Belgique
12th Feb 2003, 13:12
1. As a result of the TWA800 findings the FAA brought out SFAR88 which required all manufacturers and operators to compulsorily rat around, find and take steps to positively eliminate all sources of ignition in fuel-tanks.
2. As a result of that (mainly electrical) witch-hunt it was found that:
a. There were far too many sources of ignition in and around fuel-tanks for there to be any real hope of eliminating them with any confidence.
b. During the installation of the (mandated) Smith's modified FQIS on the classic 747's it was found that the TSU's (transient suppression units) were being affected by some unknown mechanism within the tanks - and as a result the fuel quantity indicators were erratic and unreliable at best. It was found that the problem was a silver sulfide build-up on the terminal blocks. This came naturally from an unholy marriage of the sulfur naturally occurring in the fuel and the silver used in silver solder (used in most connectors/lugs etc). This deposit across the terminal blocks (and elsewhere) was so conductive that a 9V transistor battery across the terminals could easily produce a spark.
3. Obviously the FAA wasn't about to mandate the replacement of all silver-soldered electrical components with nickel-plated ones (nor advertise that that was a problem) so they suddenly had a change of mind about the other solution to tank explosions - inerting. Suddenly last summer they announced that there had been a breakthrough in inerting technology and that it was, after all, to become an AMOC (alternate Means of Compliance). But once you read into the fine print, they hadn't actually decided upon a definite technology and inerting was perhaps a too strong term. The OBIGGS inerting would mostly eliminate oxygen molecules most of the time (but certainly not all of the time). Airbus wrote back and claimed that it would be providing "two levels of safety" if manufacturers (or operators) could decide on either
a. explosion-proofing their a/c electrically or
b. explosion-proofing their a/c atmospherically BUT
c. Not unnecessarily (or mandatorily) doing both
4. Various academics have criticized the inerting solution as being incomplete (and very expensive) and just as many have said that they would have no confidence in the electrically inerting methodology. Some have said that implementation of both would accord a higher level of safety - but the FAA isn't considering that as a solution (i.e. one is an AMOC for the other).
5. It seems to me that we may be overlooking alternative or complementary solutions here.
a. It has been pointed out (on the overheating fuel-pumps thread) that there are other measures that can reasonably be taken in new aircraft (positioning CWT pumps in much cooler/unheated wing-tanks). And there is a very lightweight mesh (Explosafe -search on Google) that has a fine track record and only reduces tank volumes (but not luggable fuel weight) by about 2%. http://www.iasa-intl.com/imagery/gash/cat1315.jpg
b. But I seem to recall also that back when I started in jet aviation that the kero we burnt then was a much higher flash-point than that in use today. Surely the answer should be not to have to carry an OBIGGS system around or have expensive GSE as just another obstacle on the ramp (and another reason for late departures) - by simply raising the flashpoint on the fuel. It might cost one or two BTU's/lb fuel carried - then again it may not.
Does anybody have an idea?
2. As a result of that (mainly electrical) witch-hunt it was found that:
a. There were far too many sources of ignition in and around fuel-tanks for there to be any real hope of eliminating them with any confidence.
b. During the installation of the (mandated) Smith's modified FQIS on the classic 747's it was found that the TSU's (transient suppression units) were being affected by some unknown mechanism within the tanks - and as a result the fuel quantity indicators were erratic and unreliable at best. It was found that the problem was a silver sulfide build-up on the terminal blocks. This came naturally from an unholy marriage of the sulfur naturally occurring in the fuel and the silver used in silver solder (used in most connectors/lugs etc). This deposit across the terminal blocks (and elsewhere) was so conductive that a 9V transistor battery across the terminals could easily produce a spark.
3. Obviously the FAA wasn't about to mandate the replacement of all silver-soldered electrical components with nickel-plated ones (nor advertise that that was a problem) so they suddenly had a change of mind about the other solution to tank explosions - inerting. Suddenly last summer they announced that there had been a breakthrough in inerting technology and that it was, after all, to become an AMOC (alternate Means of Compliance). But once you read into the fine print, they hadn't actually decided upon a definite technology and inerting was perhaps a too strong term. The OBIGGS inerting would mostly eliminate oxygen molecules most of the time (but certainly not all of the time). Airbus wrote back and claimed that it would be providing "two levels of safety" if manufacturers (or operators) could decide on either
a. explosion-proofing their a/c electrically or
b. explosion-proofing their a/c atmospherically BUT
c. Not unnecessarily (or mandatorily) doing both
4. Various academics have criticized the inerting solution as being incomplete (and very expensive) and just as many have said that they would have no confidence in the electrically inerting methodology. Some have said that implementation of both would accord a higher level of safety - but the FAA isn't considering that as a solution (i.e. one is an AMOC for the other).
5. It seems to me that we may be overlooking alternative or complementary solutions here.
a. It has been pointed out (on the overheating fuel-pumps thread) that there are other measures that can reasonably be taken in new aircraft (positioning CWT pumps in much cooler/unheated wing-tanks). And there is a very lightweight mesh (Explosafe -search on Google) that has a fine track record and only reduces tank volumes (but not luggable fuel weight) by about 2%. http://www.iasa-intl.com/imagery/gash/cat1315.jpg
b. But I seem to recall also that back when I started in jet aviation that the kero we burnt then was a much higher flash-point than that in use today. Surely the answer should be not to have to carry an OBIGGS system around or have expensive GSE as just another obstacle on the ramp (and another reason for late departures) - by simply raising the flashpoint on the fuel. It might cost one or two BTU's/lb fuel carried - then again it may not.
Does anybody have an idea?