"Self-extinguishing" material stops burning, because it's already burnt part doesn't shed or become porous, blocking oxygen from the non-burnt part underneath it, so the fire is smothered. Think of a fire in your fireplace. When it's about to go out, you take the poker, and knock the burnt part of the wood off, exposing the unburnt part to oxygen, and the fire increases. In self-extinguishing material, the burnt material tends to stay on and block the oxygen, and, there's no one with a poker, knocking the burnt part off.

That is one explanation and the other, closer to the sponsored research, is that, like a candle, with heat applied the material gives of vapours which can burn. Remove the heat source and everything cools to being inert again.

The issue in the 787 case is to detremine what was the initial heat source. If it was the ELT itself then it would be a first. If it was something in that area which then caused the ELT to generate enough heat, maybe. But what if the heat source managed to bring e.g. CFRP material up to the temperature where it and/or other local materials gave off combustible gasses which then sustained the burning and then caused the disruption to the ELT?

FAA to issue AD ?
 

Boeing 787 Dreamliner: FAA to issue 'airworthiness directive' in wake of fire | Business | guardian.co.uk

Boeing 787 Dreamliner: FAA to issue 'airworthiness directive' in wake of fire

Regulator to order mandatory inspections of 787's emergency beacons just two months after lithium-ion battery problems

..
The Federal Aviation Authority was due to order mandatory inspections of the emergency beacons aboard Boeing's ill-fated 787 Dreamliner as early as Monday after a fire broke out aboard one of the planes in London.
The FAA "airworthiness directive" comes just two months after the 787 was certified to fly again following a global grounding triggered by problems with its lithium-ion battery system.
A fire aboard an Ethiopian Airways jet at London's Heathrow airport earlier this month forced the closure of both runways for more than an hour.
The UK's Air Accidents Investigation Branch (AAIB) concluded that the fire started near the aircraft's emergency locator transmitter – a distress beacon used to help rescuers find a plane if, for example, it is forced to land on water or in polar regions. The focus of attention appears to be whether a pinched wire under the battery cover triggered a short circuit.
The FAA spent the weekend telling other aviation safety regulators around the world of its concerns. It is expected to formally issue the directive early this week, possibly as early as Monday.
The beacons, made by Honeywell, are powered by a lithium manganese battery, which could have suffered a short circuit. Last week the FAA said its inspections would call for operators to check "proper wire routing and any signs of wire damage or pinching, as well as inspect the battery compartment for unusual signs of heating or moisture."
Robert Mann, an aviation expert at consultant RW Mann, said it was unclear whether the latest issue was caused by installation, quality control issues or design issues specifically related to the 787. Honeywell had issues with its emergency locators in 2009 that led to the beacons failing to send out signals. But Mann said the issue could also be specific to the Dreamliner.
The 787 is the world's most technologically advanced passenger jet. Its use of lightweight materials means its uses 20% less fuel than its peers. Aluminum wiring and Teflon coating are used to save weight. "We got rid of aluminum wiring in the US in the 1980s because of the tendency of aluminum oxide to cause problems," said Mann. "And there have been reports of fragility with Teflon insulation." ...

The battery box was to meet the new RTCA standard for LiIon batteries, the new Cessna Citation has a similar box and had to have similar tests.

Could be. I think it's a great solution to the problem.... Here's the scenario:

1) Plane flies high in the sky.... Airframe gets very cold....
2) Airframe made of composites has much lower thermal conductivity than aluminium. Nett result... airframe takes longer to get cold on the way up.... once cold... takes longer to warm up on the way down...
3) Plane lands, doors open, passengers get off. Cabin fills with air far more humid that the 15% talked about on this thread.
4) The moist air, inside the aircraft, getting close to the airframe, forms condensation.... Since the airframe is cooler than we see in aluminium airframes.... we see more condensation....
5) Water and electrical circuits don't go too well together...
6) Issues that previously were unlikely to occur, become more likely, in the more moist environment.

So by putting the battery in a sealed box.... nicely ensures that the condensation doesn't get to the battery... It wasn't poorly made batteries, or overcharging.... it was a short caused by the battery being covered in condensation.... Oh and meant to say.... the technology behind the battery wasn't the problem and this is why it didn't make sense to change to conventional batteries...

