And stop calling me Shirley....

Sorry could not resist, see the "airplane" movie series for the reference if new to you.

Amicus,

Thanks for the lengthy explanation, though not being a materials engineer,
am having a bit of trouble decoding the acronyms and values as to their
relevance. Would be gratefull if you could provide a bit more background in
terms of the basics...

slacktide:

Hardly the same conditions, is it ?, as in your example, there isn't the
cooling effect of the outside air rushing by at -50C. The aluminium pan on
a gas stove boiling water is a far better analogy. Fact is, composites are a
good heat insulator, so would get little benefit from outside air cooling.
Of course, all bets are off for both materials on the ground, with no
cooling.

If such a minor fire can cause so much trouble and unknown level of material
degradation, one wonders why fire insulation wasn't fitted to the upper half
of the fuselage. One would think that it should have been mandatory with
such a heat sensitive material...

Shirley shom mishtake (that's enough of that. ed) :hmm:

Has anyone seen pictures of the damage to the inside of the aircraft? There's a chance the damage is pretty extensive, because, with the insulating effect of the composite, it won't transfer the heat to the outside, as quickly as aluminum. It's like the difference of holding a hot cup of coffee in a porcelain cup, instead of a tin cup. You could hold the porcelain cup with your hand, but the tin cup, you'd need to use the handle. In other words, an aluminum skin may have burned clean through, where as the composite skin, only showed burn marks on the outside, but didn't burn through. It may look worse on the interior of the plane than we imagine! Also, imagine the fumes, from the burning composite. Yuck!

A Smashing Success
 

i enjoy the attention to precision in the written word--it seems to be primarily a British trait as keepers of the king's english. We are after all two countries separated by a common language.

OT: A crushed pair of battery leads eventually shorted together and generated enough heat to start a fire that has a curious burn pattern--it appears as two charred areas, one forward and one aft of a central region with no burning. What is in the central region that wasn't affected?

Queen's English dear boy! We haven't had a King for a while, though now we've got three lined up!

Kenneth:

...and, curiously, the smashed wires that are said to have caused the fire are still in good enough condition
that the "smashing" is evident. One would expect that such wire would need to be red hot and melt to cause a
fire in an area with what (?) other nearby combustable materials to spread to.

That and the fact that the elt battery has a current limiting fuse in each leg and is in
a sealed enclosure.

Sorry, but i;'m not buying any of this supposition (perhaps a different word
would be better ?) until there's more concrete evidence...

I guess that's why a picture is worth a thousand words. I wish they'd publish some pictures of the beacon in question. Maybe the wires weren't pinched, crushed, or smashed after all? Maybe some high voltage got in those wires/leads and arced through the insulation, like a spark plug wire in a car arcing to ground, during wet weather? That's a high tension lead arcing to earth, for British Pruners, I think.

787 fire investigation looks at pinched battery wiring
 

"Investigators believe the July 12 fire on a 787 Dreamliner at Heathrow was likely caused by incorrect installation of a battery that pinched some wires and caused a short circuit." - Seattle Times

The ELT battery (and for that matter other batteries on-board) should have an internal fuse that will open on an over-current condition preventing this type of incident.

Could the Beacon Be a Red Herring?
 

A heck of a coincidence, but maybe, the beacon wires were already burned, from the first time it was powered up, and the fire in question, just happened to be in the proximity of the beacon, so the investigators saw it and said "Well, there's your problem right there!" I've seen this a lot, troubleshooting electrical, electronic, and other technical problems, over the years. People assume that the first problem they see is the problem they are looking for, but it turns out to be unrelated. Wonder if there's a way to test, with some precision, "how fresh" the burned wire insulation is?

From where? And what is 'high'?

High enough to arc through the insulation! Happens on spark plug wires all the time. Could come from lightening, St Elmo's fire, or static discharge. Doesn't necessarily need to be high current, just high voltage, maybe a few thousands of volts. In a moist environment, not as many thousands, as in a dry environment. There's been talk of the insulation being thin, which makes it even more likely to arc to ground.

Well 'Smashed' is certainly not a precise term to apply to cable / wire. . and in this case where reading between the lines the ELT case was closed with the ?battery? leads out of place you would expect some more precision (crushed, crushed together, flattened, split, nicked, trapped etc.)

