks.

If you take a look at the docket, which is quite large, contained multiple-hundred-page reports by NASA and so on, you will find that most of that substantial amount of work by civil agencies (more than just the NTSB) on fuel tank flammability and ignition sources took place after the civilian agencies were allowed to start their investigation.

PBL

[cyrus15]

Ok, let’s take a look at an empty tank on ground; let’s say it is 3 x 3 x3 meter 27 cubic m in volume with vent. As it is, it is full of air at the same atmospheric pressure say 101320 Pa (14.7 psig) so we have inside and out side pressure of that tank is 14.7psi. We are going to consider the major factors (mostly the physical properties listed in the MSDS).

Say we fill it up with 3cubic meter JP-8, we should have 24 cubic meters empty, but it is still occupied by air at the same pressure on ground (101320 Pa standard atmospheric pressure) and the remaining 3 cubic meter of air has been displaced by the fuel volume.

Let’s take that tank up to 13000 feet (flying fuel tank….!) now we have 50000Pa atmospheric pressure at that height in the tank acting on the surface of the fuel as well as all surfaces, so the rest of the atmospheric pressure (101320 Pa) has gone through the vent to the atmosphere leaving 24 cubic meters of less dense air inside the tank (less oxygen less other gases in the air) plus whatever fuel fume that would escape till the pressure equalize.

Now we have an enclosure with 3 layers of fuel in a liquid form, fuel vapor (heavier than air) and the rest is thinner air at that pressure / altitude / temperature combination. Say at that altitude you opened the filling cap of that tank and you dropped a burning wood stick (source of fire) in the tank, you will burn the air / fuel vapor mixture only in the area where it is combustible (the upper area of the vapor layer and the lower area of the air layer) and the fire well die very quickly leaving hot exhaust with insignificant amount of pressure escaping to the atmosphere.

That combustion is extremely inefficient producing inherently low energy yield because of improper fuel air ratio and also equally important the amount of air available in the tank that can support a significant fire, let alone explosion.

If you take a cup half filled with gasoline and you light it up with a lighter you will have a “poof” like fire and it will die quickly (please don’t try this at home) why the fire will not continue burning? Because the combustible layer is crudely atomized with air in unsustainable fashion.

fuel pump (booster, transfer or scavenge pump) are submerged under the fuel, even when that tank is almost empty, it is still well under the fuel vapor layer where no oxygen reaching that part of the tank even on ground because the vapor density of the fuel is higher than air, it will stay at the lower area of the tank.

The vapor pressure plus the evaporating rate of the fuel in the tank will significantly increase in low atmospheric pressure condition at that altitude, in effect, it will increase the pressure inside the tank and push the air out in proportion to the volume it create. Add to this the fuel temperature effect where further more increases the pressure as it rise. So at this point we have even less air volume in the tank and more fuel vapor layer because of the high vapor density.

Another major factor to consider is fuel atomization. When we talk about combustion we are referring to mixing fuel and air in a ratio that can produce a desired amount of heat out of burning, in real life fuel tanks are not designed for this. That's why Nick Charles is disputing the documentary he have seen and asking why those guys having air circulation fans in the tank that help atomizing fuel by creating air fuel mixture that can produce the desired results the producer want in his “hollywoodish” documentary, and in the process he insult the intelligence of the viewer, real life fuel tank is not like this.

It is very much the norm to conceder 1 part gasoline mixed (in a carburetor) with 14.7 part of air then subjected to compression (using piston) in hope to reach a critical mass where oxygen and fuel are well combined to produce a useful combustion in piston engine after ignition at sea level. This is just to give an idea of fuel/air ratio for something we know. For anybody who fly a Cessna (none fuel injected) he would be very much familiar with lean and rich fuel / air mixture, and when to lean out the mixture and when not. Basically it is adjusting the proper air/fuel ratio to optimize the combustion to produce useful power out of the engine when the altitude changes to accommodate the changing oxygen amount (actually oxygen density). Fuel tank doesn’t have pistons or atomization aid and it doesn’t change its volume.

Speaking of volume; so if we have 24 cubic meter of air at that altitude (thinner, low in oxygen content in comparison to sea level) and 3 cubic meter of JP-8 knowing that they are in layers with insignificant atomization, what would be the amount of energy that it can be produced to blow up the tank? Are fuel tank that frail?.

Fuel tank is very damp enclosure (water vapor mixed with fuel vapor) particularly in coastal area where the humidity is high. Aircrafts are known for having water collected in the tank due to the condensation of water vapor in the air that occupies the empty space in the tank. The accumulated water creates vapor (low pressure effect) making fire starting and propagation harder. In smaller aircraft, water level inspection in the fuel tank is part of the pre-flight procedure by actually taking sample.

In real life we are not anywhere near to have a significant fire in a fuel tank at that altitude neither the condition is conducive.

At this point, I will let you in a little secret:
B747 CWT vent is equipped with a float valve that blocks the vent in case of overfilling condition. Also, it will not allow fuel to come out when the aircraft is banking. The venting channels are interlinked with the other tanks (in the wing) and connected to a device called “surge box“at the wing tip and then to the atmosphere. This box regulates the pressure fluctuation and also keeps a little positive pressure inside the tank to reduce foaming. Further more, this will facilitate more fuel fume to escape to the wing tank and from there to the atmosphere during pressure changing, also allowing less air coming back to the center tank to equalize the pressure.

This design is approved by the FAA and Boeing engineers. As I said earlier about the inerting system, they didn’t see much of advantages for such a system, and the condition of the fuel tank designs are not notoriously life threatening knowing that jetliners are different breed of birds than military and aerobatics ones. There is so much DOT regulation on fuel and flammable vessels designs and safety that also didn’t change much the principle fuel tank design.

