The same way they did after the unexplained battery overheats :eek:

(did I say that)

Aviation week article
 

has a few great articles on this issue

1) fire did NOT burn thru airframe- but claims aluminum section would have been weakened more and possibly failed
2) Boeing is planning on fixing - several possiblities in work patch to ferry, replace aft section, etc
Issue will be out monday- but those who have subscription can access via zinio

partial quote via ocr
....Insiders also quietly note that the
composite structure heldup well to the
fire. Compared to conventional aircraftthickness
aluminum, for which FAA
tests have shown burn-through timesof
30-60 sec. in intense fires, Boeing flame
tests exhibited longer burn-through
times for sections representative of
the 787's composite laminate skin. The
aircraft maker also points out that although
the fire was severe enough to
visibly char the exterior of the skin, the
fire did not penetrate the surface."

"This is the largest incident that I
have seen as far as damage from heat
and fire," says Paul Jonas, director of
environmental test labs and special programs
at the National Institute for Aviation
Research at Wichita State University,
"This is a significant event. It does
look like a lot of heating." He estimates
that fire temperatures may have been in
the 1,000-1,200F range to cause the type
of paint damage seen in photographs of
the scene. "Composites are pretty much
self-extinguishing. If you put flame on
and take it off, it doesn't propagate."

I will not copy more

Interesting that halon was used (bcf) in this incident as reported in a previous post, now the 1st ba team initially entering the a/c would've had either a high pressure hosereel or a 45mm line of hose for their own protection and to extinguish the fire.

The fact that ba team(s) were used, that all takes time to implement the correct ba procedures, who made the call for bcf, the time taken for it to be deployed, looking at the pictures posted it was a good job done by heathrow airport fire service.

What hasn't been said is how long it took to extinguish the fire, maybe the fire integrity is better than thought.

amicus
 

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? :confused:

Reuters:

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.

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. ;)

- 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'?

I would have thought "a hole".

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.

OK - Now that SRMman has sorted that for us, are we looking at a 'hole' or sooting/discolouration?

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

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.

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.

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?

From the New York Times
http://www.nytimes.com/2013/07/20/bu...-wire.html?hpw

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.

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...

If there are no "holes", what did ATC spot that made them think "fire"?

joyride
 

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.

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.