(And like the other poster I'd think unless the battery fusing was incorrect, omitted or failed this short circuit should simply have blown the battery protective fuse (s) before the battery could overheat.)

You end up thinking the presumed short set fire to some other component in the ELT and that fire then spread to set the battery off . . except very few professional grade electronic components burn for long or that well in a sealed container. . .

If the fire did originate from the beacon, the cause didn't need to be internal to the beacon. If there were something wrong with the charging voltage, where it was a few volts higher than need be, it could definitely cause a battery, Lithium Ion, or not, to catch fire. A battery is charged at a higher voltage than the battery puts out. A 12 volt car battery might be charged at around 14 volts, but charge it with 20 volts, and it just might explode. I don't know what the supply/charging voltage was to the Honeywell beacon, but if it was supposed to be 30 volts and was 33 volts instead, adjusted wrong, or wrong for some other reason, it could cause a fire or explosion. So the fault not being with the beacon, but with the circuit supplying it.

:ugh::ugh:
It has been stated here numerous times - the ELT battery is not chargeable, ELT is completely stand alone unit, it is sealed and not connected with the rest of the aircraft. There are only two wires going outside of ELT to a switch - so a pilot could turn the antenna ON but 787 (or any other aircraft) doesn't supply ELT with any voltage/current.

Jetstream67, I'm with you on that. That's why I wondered if the beacon were a red herring. We need pictures and more information! How does the NTSB and other investigators expect PPRUNE to help them solve the problem, if they don't give us the information! It's almost as if, they don't care if we help or not! BTW: If you European's had used Aluminum, instead of Aluminium, on your aeroplanes, you wouldn't have needed to resort to composites on Airbus! ...Kidding, of course!

Agree - Everything said to date by the investigators suggests the problem was initially something contained within the ELT case before presumably an exploding Lithium battery punched through the ELT casing and spread the fire (as sadly they do rather easily) . . . . and Coagie it has been said many times it was a Primary i.e. non rechargeable Lithium battery

Olesek, I stand corrected. That makes perfect sense, to not have a charging circuit, since it's battery is good for 10 years. Apologies, too much coffee this morning has made me impulsive! Didn't think it through.

coagie Yep but speling probably not the issue here :)

I referred to the ELT battery as "Lithium Ion", when it's probably just a Lithium battery, like one might use in a camera, or smoke detector. Sorry about that.

Syseng68k, You're right. But, I think, even without fuses, the battery leads, if shorted together or to ground, would probably just melt through, stopping the current flow, before the battery barely got warm to the touch, and in a sealed environment, there wouldn't be enough oxygen to sustain a fire long enough (if one even started inside the ELT), that would burn through the enclosure.

":ugh::ugh:
It has been stated here numerous times - the ELT battery is not chargeable, ELT is completely stand alone unit, it is sealed and not connected with the rest of the aircraft. There are only two wires going outside of ELT to a switch - so a pilot could turn the antenna ON but 787 (or any other aircraft) doesn't supply ELT with any voltage/current. "

Except for 406MHz which also have at least 2 more wires for GPS feeds for position data and a coax cable to an antenna. However yes, you are correct that they are not externally powered.

The just released July 22 issue of Aviation Week & SP has extensive article on the fire. I can't retype the whole article (online version is for separate subscription) but I can quote some parts (page 23):

....Insiders also quietly note that the composite structure held up well to the fire. Compared to conventional aluminium, for which FAA tests have shown burn-through times of 30-60 sec in intense fires, Boeing flame tests exhibited longer burn-through times for sections representative of 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.
The composite repair technique, although expected to be complex and costly, is also likely to be relatively easier that a similarly scaled repair to an aluminium-skinned airframe because no testing or checking will be required to match the ductility of the replaced skin with the surrounding structure. All aluminium aircraft skins are subjected to annealing, a heat treatment which makes them more workable and reduces internal stresses, and skins adjacent to those which have been affected by fire must be checked to evaluate their condition.....

syseng68k
 

If the 'crushed' wire was between the positive terminal and the fuse then there is nothing to stop a dead short to the case.