I could be wrong of course, just a theory.

Not necessarily. Airframe made of composites has much lower thermal capacity as well, so less "coldness" stored in the airframe.
GA experience: Aluminium airframes parked outside have water accumulation inside in the morning, GFRP airframes parked outside do not (or significantly less). Might be an issue of the sandwich construction as well, so for a monolithic dreamliner it may be different again.

Here's a thought: The new battery-box in the 787 is vented to atmosphere, so at altitude it's going to be at low pressure, and maybe quite cold (I don't know if the box is insulated, or how much of the aircraft's warmth will penetrate). On descent the box will "breathe in" the outside air, and if it's humid, will the cold battery have a tendency for condensation to form on it? I also wonder if they had to strengthen the battery's case to withstand the low pressure around it?

An interesting theory...
 

@ simple-simon post #666

but could you condense it down to a simple version?


Looking at the pattern of the charred area it appears that the longitudinal struts (also a composite structure?) shielded the skin or acted as a heat-sink to pull heat out of the surface.

i wonder if the coeff of thermal expansion (CTE) of the composite is much greater than aluminum and may allow more aircraft growth and contraction such that wire chaffing might occur?

You are presuming no overpressure valve or rupture disk in the vent? I don't know either way but would have assumed the opposite. I cant believe those cells would like to spend most of their flying lives at unpressurised Ps & Ts?

It's not.

It is only vented to atmosphere once the pressure inside the box ruptures a disc in the vent. This protection is set to rupture at a much higher pressure than the differential at normal altitude.

Maybe twice as much as aluminium, I am not sure about type of resin:

Aluminium 22.2 . 10-6 m/mK
Epoxy, castings resins & compounds, unfilled 55 . 10-6 m/mK

That means ca 1 mm per 1°C for hole long fuselage. Fuselage is getting shorter at FL so wires are not tighten but some movement surely exists.

2 simple-simon: Interesting hypothesis...

I think you are all reading way too much into this. If they shorted one of the battery leads under the cover, it would only take time to make an ELT immolate.

CFRP thermal expansion?
 

CFRP typically has a very low thermal expansion, at most about 6 times less than Aluminum at 300K. If designed right, it can have almost zero. Many sophisticated structures (that are not limited by weight) use it, despite its cost, to take advantage of this property. If there's any chafing it would probably be because the metal wiring changes size while the composite structure does not.

Your data is wrong.
Thermal coefficient of expansion of CFRP is about 5 times smaller than aluminium. (2.3 e-5 per degC for Al and 0.5 e-5 per degC for CFRP).

Is 'unfilled resin' the right number to use? I thought carbon composite is much better than that - because of the fiber, optical tables made of it have a COE typically 1/10th that of steel for instance, so I thought the number is lower than Al, not higher.

The hugely dominant effect is flexure in flight, have you seen the wings on takeoff?

If condensation is the cause of battery fires, and Boeing "knew it", it can be easily tested in test scenario. Are you suggesting conspiracy that Boeing is trying to hide 787's condensation issue as it effects not just the battery but the entire electrical systems on the 787s (which is a lot), and may even force Boeing to redesign the entire plane?

There are a lot of "ifs" in your statement. I could bet my home that condensation did not play any role here. But even if it did you wouldn't have to redesign electricity - you simply turn down humidity to much lower levels. There is nothing in the design of A/C-ventilation in 787 that says you MUST have higher humidity.

In light of the discussion re: composites and aluminium alloy in the
presence of fire, I wonder if someone (amicus ?) could comment:

In a composite structure, serious fire at one side of the sheet could
cause serious delamination and strength reduction before it burnt through,
due to the insulating properties of the composite materials. Aluminium
alloy, on the other hand, even though thinner, conducts heat very well
and has a high melting temperature.

Seems to me that, in the same way that an aluminium pan doesn't melt when
exposed to a gas flame, so long as it doesn't boil dry, aluminium should
be safer, especially at 30k feet, lots of air cooling the panel and air
temperature of say, -50 C ?...

Wasn't that a selling point of this aircraft to the passengers?

