FAA Fix For Fuel Tank Explosions
Repositioning Boeing center tank fuel pumps into an adjacent main tank would preclude the greatest volatility of center tank explosions.
What do the fuel pumps have to do with volatility.?
Anybody willing to translate this into engineering terms.
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Yes, lomapaseo: No need to get into engineering minutea about "spontaneous combustion." It is self evident, for example, that if one puts a piece of paper on something that gets very hot (but doesn't glow or burn), like maybe on a hot brake...and you'll see that the paper will burn without a flame or spark. Another example would be like a diesel engine ...which has compression and combustion without the benefit of ignition (spark plugs)...you know a little about pressure and heat, don't you?
If you read a little about the Thai Airways B734 center tank explosion you'll learn that the center tank pump was running dry, for whatever reason, whether it was a faulty thermal cut-off switch, or whether it was a faulty flow control switch...the end result was that the pump got so hot and either caused a spontaneous fuel-air-vapor combustion, or caused insulation on electrical connectors or wiring to become frayed from excessive heat which may have generated a spark...
The facts are that Boeing has a history of center fuel tank explosions...and Douglas doesn't. Thirty five year old DC8s today are still plowing the skies ...with 35-year-old fuel tank wires and no fuel tank explosions. Additionally, Douglas uses "feed box" design which keep main tank pumps, positioned inside the feed boxes, always fully submerged and primed.
Positioning center fuel tank pumps inside adjacent main tanks is a variation of fail safe fuel system design philosophy.
If you read a little about the Thai Airways B734 center tank explosion you'll learn that the center tank pump was running dry, for whatever reason, whether it was a faulty thermal cut-off switch, or whether it was a faulty flow control switch...the end result was that the pump got so hot and either caused a spontaneous fuel-air-vapor combustion, or caused insulation on electrical connectors or wiring to become frayed from excessive heat which may have generated a spark...
The facts are that Boeing has a history of center fuel tank explosions...and Douglas doesn't. Thirty five year old DC8s today are still plowing the skies ...with 35-year-old fuel tank wires and no fuel tank explosions. Additionally, Douglas uses "feed box" design which keep main tank pumps, positioned inside the feed boxes, always fully submerged and primed.
Positioning center fuel tank pumps inside adjacent main tanks is a variation of fail safe fuel system design philosophy.
Last edited by GlueBall; 23rd Feb 2005 at 13:03.
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GlueBall,
Partially agreed; dry running of pumps is not a clever idea.
But: You can also prevent dry running of pumps when they are located inside a transfer/reserve tank. Routing of the attached plumbing is the trick.
Furthermore, you can build pumps and the pump canisters explosion proof. Today´s pumps can run dry extensively, and you can even throw tons of debris into them - you won´t see an ignition source. Yet, if there would be one, flame traps would prevent propagation.
Finally, thermal fuses are installed to prevent overheating of the pump.
I probably forgot some devices; nevertheless: Future fuel systems should be pretty safe!
Cheers,
J.V.
Partially agreed; dry running of pumps is not a clever idea.
But: You can also prevent dry running of pumps when they are located inside a transfer/reserve tank. Routing of the attached plumbing is the trick.
Furthermore, you can build pumps and the pump canisters explosion proof. Today´s pumps can run dry extensively, and you can even throw tons of debris into them - you won´t see an ignition source. Yet, if there would be one, flame traps would prevent propagation.
Finally, thermal fuses are installed to prevent overheating of the pump.
I probably forgot some devices; nevertheless: Future fuel systems should be pretty safe!
Cheers,
J.V.
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The FAA has recently concluded flight tests on both an A320 and a NASA 747, of a simplified OBIGGS system for fuel tank inerting. The following FAA .pdf reports discuss the OBIGGS system design used on each aircraft, flight test parameters, and test results. They are interesting reading for anyone interested in the current state-of-the-art in on-board nitrogen gas generation fuel tank inerting systems.
Airbus A320 flight test results - June 2004 - 1.25MB
NASA 747-100 flight test results - December 2004 - 8.8MB
Airbus A320 flight test results - June 2004 - 1.25MB
NASA 747-100 flight test results - December 2004 - 8.8MB
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Flight Safety,
Yep, and they have just issued Special Conditions for a 747 Flammability Reduction System:
http://www.airweb.faa.gov/Regulatory...C?OpenDocument
Thanks for the links!
Cheers,
J.V.
Yep, and they have just issued Special Conditions for a 747 Flammability Reduction System:
http://www.airweb.faa.gov/Regulatory...C?OpenDocument
Thanks for the links!
Cheers,
J.V.
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I read somewhere that the simplified OBIGGS used for the 747 test weighed in at about 100 pounds, and would be lighter for smaller aircraft. That's not bad.
The only real issue I see from the flight tests, is a noted degradation in the performance of the ASMs (Air Separation Modules - contained the hollow fiber membranes) that accumulates with usage time. The cause is not know yet, and could effect the long term performance of these systems. It is known that hydrocarbons and HFMs don't react well together, and particulate matter tends to clog the HFM, so maybe these are the causes.
The only real issue I see from the flight tests, is a noted degradation in the performance of the ASMs (Air Separation Modules - contained the hollow fiber membranes) that accumulates with usage time. The cause is not know yet, and could effect the long term performance of these systems. It is known that hydrocarbons and HFMs don't react well together, and particulate matter tends to clog the HFM, so maybe these are the causes.
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The only conspiracy theory worth commenting on concerns Ustica (Moderators: can't you find a separate home for TWA800 conspiracy theorists?). The Itavia DC-9 was, as near as could be scientifically determined, broke up in flight after a bomb blew up in the toilet. That was the near-certain conclusion (near only because he is an appropriately conservative investigator) of Frank Taylor, recently retired head of Cranfield Aviation Safety Institute in a highly detailed report several years ago commissioned by the Italian investigating magistrates and published in a past issue of the journal of the International Society of Air Safety Investigators.
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inerting cost
Earlier posts mention estimated compliance costs for the new system.
Methinks the astute beancounter will be looking for savings, not costs. For example, there should be a measurable savings in hull and liability insurance cost, once the inerting system is mature enough to save an airplane every few years.
It's usually too easy to point to costs, without considering the flipside.
Methinks the astute beancounter will be looking for savings, not costs. For example, there should be a measurable savings in hull and liability insurance cost, once the inerting system is mature enough to save an airplane every few years.
It's usually too easy to point to costs, without considering the flipside.
Earlier posts mention estimated compliance costs for the new system.
Methinks the astute beancounter will be looking for savings, not costs. For example, there should be a measurable savings in hull and liability insurance cost, once the inerting system is mature enough to save an airplane every few years.
It's usually too easy to point to costs, without considering the flipside.
Methinks the astute beancounter will be looking for savings, not costs. For example, there should be a measurable savings in hull and liability insurance cost, once the inerting system is mature enough to save an airplane every few years.
It's usually too easy to point to costs, without considering the flipside.
After that you may argue about the saving of one B747 in some many years (is it 1 out of 20 yrs? and maybe argue for 10% of this as kickback insuree credit spread out over all operators of the type.
extremely insignificant compared to the costs of the retrofit.
