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Ethiopean 787 fire at Heathrow

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Ethiopean 787 fire at Heathrow

Old 20th Jul 2013, 02:49
  #561 (permalink)  
 
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amicus

Speed of sound,
Codswallop, total and utter codswallop.
So given the fact that none of these ELTs have been known to have started a fire onboard before, you don't think it is worth examining other ELTs which have undergone similar environmental changes to the 'incident unit', ie sat installed but unused for over three months?

Reuters:
The Ethiopian Airlines plane sat outside in the hot African sun for months, raising questions about whether that could have affected the battery in the locator beacon, said the source.

Last edited by Speed of Sound; 20th Jul 2013 at 09:24. Reason: Edited to add quote from Reuters
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Old 20th Jul 2013, 06:06
  #562 (permalink)  
 
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Island Airphoto,
Not all ELT have Lithium chemistry batteries, or even NiCad.
However, see my last post about my personal experience with both Li and NiCad consumer batteries having a thermal runaway and burning, the Li was an AA size, the NiCad was a 9V battery.
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Old 20th Jul 2013, 06:39
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Fire investigation is a specialty field of its own. Based on what little I know about it from a colleague who's father was a noted specialist in the field, it can be a painstakingly long process to pinpoint the cause of some fires. While TV and movie investigators always seem to be able to reach their "Eureka!" moment in an hour or so, that is not always the case in the real world.
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Old 20th Jul 2013, 07:32
  #564 (permalink)  
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Originally Posted by DWS from Av Week
fire did NOT burn thru airframe
- yet the picture at post 54 looks to me like skin penetration other than fire-axe chopping? What exactly is the definition of 'burn thru'?
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Old 20th Jul 2013, 07:48
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I would have thought "a hole".
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Old 20th Jul 2013, 07:54
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It certainly does look like the skin has burnt through to reveal internal structural members, but perhaps it is just charring and the thicker structural members have shielded adjacent skin enough to prevent charring, as if they have left shadows of themselves.
Still, I think it was Amicus who posted the info that at just 300 degrees the composite looses half its strength, and this fire sounds like it was a lot hotter than that, so my guess is that any repair will have to cover a much larger area than just the charred area.
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Old 20th Jul 2013, 08:03
  #567 (permalink)  
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OK - Now that SRMman has sorted that for us, are we looking at a 'hole' or sooting/discolouration?
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Old 20th Jul 2013, 09:12
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Reuters: "Condensation, humidity and installation - that's the focal point of the investigation," the source said."

Exclusive: Probe of Boeing's 787 focuses on condensation, emergency beacon | Reuters
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Old 20th Jul 2013, 09:44
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BOAC,
Just looking back at the AAIB Report, they say: " ...examinations of damaged areas revealed that the greatest heat damage and highest temperatures were centred on the rear fuselage close to the crown ... and corresponds to the most damaged external areas, with blackening and peeling paint and damage to the composite structure."

Ref the last part (my italics) I would say that there is no 'hole' as such; I imagine that the Report would have used expressions like 'damage including penetration' had this been the case.
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Old 20th Jul 2013, 10:00
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That report is interesting, it sounds like they are investigating condensation, humidity, corrosion (oxidation), thin insulation and isolation. I wonder if these possible contributory factors could also have contributed to other known electrical and battery problems. It would not surprise me if 787s have to undergo wiring and air conditioning modifications. This would reduce some of their economic advantages, but perhaps be what is needed to improve it.
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Old 20th Jul 2013, 10:11
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Remember the bulk of the wiring is standard copper, I believe the use of aluminum was mostly restricted to the very heavy gauge (aka gage) power stuff. The term 'isolation' caught my eye - I wonder if they mean thermal or electrical?
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Old 20th Jul 2013, 10:16
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From the New York Times
The 787ís cabin maintains a higher humidity level than other jets to increase passenger comfort. One theory is that the humidity could have created condensation that caused a short circuit in the battery or its wiring.

