TWA 800 - Changed the World?

[twistedenginestarter]

There was an interesting programme on C4 last night showing the incredible investigation into TWA 800. Unfortunately they implied the results had changed aviation.

Tell me I'm wrong but absolutely nothing has changed has it? There are still 747s with the same fuel tank and wiring risks, all over the world as we speak.

Incidentally they seemed to be saying it was a high voltage getting into a low voltage sensor line but that the spark was caused by residues that form over long periods when connections are immersed in fuel - so Kapton is not to blame?

[Jackonicko]

I just hope that the "It was a bomb/it was a missile" conspiracy theorists watched what was a succinct and compelling explanation of what happened and why, and which even put faces and names to those responsible for the NTSB's conclusions - ordinary dedicated scientists whose very existence makes the idea of some shadowy plot seem even more far-fetched.

What a great series Going Critical has been - entertaining and informative - superb journalism. Hats off to those responsible!

[John Farley]

twistedenginestarter

I seem to remember reading that quite a lot of changes were made to reduce the risk of a similar chain of events. Things like wiring inspections, minimum amount of fuel to be carried in the tank when driving the air con hard on the ground and so on.

Perhaps a 747 mate can enlighten us.

Well said Jacko BTW

[Dagger Dirk]

Read the quoted story below and you might begin to appreciate that they have known all along what caused TWA800 to explode. When you have read all that was known (below) and then (right-click "save as..") downloaded and viewed the colour photos from the parent pdf (acrobat) file at this link (http://www.iasa-intl.com/PDF/FUELTANKTERMINALSTRIP.pdf), you will appreciate that:

a. silver-soldered terminal connections interact with the sulfur in JetA fuel to form conductive silver-sulfide deposits. The accumulation of these electrically conductive deposits on fuel tank FQIS terminal blocks means that there is a breakdown in that terminal block's insulation and as little as a 9 volt transistor radio battery can cause an arc across that FQIS terminal block. So we might conclude that not a lot of misdirected electricity was required to ignite that centre wing tank of TWA800 (or the 737's in Manila and Bangkok). The aging wire and a minor amount of induced current was all that was required to arc across the FQIS terminal block.

b. Smiths Industries and many other responsible manufacturers of intank electrics have been very quietly changing over to nickel-plated terminations on wiring, hoping that this nasty problem will just "go away".

c. The FAA has decided that a quiet program with the cooperation of the relevant sections of industry is in everybody's best interests. It would, after all, be a huge program to swap out all immersed silver-soldered wiring in fuel-tanks, wouldn't it?
Boeing Analytical Engineenng Report 2-5323-WP-91-97, dated March 10, 1991. that described Boeing's examination of sulfide deposit, on a harness from a fuel quantity indicator from the right wing tank of a 757, The fuel quantity indicator had a documented history of iregularities after only 750 hours in service. The report noted "it is readily observed that the contaminant has migrated up into the conductor even after only 750 hours in service".

Boeing Laboratory Report 9-5576-P+CA-025P, dated March 30, 1993, that described sulfide deposits on electrical hardware from the fuel tanks of 737, 747, and DC-10 airplanes.
Boeing Laboratory Report 95576-P+CA-025P1, dated April 29, 1993, that also described sulfide deposits on electrical hardware from the fuel tanks of 737, 747 and DC-1O airplanes and included two additional reports obtained through a literature search): Silver Corrosion by aviation Turbine Fuel , dated September 1970. written at the Journal of the Institute of Petroleum; and Copper and Silver Corrosion by Aviation Turbine Fuels, dated April 22, 1973 written at the Indian Instituteof Petroleum.
Boeing Analytical Engineering Report 9-5576-WP-97-272, dated August 5th 1997, that described electrical tests of FQIS parts containing sulfide deposits.

During FAA-sponsored tests conducted in response to Safety Recommendation A-98-37 (issued as a result of this accident) researchers at the University of Arizona also used the method developed by UDRI to create silver-sulfide deposits in a laboratory. During subsequent tests, these deposits served as an ignition mechanism for Jet A fuel vapor. The results of these tests were discussed at a November 9, 1999 meeting involving FAA, Safety Board. and industry personnel. According to University of Arizona personnel, the formation of sulfur-containing conductive deposits from Jet A fuel on silver wire occurred with both a.c. and d.c. current Additional tests in this area are ongoing".

In response to AFRL's findings from the 1990 vapor ignition incident. BFGoodrich eliminated the use of silver-plated components in the FQIS and began using nickel-plated wire, gold-plated ring connectors, and sealant Those improved components have been used in military airplanes since about 1993. According to BFGoodrich, since that time there has been a large reduction in the FQIS anomalies that had associated with silver sulfate deposits (such as FQIS innacuracies. Although a Boeing 1991 engineering report indicated that silver should never contact sulfur-containing liquids because of the susceptibility to sulfidation, and Boeing uses nickel-plated (instead of silver-plated) wiring in its newly manufactured 777 and 737-NG airplanes, Boeing indicated in a December 7, 1999, letter to the Safety Board that it does not recommend replacing silver-plated FQIS components in existing airplanes.