Yes, it was ONE OF selling points. It doesn't mean that higher humidity is mandatory.

syseng68k,
Thank you for your kind request and I trust that I can make a sensible and accurate response to your good self regarding conduction and insulative properties of both aluminum alloys and CFRP, whilst simultaneously attempting to correct some misunderstanding by others and make some suitable, accurate and helpful remarks regarding relevant differentials of Coefficients of Thermal Expansion (CTE) and other composite properties.
First, please let me address those who claim that CFRP quote "chars'" and that it thus self extinguishing. Sadly this is not the case for epoxies, I again repeat to those that will hear, the fact that all epoxies have been banned from aircraft interiors for around the last 30 ears and for excellent reasons, and it was not merely the flammability and combustability of such epoxies, but primarily the Fire, Smoke and Toxicity (FST) emisions that occur.
And, yes, a char develops. but only as a result of the epoxy having first burned with deadly initial combustion, flaming, smoking and emitting copious FST hazardous products in the process. Incidentally, that is what we used to employ way back when to make carbon/carbon, but that process was a controlled, pressurised and in an enclosed chamber. We used phenolics, primarily, as they have a greater carbon yield than evil epoxies. However, even that process , required over seven re-denisification and burn cycles to come close to the desired theoretical density of carbon/carbon.
The epoxy itself,and I have both performed or witnessed many 100's or 1000's of OSU ( Ohio State University) tests as developed back in the 60's re testing flammability of epoxy interiors, seat cushions, fittings,overhead bins and the like which became a semi-standard interior burn test over the decades to prove this point. However, and it's a very large however, the OSU test was designed around a mere burning cigarette or lighted pipe scenario, with a 50 watts level, far from 28V electrical fires and shorts and fuel fed fires in a survivable crash which requires 200-250 watts per square metre and their ilk. This point is cited and detailed in my paper as some have read on this board.
But the charring of epoxies does not, repeat NOT, prevent burn-through which is why the FAA and Boeing developed a whole new set of high wattage burners to try and adequately simulate and test for burning fuel fires and resulted in the FAA, over Boeing's weeping, wailing and lobbying to stipulate that the lower half, and, most regrettably only the lower half, of the 787 fuselage be expensively and heavily insulated with a special anti-burn through insulation to allow a five minute escape window in case of a wheels-up or off runway survivable crash.
However, and here is yet another huge however, the FAA and Boeing still had to assume and design the burn-through test only for a totally intact, all doors closed, no slides deployed no doors opened and no fuselage fractures, given the FST loaded epoxies employed by Boeing. Clearly, in most survivable crashes, this is not the case and I supplied the FAA, Boeing and Airbus with over 150 such commercial airline survivable crashes since the 1980's as my paper cites. All were survivable crashes with fuselage fractures and/or opened doors. The simple and clear fact is that Boeing and the Northwest FAA Office did not have a prayer of certificating the 787 unless an intact and closed fuselage was assumed as a basis for fire testing in the realm of 200-250 watts as is the case in fuel fed fires. Specifically, EADS also presented totally independent, but similar findings re the A350 two or three years ago.
Now , allow me to wander back, please, to the char that some have cited. All such claims are nonsensical, tendentious and worthless twaddle, to put it mildly. A "CHARRED" CFRP is no longer CFRP, it is merely a residue of strands of free CF, either woven or UD, but it is no longer a composite structure capable of meeting any design loads or criteria at all. So 'char' is a silly diversionary tactic , pure and simple,with the emphasis on simple to my mind and has nothing whatsoever to do with any structural load carrying ability or any chance to sustain any pressurisation loads. I hope that I see no more silly inputs re"char"and would note that the non-structural and useless char would be blown away by the 500 plus mph airflow.
Next, please let me outline briefly the relative CTE's regarding Aluminum and CFRP and epoxies. Let me work in old fashioned degrees F units, please. just to humour me.
Typically an aerospace alloy will have a CTE of 12-13 x10 to minus 6 inches/inch /degree F, and epoxy will have (in its pristine state epoxy only state it will have 22-23 in same units). But not in a CFRP composite whose CTE is controlled by the CF with a modulus of 40 MSI vs epoxy at a mere MSI of less than 1.
