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.

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.

Doesn't matter anyway....just remove the ELT

Safety Breaking News: Japan to Let Carriers Remove 787 Emergency Beacons | Watch the video - Yahoo! Screen

Smoke;

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

ELT's are supposed to be watertight, and the Honeywell unit looks to be built like a tank (with I price tag to match I would guess :} )

There are Lithium powered 406's in the tails of King Airs all over the world, sitting on the ramp from Phoenix, to Miami. I doubt the cabin of a 787 is a worse environment.

I don't know quite what to think anymore.... :(

Or:If L2 was left open (hot day)? maybe the smoke was coming from there..?

Boeing 787 probe looks at condensation, wiring
 

Reuters reports:

So the FAA have chosen to ignore another safety recommendation. Marvellous.

Wet Were fires
 

back when the Lpckheed Jetstar came out, they had some peculiar fires involving the wiring. The installers were saving time in routing wires through clamps by using a bent set of needle nosed pliers to pull wites though. The teeth damaged the insulation leaving small pinholes.
Iworked at Lockheed New York and we viewed some films the investigators took through microscopes. of similiarly damage wires. The wires were charged to 28V DC and high humidity introduced. Under the microsope you could see, obviously in time lapse photography, a slow growth of copper crystall form between the cinductor, through the damage and work its way to the airframe which was at ground potential. The small current leak, using the moisture as a conductor was forming a thin film heater which in time grew to the point where it caused a fire. Lockheed New York rewired a number of Jetstars including some Air Force VIP aircraft.
The talk here of condensation and humidity coupled with a constant electrcal potential from a battery makes me wonder if the same mechansm might be at play in the 787.

Views of section 47/48 that give an idea of insulation fitment:

http://i337.photobucket.com/albums/n...psf43245fa.jpg


http://i337.photobucket.com/albums/n...ps4718781a.jpg

Interesting that Machaca's Reuter link was at 10.16 pm, the one in post 592 was at 6.37 pm and made no mention of pinched wires, clearly additional info led to the edited version. It is all starting to make sense.

On wires and pinoles and damage
 

Interesting- not too long ago there was an article ( in a boeing publication as I recall ) about some major cost savings being implemented on the 737 program re wiring. Thge story went like this . At various suppliers tom prewired body and cockpit assemblies, the wire bundles were temporarily held together by plastic zip ties- ties by the hundreds as it turns out. So as they go to final assembly and routing, the ties had to be cut/removed and in some areas replaced after re routing. In the process, wires were sometimes nicked by the snippers used- and thus repairs/rewiring was a small but continuing issue. Someone suggested cost savings- it took about 2 years to implement- to use some form of removeable tape for the wirebundles instead of zip ties. Virtually eliminating the cuts and damage, etc and saving a lot of time.

Wonder if the 787 implemented the same method. ?? IMHO - I doubt it. It takes a long time to coordinate with ALL the suppliers, provide the tape, etc

I'll try to find the article and post it here later


Boeing’s Renton plant bustling despite job cuts elsewhere | Business & Technology | The Seattle Times


... The rate increases are achieved not only through reconfiguring the assembly lines but also through changes, suggested by employees, that can be small but have a dramatic impact.

On a tour of the assembly lines, Nishma Shrestha, lead engineer on 737 wire-installation design, said Boeing cut 15 hours of labor out of final assembly for each 737 with one change: having suppliers bundle wiring together with tape instead of plastic zip ties.

The plastic ties had required assembly mechanics to laboriously snip off the little nubs on more than 5,400 ties around the many wire bundles that go into each plane. The task was time-consuming and frequently led to mishaps with cut wires.

This apparently simple change, prompted by a study in 2010, required complex coordination and was finally implemented on all 737s in January....

Could well be! If your box is not hermetically sealed (and most of the 'internal' electronics boxes are not) then it is required to provide drain holes to prevent condensate entrapment. This means all electronics, wiring and connectors within the box are expected to cope with a humid environment - all pcbs conformally coated and so on.

Every piece of equipment is tested for function under high humidity as part of qualification testing.

If the ELT is intended to be sealed - which it would be the case for equipment with an immersion spec - then it will not be expecting to be damp inside and I guess may not work too well if it is! The post above mentioned a 'wire entrapment' I suppose if Dr Murphy's law is working, that could have been the sole cause, wire trapped preventing case closing and sealing correctly plus insulation damage.....just a thought

Would be good for Boeing to become transparent about this whole issue....

Can't speak for the whole thing, but the bit I worked on (very early line numbers) the trailing leads for my system were coiled and taped up with the connectors nicely done up in a protective plastic bag.

I'm sure they will be, once all the facts are in. I'm not sure if you mean about testing, but humidity tests for electrical equipment are standard across the industry - either to DO160 or the manufacturer's in-house standards.

If any wires were to become pinched, and if these wires only had a very thin layer of Teflon insulation, rather than much tougher PVC based coverings....

I have tried to troll trough all the info but cant see to find if there is any info as to why it set on fire yet?

Any news from Boeing yet or still all PPRUNE guess work?

I think the assumption is that any wire that got pinched was internal to the ELT, so nothing to do with the airplane wiring. I'm puzzled by this insulation thing, it really didn't look much different from type 44 and the 230V wiring was better (thicker) insulated so no real difference from most airplane wires. I can always be proved wrong of course - it happens a lot! - but as far as this incident is concerned, the ships wiring could be a bit of a red herring.
PVC insulation is not permitted on aircraft, toxic when lit!

It always has been.

The only wiring to and from the ELT is control/data wiring which carrys miliamps of current and is not directly connected to the battery.

If any of these wires were incorrectly connected or short circuit it would cause logic problems for the ELT controller chip but it wouldn't catch on fire.

Quick work by Boeing fitting out a new Rear Fus 'Barrel' for the ET 787 already :ok:

Sort of depends on what the control-data circuit wiring was shorted TO external to the ELT --for example like a 32 vdc bus bar or any power circuit or sneak circuit.

remotely drop a piece of 12 gage or smaller wire across your 12 volt car battery AFTER clearing the area . .