[Mycroft]

TES
re - Kapton wiring not the problem..
the problem with kapton insulation is that it has a tendency to crack. The ignition source for TWA is believed to be high voltage from the generator cables crossing through faulty insulation to the low voltage fuel monitoring circuits. Thus faulty (kapton) insulation was an important factor (no spark- no bang)

[Jackonicko]

But if you look back at threads on R&N, there were dozens of conspiracy theorists convinced that it was a missile/bomb/little green men. Don't they read tech log?

[Blacksheep]

Most of the tank harnesses in B747 Classics were crimped connections rather than the current soldered connections. (Of course TWA 800 may have had upgraded wiring installed as a modification) The possibility of arc-over isn't a function of voltage it also depends upon energy. The power applied to the tank units from the FQIS is much too low to supply a spark - the measurement principle is based on capacitance and doesn't require even as much energy as the battery in your watch let alone the 9 volt battery that someone mentioned. If the tank wiring was the source of ignition it would need to have come from an external short circuit. That in turn would have caused FQIS indication problems. Short circuits in wiring usually develop over a period of time and cause intermittent defects for weeks preceding a hard fault. There is nothing in the maintenance history of TWA 800 to suggest such a sequence. Admittedly it's not impossible, merely unlikely. There are plenty of other possible sources of ignition and most of them have now been addressed by a number of ADs and design reviews/changes. We all hope that the potential for a repeat of such a catastrophe has been eliminated, but caution is needed. We still do not know, and never will know, the precise cause of the fuel tank explosion that resulted in the loss of TWA 800.

So carry on surmising and supposing and ooh-ing and ah-ing about the various pet theories, without getting dirty hands or stinking of jet fuel crawling through the confined space of an airliner fuel tank. Searching for corrosion, chafing, lose bits and cracks. Whether you see them or not you're all still relying on the vigilance of the maintenance engineering staff; a much maligned, despised and underpaid group, most of whom nevertheless continue to perform quiet miracles in the background. TWA 800 was lost. I prefer to think of all the piles of quietly rotting aluminium and chafing insulation that, thanks to the efforts of vigilant inspectors, continue to fly safely on their way.

**********************************
Through difficulties to the cinema

[richmond45]

Wing Box was intact so how did the fuel tank explode? You guys gotta be kidding. Not even the Chief FBI Investigator believes that the center tank exploded. 747's fly with the Center Tank empty all the time. Hint Clinton Administration - pre election - just another coverup of the many that occured.

[Epsom Hold 2]

I don't think it changed the world, a very old plane had an electrical fault. A very sad event to be sure but not an unprecedented one.

Cover-up my arse. It's hard enough to keep a secret between two people, let alone hundreds. THAT SAID, has anyone seen that photo of a couple arm in arm on the deck of an outdoor restaurant on Long Island that night (the photo even has one of those nasty-looking digital camera date stamps on it)? Clearly (albeit in the far distance) in the sky: a missile. Don't know what to make of that at all.

[HotDog]

richmond45, I don't know where you get your info from but I can tell you a fact of my operation of 10,800 hours on the Classic 747. 80% of our long haul ops required varying amounts of fuel in the centre tank up to it's full capacity of 12,890 US gallons.

[John Farley]

Epsom Hold 2

Re the pic you mention, my wife adds and subtracts things to/from her pictures according to her mood or who is doing what to whom. As yet she has no reason to be interested in SAM’s.

[richmond45]

Hot Dog - 747 -100 and -200 Center fuel Empty on US to Europe Flights 90% of the time. My year of experience with Euro - Charters - almost never.

[GlueBall]

Mycroft says: "No Spark, No Bang."

Ever heard of spontaneous ignition? Heat and compression; you know, as in a diesel engine,...which has no spark plugs.

Fact is, contained fuel vapors can ignite under intense heat and pressure. Likewise, a partially clogged vent during climb could contribute to overpressure.
:eek:

[blended winglet]

all very scary indeed, I think I'll go back to gliders !!!
:eek:

[TowerDog]

Uh slow down GlueBall:

Diesel fuel ignites due to heat and pressure from a 20-1 compression ratio.
You are indeed rigth that jet fuel could ignite under the same conditions: Inside a diesel engine that is.

Even if your jet had clogged vents and ram-air built up pressure inside the fuel tanks,
(Or pressure build-up from clogged vent and return fuel being pumped into tank)
uh, the wing would most likely rupture long before there was enough pressure to cause ignition from compression.

I would guess the fuel tanks could only take a couple of PSI before failure, the burn chamber in a diesel probably has several hundred PSI. (Or thousands or millions: Where is the engineers when ya need 'em??)

As far as what happened to TWA 800, the more I learn about that accident, the less sure I become: Fuel tank problem, missile, or some other factor. (Fuselage fatigue, wing spar snapped, engine explosion, bomb, whatever)