MSI matters, just as loads follow stiffness (same degree F units,of course). This differential generates internal stresses in the composite, but they are usually of a second order concern, but some of we composite folks like lower cure temperatures to minimise such internal and residual autoclave induced curing stresses. For CF itself, as a unidirectional material, it has an expansion close to zero (typically 1 or less re CTE units quoted, which is why it is employed for space mirrors encountering wide night/day temperature swings. This is also why INVAR is typically used as Boeing and other aerospace companies as tooling material to minimise problems involving thermal distortions. Boeing and others typically employ a quasi-isotropic layup, with, I note, emphasis on the quasi, as there are some significant differences between a true isotropic material and a quasi-isotropic material. Such CFRP structures typically have CTE's in F units of around 3-3.5. I hope that this clarifies and settles the CTE issues previously discussed in this thread.
And, prior to getting to my final points regarding thermal insulative and conductivity properties of aluminum alloys and CFRP's as I promised that the outset of this overly long input, let me give some relevant metallic vs. CFRP cross plied properties for others to mull over. CF is widely touted, and oft over-touted, regarding its strength, but let us be very careful here. A decent CFRP will have a tensile composite strength, if a UD material at 60 % fiber volume, of around 280- 320 KSI,( note, this is the sigma 1-1 equivalent to metallics).
A quasi-isotropic composite in the same CFRP will have a tensile value of around 90-120 KSI. Now, let us look a couple of weaknesses without boring you all with the hygroscopic nature of that nasty epoxy.
The shear strength of metallics is typically 60% of the tensile, so for a decent steel, for example, say in the 240 ksi range we will have a shear strength of around 145 KSI. Now look at composites and up pops that nasty epoxy again. Whereas Steel will have a SBS or ILSS strength of 144 KSI, a quasi-isotropic composite will have an ILSS of 8-10 KSI static on a good day and, if we allow for fatigue et al, we are down in the 4 KSI area. And finally another key nasty is the short transverse tensile strength ( equivalent to metallic sigma 3-3), which is entirely epoxy dependent and no CF failure is involved, there we find on a good day around 3-4 KSI with fatigue knocking that down to around 1-1.5 KSI which is close enough to zero in this composite engineer's mind and no tensile Sigma3-3 asallowed by an decent and competent comosites engineer.
Achilles only had one heel , lucky for him, but for we in composite design and analysis,there are plenty of other heels to fret about. This is not an anti-composite rant of any ilk, but rather to emphasise why composites need to be analysed far differently and much more closely than most metallics Further, large scale repairs become much more demanding and possibly questionable in contrast to the blithe assertions of some posters on this board. And, as a final point,why has nobody in the composites community,after a full half a century of designing and using CFRP, has yet developed "A'" basis allowables for composites as is so common for metallics? Why and we are still operating with "B" basis allowables with significantly lower probabilityand confidence levels?
Now, belatedly back to the original question that I was requested to respond to and, perforce, my final zinger for today for those seeking to minimise the magnitude of the 787's inherent epoxy based FST et al difficulties.
Yes,CFRP is indeed an thermal insulator compared with aluminum alloys, but also exhibits significant differences depending upon fiber orientation and layup. This, in turn, leads fires, heat and the like to be concentrated in one local area rather than with aluminum's high thermal conductivity, which lowers and significantly lowers and dampens peak temperatures in event of fires from whatever the source.
I trust that this helps the ongoing discussion.
And now I promised you a zinger and here it is; for all proclaiming and advocating the efficacy and safety and non -flammable nature of CFRP, let me issue this very simple challenge.Go out and buy (or borrow from your missus or similar)some aluminum frying pan. Then please cook something requiring 600-650 degrees F on a gas stove. Next, just to humour me, reproduce that same test, but this time first build a CFRP frying pan of similar size and construction and cook the same food with 600-650 degrees F gas cooker. There is only one stipulation, as I do not want you or your loved ones or pets to suffer or die in such a foolish attempt, please do this test of your cooking skills on an outdoor barbicue well away from all humans and pets and let me know the results. In closing we all know, I would hope, why there are no CFRP cooking utensils on the market and,just as a clue,it is zero to do with cost and all the do with flammability and FST.
Any takers, 787 defenders and "it only chars and is better than aluminum" folks, please put your frying pan where your mouth is?
Cheers and apologise for such a long post, but I hope is deemed of some value.