Another concern is that the composite skin absorbs more heat from the sun than the aluminum on other planes. That has prompted questions about whether the battery in the transmitter could have been degraded by excessive heat from the skin.
http://www.nytimes.com/2013/07/20/bu...-wire.html?hpw
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Old 20th Jul 2013, 11:10
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A couple of thought: Thousands of similar ELTs are used every day without incident, but that doesn't rule out the possibility that this one made it off the assembly line with a defective battery or diode.

Many high-strength aluminum alloys -- for example 7075 -- are artificially aged at around 300 degrees Fahrenheit. Heating them to or above this temperature will start to affect their mechanical properties, possibly quite significantly. There are stories floating around about aluminum scuba tanks that exploded because heat lamps were used to cure a new coat of paint.

I don't know whether aluminum or composite would resist fire damage better, but it's not as simple as looking at the melting point of aluminum.
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Old 20th Jul 2013, 11:27
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I don't know whether aluminum or composite would resist fire damage better, but it's not as simple as looking at the melting point of aluminum
As you say, not a simple answer.

One area AL may have proved better here is it is a far better heat conductor. So if / while there was a relatively "small fire", the AL skin will conduct away the heat and keep the skin temperature lower.

IIRC the Boeing Tests seen elsewhere were not looking at this aspect, but a blowtorch concentrated on a small skin section. I wonder if that was as realistic as some of the "battery tests" they did?

amicus' thoughts / papers as ever discuss at length...
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Old 20th Jul 2013, 11:42
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Ref the last part (my italics) I would say that there is no 'hole' as such; I imagine that the Report would have used expressions like 'damage including penetration' had this been the case.
If there are no "holes", what did ATC spot that made them think "fire"?
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Old 20th Jul 2013, 11:58
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joyride

I wonder if these possible contributory factors could also have contributed to other known electrical and battery problems.
Condensate was said to be often found in the original battery boxes of 787 Li-Ion Mark I.

This may be one of the reasons that a hermetically sealed blue box was designed for the 'fix'. To keep combustion gases in and to keep water vapour out.
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Old 20th Jul 2013, 14:06
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Interesting.

My understanding is that Teflon, unlike some plastics (eg Nylon and Delrin) does NOT absorb any water. However, we have heard that the 787 has a very thin layer of Teflon to save weight, so I wonder if there is a possibility of flaws in this coating or wear/abrasion damage.

Powder Coated steel can rust anywhere the steel is exposed by flaws or chips in the powder coat, or if the steel is not thoroughly de-rusted before coating. The rust spreads along beneath the powder coat until it starts flaking off, to a faster and greater extent than painted or stove enameled steel.

I am wondering whether aluminium wiring, exposed anywhere to a hot and humid environment, could behave in a similar way to powder coated steel, and oxidise faster than usual and cause increasing damage to the thin Teflon coating.
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Old 20th Jul 2013, 14:10
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This may be one of the reasons that a hermetically sealed blue box was designed for the 'fix'. To keep combustion gases in and to keep water vapour out.
More than that.... Their "solution" of putting a battery in a box, which looked like avoiding a problem they didn't understand.... included "drain holes" for the battery....

http://assets.sbnation.com/assets/23...on-English.pdf

Maybe Boeing had worked out what the real problem was and that's why they were so confident that it wouldn't happen again.

Perhaps they could buy some more boxes to put electrical stuff in.
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Old 20th Jul 2013, 14:28
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Doesn't matter anyway....just remove the ELT

Safety Breaking News: Japan to Let Carriers Remove 787 Emergency Beacons | Watch the video - Yahoo! Screen
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Old 20th Jul 2013, 15:30
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If there are no "holes", what did ATC spot that made them think "fire"?
Smoke;

Tmperatues sufficient to darken the outside as seen in the photos would also release smoke from the outside surface as it was toasted.
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