Reality dictate, hence the term “theory and practice”. You will be surprise of how many aircraft lost because of “fuel tank explosion” in mid air, search it, check out the FAA website (I don’t have the link right now) for the numbers. Safety shouldn’t be compromise for any reason and in my book any preventable loses of human life is not excusable.

The thing that troubled me the most is the elaborate effort using esoteric science to prove some thing scientifically not sound, tested over in real life for decades and proven it is no issue. At the end, people believe what they want.

[fueldrinker]

Is this just a Boeing problem or have other aircraft suffered?

:confused:

[IGh]

Fueldrinker asked about other tank deflagrations suffered by non-TBC airliners (above).

The AAR for TWA800 has an Appendix G that list some earlier cases, that cites Douglas cases (omitted many other examples).

The first modern investigation of an airliner ullage deflagration was in 1959, done by the Italian authority. That was Lockheed:


TWA 891 / 26Jun59, TWA Super Constellation L-1649-A N7313C flying near electrical storm. Broke-up in flight. Near Milan Italy, Vicinity of Olgiato Olona, Varese Province Italy....

... At disintegration altitude was between 11000' and 12000'; speed about 170 KIAS. Experiments concluded that critical variable existed for gasoline vapor ignition: tests in presence of non-static electrical discharge showed vapors ignite only if plane were CLIMBING. Uncertainty, vapor ignition tests only showed that "hazard cannot be excluded and vapors would actually ignite if the electrical discharge were non-static and sufficiently intense." Witnesses near site observed a lightning stroke, sound of explosion, then saw the fall of the plane's burning wreckage....

P.C. = from seven hypotheses , process of elimination discarded six; the remaining hypothesis deemed probable: Breakup due to explosion of fuel vapors in Fuel Tank #7, followed by excess pressure or further explosion in Tank #6; #7 Tank fuel vapors set-off by ignition of gasoline vapors from static electricity discharges (streamer corona) that developed at vent outlet.

Recommendation: More research and tests of fuel tank explosion, and instructions to pilots to avoid flight through such hazardous weather....

... Rpt of Board of Inquiry of Ministry of Defense, Republic of Italy, Rpt date Nov '60 (USA's CAA AAR File # 1-0045).]

= = = = / / / = = =

Here's another non-Boeing example:

British Eagle Int'l Airlines (BEIA) / 30Aug66 Britannia G-ARKA London, during pressure refueling at 0015 hrs an explosion occurred within starboard wing causing tank rupture and limited structural damage.

A/c had been on ground nine hours since flight, heavy rain at time of incident; crew onboard doing pre-flight checks. Few obvious ignition sources in region of tank, electrostatic discharge suspected within tank. First known incident of "ESD" in a civil a/c [numerous Canadian military a/c had suffered such tank explosions].

Conclusions from RAE Tech Rpt 67080, Apr'67, "Investigation into a Fuel Tank Explosion, Britannia G-ARKA" by M.E. Rogers & H.W.G. Wyeth reveal lack of evidence:

"... mist or foam generated by refuelling must have been ignited by an electrostatic discharge in the tank ullage. There is no positive evidence to support this choice of ignition source and, in fact, conditions seemed unsuitable for dangerous charge accumulation at the time of this incident. However all other ignition sources are discounted."

CRC Nov'75 "Aviation Fuel Safety" states this ullage as JetA vapors, low order tank explosion, moderate damage.

[The AAIB had several observers there at Calverton (wreckage collection at the old F-14 factory), Dave King managed to get co-workers to do a search, AAIB faxed that RAE rpt within a few hours. AAIB guys told us they were surprised that AAIB had passed that case to the RAE for investigation.]

[clearedtocross]

Bristol Britannia did run on jet fuel (Proteus turboprops), but the Super Constellations ran and still run on AVGAS (gasoline).

[skiingman]

This is old, but I'm a pedant:

Secondly, car fuel pumps are usually not submerged in the tank, but somewhere down the line, which their electrical parts away from the fuel line.

This has been largely false for twenty five years or so. Even early EFI cars with downstream pumps usually had an in tank pump as well. Most modern fuel injected gasoline cars have a sole pump in the tank, submerged in fuel when full. Direct injection systems go back to the old days of engine driven pumps, but still have in tank pumps AFAIK.

Also, you speak of venting. In the context of gasoline automobiles, evaporative emissions are controlled by simple and robust systems. The moisture and fuel contamination problems that kill people in aircraft are extremely uncommon in modern automobiles. I have a vehicle I drive twice a month or so that runs on the same tank of fuel for months with zero issue. (It also does other things that appear to be magic compared to most light aircraft, such as always starting on the first try, never fouling plugs, consuming practically no oil at 15 years old, etc.)

Jet-A, of course, works much differently. I would be very interested in learning how much HC leaves a large airliner in typical use. I would assume the evaporative part is minuscule compared to the poorly combusted part, but I'm curious nonetheless. I expect refueling is the biggest offender.

[35hPA28]

On a side note, DC documentaries can be quite pasteurized. I recall watching one ( Mayday/Crash Scene Investigation) about AA965 and no mention at all was made about any discussion between pilots and cabin crew union/ERC representative on board regarding delays at Miami and possible too long on-the-clock time leading to the need for the crew to take an extra day´s rest before the return flight, as per regulations. IIRC, that was pointed as a contributing factor to the accident.
Added to clarify: ...pointed as a contributing factor by investigators.