SoS:
Agreed, but to get a short circuit, you need current flow from one terminal
of the battery to the other. Even if one side were grounded before the fuse,
the other side would still be floating, so no current flow. The battery
case itself will be provide isolation to the battery internals and the elt
electronics won't be grounded to dc anywhere on the pcbs. That is, the case
will be floating w/respect to the elt electronics.

In any case, as someone else noted, even if an internal elt wire did burn
through, it would be over in a second or two and should not have anything like
enough energy to start a fire externally.

Not being just b awkward here, but none of the evidence released to date adds
up and there does seem to be an intentional information blackout...

SNEAKY CIRCUITS ??
 

That would be true IF only about the ELT. But two( or more ) possibilities still exist

1) somewhere in the numerous junction boxes/electrcial load /transfer/boxes and remote switching could be a sneak circuit- by moisture or by abrasion, etc. That would put up to 32 volts from either of two " main" batteries on perhaps the normal isolated cockpit/ data lines to ELT ???

2) early mention of ' sparks" in the A/C unit somewhere- but not clear when. Ground power was connected- but turned off at pad supposedly. IF true that sparks were noticed AFTER ground power disconnected- a whole new story.
IF sparks when connected- then why wasn't it checked out. ( unless there is nothing in check lists for sparks in A/C ??? :uhoh:

Sounds like management blowing roses and not the people actually tasked with the repair. I'd take that bet.

From yesterday's earnings call
 

Got to be honest overall they were pretty unconcerned about this situation and re the repair a specific question was asked :-

Our next question is from Josh Freed with the Associated Press. Please go ahead.

<Q - Josh Freed>

<A - W. James McNerney>

<Q - Josh Freed>

<A - W. James McNerney>

<Q - Josh Freed>

<A - W. James McNerney>

<Q - Josh Freed>: All right. Thank you.

Cappt
 

I started thirty-five years ago in the aircraft maintenance business repairing metal aircraft, the last twenty years I have been increasingly involved in composite repair and in my view the Boeing statement has a good foundation in truth.

To the metalcentric ways of thinking that pervade this business I can see how you might come to this conclusion but the repair techniques required for composite structures are very different and should not be seen from a "this is how we do a metal repair" point of view.

@DWS

Mention of sparks in aircon on post 89 on this thread.

Source is article in Financial Times on the 12th July 2013

syseng68k
 

Sorry, I should have been clearer. The return path is through the damaged battery casing via the ELT casing.

The first announcement we had was that the battery seems to have sustained pre-fire damage and the crushed wire finding came later. Is that still the case?

My statement above was based on a scenario where the crushed wire, from the time of assembly, was a passive and isolated path to the casing until such time as the cell burst and exposed the anode or cathode to the ELT casing. If the crushed wire was the opposite polarity to the part of the battery that had become exposed then, current will flow.

This, of course, assumes that the battery did rupture at some point. As you correctly point out, a crushed wire itself, will not complete the circuit.

Is it possible that what is being reported as a 'wire' could actually be two wires sleeved together and forming the flying lead from the battery pack?

If that is the case then pinching that may be all you need to short the battery. Trouble with that is I can't imagine that there wasn't a fuse within the battery, so it should still be protected against a short circuit.

Assuming the cause was thermal runaway in the lithium battery, and I can't think how else there was enough fuel to keep a fire going long enough to do the damage, then I think we are left with a failure that somehow didn't draw a high enough current to blow the fuse but was high enough to heat the battery fairly significantly.

That, combined with a very hot day, a closed up airplane and the ELT located in the crown could easily have got the battery temperature to over 60 deg C which is all it takes apparently!

Fox News scrawl (apologies) says its the ELB. I think ... Now it's time for sport.


Apologies for iPad posting.

DWS:
Abrasion, loose terminals, crimps or other electrical problem generating
enough heat to cause a fire. I think that's a much more likely scenario, as the
energy density required to set light to the composite would be quite high
(otherwise it has no business being used in a transport a/c) and need to be
sustained for some time to cause what is reported to be major damage, enough
to scorch the outer skin. What materials sustained the fire, once started ?.

