Ethiopean 787 fire at Heathrow

[syseng68k]

slacktide:

This entire argument regarding the autoignition temperature of aluminum and
CFRP is bogus from the beginning as it ignores thermal mass. Place a 2" thick
paper textbook and an empty aluminum beer can in front of a lit propane torch,
and let me know which one burns through first.

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...

[syseng68k]

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

[Coagie]

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!

[kenneth house]

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?

[bartonflyer]

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

[syseng68k]

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...

[Coagie]

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?

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.

[eminencegrise]

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.

[Coagie]

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?

[olasek]

Maybe some high voltage

From where? And what is 'high'?

[Coagie]

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.

[Jetstream67]

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. . .

[Coagie]

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.

[olasek]

So the fault not being with the beacon, but with the circuit supplying it.

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.

[Coagie]

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. . .

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!

[Jetstream67]

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

[Coagie]

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.

[Jetstream67]

coagie Yep but speling probably not the issue here

[Coagie]

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.

[Coagie]

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

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.