Amicus's post is very interesting, I note the Asiana 777 crash at SFO burnt through its upper fuselage, but not the lower, I wonder whether that a/c (777) has any upper insulation.? If composites burn more readily then maybe 787's should?

Maybe the only way to answer these questions on flamability is to take a number of aircraft from the world's 2 principal manufacturers and ignite them simultaneously to see which produces the most toxic smoke and which burns longest.

Airbus - A320 and A330

Boeing - 777 and 787

You've picked the wrong Airbus example, the A330 is mainly metallic. I guess you meant the A350 which is around 50% composite.

Boeing release their Q2 earnings today and have the earnings call at 1530 UK time. Why not call investor relations and ask the question of the executives on the call today?

Fantastic post Amicus, thanks. I will have to read it again to understand it all better, but it does raise serious questions.

Amicus - I've bee reading this:-

Any studies on this from an aerospace perspective?

Coeff of thermal expansion is negative for carbon fibre. Coeff of thermal expansion of the CFRP depends on the layup, it might be negative in one direction and positive in the other one, it might be very close to zero in a balanced layup of fibres in a matrix.
However, a wound fibre fuselage barrel may increase its diameter (fibre direction) in the cold air at altitude, while increasing additionally due to the pressurisation loop stress, so overall diameter increase may be more than the one of an aluminum fuselage. But I seriously doubt that this is a challange for the wiring, it should be designed to withstand airframe deformation.

This is the reason why a composite aircraft structures design should look totally different from a metallic one. Both material types have their superior strengths and their enormous weaknesses. The key to composite deign is to understand this and to design accordingly. For example in a pressurized fuselage skin the loading is almost entirely in-plane, so sigma 3-3 or ILSS is "close enough to zero" to perfectly meet the load carrying capability of a CFRP layup. On the other hand any item loaded in all three dimensions (e.g. a landing gear main fitting) will never be seriously proposed to be made from CFRP. As stated before, composites are more or less artificial wood, the structures design should be fairly the same (except that nails my not be a good idea...). Unfortunately in the large aeroplane world (maunfacturers, operators, authorities) there is little knowledge of wooden aeroplanes, hence there is an awful lot of misconception going on.
Having designed, build, tested to destruction, certified and repaired a CFRP glider wing, I often wonder what those "metal guys" are trying to build from CFRP...

Shirley I'm not the only reader of this thread to have ever burnt a fibreglass moulding on a bonfire?

A bath, a caravan roof , a dinghy and part of a vehicle body all exhibit the same characteristics,as regards burning.

Like any other plastics, lots of thick, black smoke is emitted and the flame front spreads rapidly across the surface, accompanied by a typical "sizzling" as the plastic in the heat-path of the flame-front bursts into tiny, popping bubbles which rapidly burst, releasing their inflammable gases and thus progressing the flame-front.


The plastic (resin) burns away completely, leaving a perfect armature of the original moulding....It is, however, more fragile than an eggshell and will often collapse under it's own weight.
Glass fibre /Carbon-fibre/ Kevlar....it doesn't really matter............................of itself, the fibre is soft and pliable, the resin impregnation gives the strength and rigidity...burn the resin and you've little more than a starched textile.

Many a fibreglass/Composite boat has been burnt to the waterline, I would not like to be in a burning Composite aircraft.
I'd take my chance in something like a Cirrus, but not in a commercial airliner with the mass of attendant electricals, water heaters,pax attempting a crafty puff etc. no, IMO there is a good case for composites in aircraft, but the Pax deserve a more robust survival-cell.
Self-extinguishing resins are readily available,their suitability in this application is another issue and if the flames or loss of strength don't get you, the fumes surely will!
Thanks, Amicus for your highly technical treatise. It leads one to believe the public have been hoodwinked by the vested interests.
The "screamliner" *could* have had a huge economic advantage over a conventional aircraft, albeit with a compromised level of safety.

We all take our chances weighing risk and gain in our daily lives.
Generation 2 of the "Plastic -Fantastics" may well bring the much-vaunted benefits, but I fear the 787 was too many steps too far, too soon.

On the cause ??
 

787 fire investigation looks at pinched battery wiring | Business & Technology | The Seattle Times

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.