The elt batteries are not in that class really, but ok, if we suspend critical
facilities for a moment, what was adjacent to the elt to spread / aggravate
a minor fire into a fairly major one ?. Does anyone have links to a pic of the
elt installation in the a/c, or just a pic of the internals around that area ?.
Would be very helpful to have that...

This shows the interior of Section 47 being fitted:

http://i337.photobucket.com/albums/n...ps396bb1cf.jpg


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

I have posted this picture earlier in the 787 thread.
It shows a brand new spare Lithium battery for a SART (Search And Rescue Transponder). It was not being charged, it was not being discharged, there were no pinched wires and the manufacturer could not explain why it ignited, but it did. The damages to our store room and office was incredible from this small battery, probably 1/3 of the size on an IPERB/ELB. To protect the battery it had a solid end cap screwed on, see the tops of the remaining batteries, this was blown off and the battery went like a projectile around the store room denting fairly strong steel shelfs and leaving scorched painted steel in its wake before it came to rest with enough energy remaining to burn into the protective casing of the battery it is resting against.
These batteries scare me.
Per

http://i1339.photobucket.com/albums/...ps979dbacf.jpg

That looks pretty convincing. Had it ever been dropped / physically abused,
was it a manufacturing defect or what ?. Compared to the size of the bricks,
those batteries look much larger than the elt type. Are they the same type
and chemistry, or for a different application ?. You said transponder and the
elt doesn't transpond.

I guess this must also have been reported to the safety authorities, so what
was their reaction ?...

The batteries were taken straight out of the box and put on shelves, they were airfreighted! to us and we could not find anything wrong with the boxes. We reported the incident to the manufacturer of the SART and sent them the affected battery which they in turn passed on to the battery manufacturer. The only feedback we got was that they could not find any faults. I left the company a few months later, unrelated.
That particular battery is now obsolete so I am unable to find any dimensions or chemical composition data. Happened about 8 years ago.
And yes, this was a RADAR transponder.
Per

Syseng68k
While everyone is hypothesising.... take the report from Ancient Mariner about a "small battery, probably 1/3 of the size on an IPERB/ELB" so scale it up to a much larger battery and put that battery in a strong metal container that has its hermetic seal compromised by crushed power wire(s). The repeated heat from the sun on a hot day expands the metal box and eventually the compromised insulation allows a short while the same heat has already taken the battery to critical temperature. The energy release is inside a hermetically sealed box with the exception of the break caused by the same crushed wire(s). All the exothermic energy that led to Ancient Mariner's battery flying around the room is now focused in a jet through the break in the hermetic seal of the ELT. Effectively the ELT could become a self fuelling blow torch anchored to the crown of the fuselage as the battery goes into thermal runaway.

From Battery fires: keeping the Li-ion caged | Aviation International News

"Thermal runaway can occur when the battery self-heats, which can happen when electrolyte reaches temperatures as low as 158 to 194 degrees F (70 to 90 degrees C), according to the FPRF report. Runaway accelerates quickly at higher temperatures, and the greater the charge in the battery, the faster runaway happens. Temperatures during a runaway can reach 1,110 degrees F (600 degrees C). The battery cells will also experience increased pressure, venting or popping of the cell, possible ignition of cell gases, possible ejection of cell contents and propagation to adjacent cells.According to the FPRF report,

“Venting of isolated small cells (cellphone cells and smaller) seldom results in flame ignition. This is likely due to the limited volumes of vent gases released from these cells–that is, the gases become diluted before ignition can occur. In comparison, ignition of vent gases from 18650 and larger cells [used in some laptops] is fairly common: these cells contain more electrolyte (more fuel), and are usually used in multi-cell battery packs. If the flow of vent gases is ‘restricted’ due to the configuration of a vent port (typical in hard case cells), flames emanating from the cell will be highly directional (flames from 18650 cells are often described as ‘torch-like’)."

My bolding.

That description could explain the damage and the heat in the area of the Ethiopian 787 ELT.

Addition:
A photo of a laptop with a thermal runaway from Lithium-ion Safety Concerns ? Battery University

http://www.batteryuniversity.com/ima...rtone-5b-3.jpg