Boeing and government investigators now believe the July 12 fire on a 787 Dreamliner at Heathrow Airport in London was likely caused by the incorrect installation of a small lithium ion battery inside an electronic device.
If that’s confirmed, the fire was due to human error, not a Boeing design flaw.
U.K. investigators who examined the device, called an Emergency Locator Transmitter (ELT) and made by Honeywell, found that the internal wires connecting the battery to the ELT had been trapped and pinched when the cover was reattached as the batteries were inserted, according to two sources with knowledge of the matter, one inside Boeing and one outside.
In photos of what was left of the device, “You can clearly see the two wires crossed over each other. It’s quite evident the wires show evidence of being smashed,” one source said.
Installing the battery package entails unscrewing the cover of the relatively small device, dropping the battery pack of five cells into a slot and connecting the two wires that protrude from the battery pack to a receptacle in the ELT.


goes on ...


The two sources suggested that Honeywell might have replaced the batteries at some stage before delivery of the jet because the devices sat on the shelf during the years-long 787 program delays.
If this were correct, it could explain why the accident happened to the 787 in particular.
Investigators are also looking at whether overheating of the batteries as they sat parked in the sun during the four-month grounding of the 787 fleet earlier this year could have led to internal damage that contributed to the failure.
There’s no evidence of moisture damaging the batteries, which had been another theory put forward in the press.

"Self-extinguishing" certainly shouldn't be confused with "fire proof". Self extinguishing materials may stop the spread of fire, but certainly should be replaced at first opportunity. Also, isn't a 777 an aluminum bird? Seems like some think it's a composite.

I can't help but think that equipment designed such that it allows the wires to be crushed when reassembled suffers more from "design flaw" than "human error". There are billions of devices out there that manage perfectly well to have replaceable batteries that cannot suffer from this problem. SOme of them are probably in safety critical applications, too.

Regardless, Boeing can point the finger at Honeywell if blaming the maintainer doesn't stick.

I know I posted this before but relevant to the current comments, this was my all glass fibre aircraft following a crash land (after I sold it luckily)

http://www.funfly.co.uk/images/KISS.jpg

FF

If analysis shows that the damage to the composite fuselage is as structurally significant as it looks from its external appearance, then Boeing would still have some difficult questions to answer; it wouldn't be acceptable for the integrity of the aircraft to be compromised by a single LRU internal short circuit.

Not necessarily.

From an electronic design point of view, some cables are longer than they need to be so that parts can be removed without having to unplug/disconnect one thing from another.

Making a cable short enough to not become trapped in a reassembled casing, can mean having to disconnect it to remove another part of the circuit which may lead to other problems or puts tension on the wire which could lead to a break.

Much better to have a looser wire which allows greater accessibility and an SOP which involves making sure the wire isn't trapped when the device is manufactured.

Remember these beacons have a battery life of 10 years and once installed should need very little or no attention.

What point are you making with this picture?
Are you saying CFRP planes burn more or burn the same and Aluminium alloy aircraft?

I've seen plenty burn out hulks of more traditionally constructed aircraft, large and small.

Sorry mate, not making a point. Just though it might be interesting to see what a burnt out glass fibre aircraft hull looked like as there had been a lot of comment about glass fibre burning.

I see your burnt-out fiberglass light-sport aircraft and raise you three burnt-out aluminum Cessnas and Pipers.

http://www.fiddlersgreen.net/aircraf...crash-fire.jpg

http://wilko.files.wordpress.com/201...plane-fire.jpg

http://aviation-safety.net/photodata...1552Image4.jpg

Of course none of these fires have any relevance to the case at hand, as they are uncertified aircraft (your case) and CAR3 / FAR 23 certified aircraft (my case) which have no requirement to be tested or certified to prevent burn through as FAR 25 aircraft have to be.

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.

Shirley???????????
 

Who is "Shirley"?

Re this quote in the Seattle Times article above: "It’s quite evident the wires show evidence of being smashed,” one source said.

How do you 'smash' a wire? With a brick or a rock or a hammer? Is this just bad English, or a typo? Are we supposed to 'correct' the word into another such as 'mash' or 'crush' or 'pinch' or anything that might make some sense, or is that taking liberties and are we expected to take this word at face value? :ugh: