ELT
 

fflyingdog.
You are right. There are 2 types. One is attached to fuselage forward of the Fin and another inside the cabin as a portable unit, which the Cabin crew can deploy manually also. This unit is the one located in the overhead bins. Both have LI batteries. Both used for several years. Surprising this had to wait for installation B787 to go up in flames in a dramatic way. :ugh:

Carbon composite repairs
 

Blakmax, spot on!

Repairs, metallic or composite, to commercial aircraft are treated effectively as a modification, and require the same level of approval as the original certification. Repairs that do not meet the same strength standards as the original structure may require an additional maintenance programme, e.g. regular inspections, to assure the repair's continuing integrity.

A couple more possibilities on why Honeywell was invitied to join the investigation, beyond the ELT being under suspicion as a primary factor in the fire.

1: If the ELT has non-volatile memory for maintenance purposes the contents might help in creating a time line and conditions of the incident.

2: I took a look at the first few pages of this thread and see no reports on who discovered and reported the fire.
Theres is one qoute re "sparks in AC unit" but with no information on when in the event that was seen.

Begin pure wild speculation, I realize this is unlikely but stranger things have happend:

Is it possible that the fire burned the insulation on the cockpit activation circuit and triggered the ELT?

Did the fire brigade respond to investigate a possible crash?

Even if as is totally likely the above is not the case the ELT may have been triggered so there could be questions on its performance under fire.

Gliders do use carbon fibre for wing spars since 1972, and have nothing to to with surfboards. Glider do operate carbon fibre to stress levels even above what large aeroplanes do. The only (and probably most relevant) difference is that gliders are typically clean, while large aeroplanes are contaminated by fuel, oil, hydraulic fluid, deeicers... you name it, they are exposed to it. To do a bondes repair to contaminated structures requires extremely throrough cleaning, otherwise it becomes dangerous. Thats why bolted repair is so popular.

TYPICAL ELT
 

for example
https://commerce.honeywell.com/webap...9524&langId=-1

Batteries
 

Non rechargeable Lithium batteries will begin to self combust at well below the 500 degree temperatures reported as necessary to burn the airframe.

It could be hard to decide is a burnt ELT was the primary or a secondary source of combustion . . which may be why there is a bit of a delay


Primary Lithium Cells (Non rechargeable)
　
•Capable of self-ignition (thermal runaway)
•May worsen an independent controllable fire event •Violent release of a flammable electrolyte mixed with molten lithium metal (large pressure pulse)

Is the ELT in the fin integrated with the aerial through the fuselage? I had assumed that it was. I guess there are ELTs in liferafts too (1 each?) - how many are there on a 787?

ELT activation
 

A remotely positioned test switch activates them momentarily to confirm RF output level and antenna operation but generally sends a different signal to an accident signal

To a previous poster : The antenna is generally a flush insulated slot section type cut and bolted into a metal (i.e. RF blocking) airframe . . the same may still be true of composite airframes as they have quite a lot of metal mesh included in them to address lightening strike issues and that might reduce signal strength

Etud Iavia,
There has been three fires in 787 fuselage to date with burn-through in two. This is in less than two years of flying and low flying hours, no risk analysis or fancy statistical stuff needed, 'Just the facts.Ma'am, just the facts" as Jack Webb said. Its obvious and clear that a major safety hazard exists on uninsulated (upper180 degrees including the cabin) and possibly on insulated fuselage (lower 180 degrees) and we don't need strawmen categories either.
Isn't it just an obvious, proven and clear safety hazard?

Wait, so... if anything in contact with the skin of the upper fuselage heats to 300 degrees centigrade (like maybe an overloaded electrical cable run or the aformentioned battery?) the fuselage skin catches fire, and that fire is self sustaining? And if this were to happen in flight for some reason, would the airflow over the fuselage act like a blacksmith's bellows and turn the top rear of the plane into a giant roman candle within a few seconds until the charred remnants disintegrated in flight, showering burning confetti and smoking corpses over a vast area?

Or has somebody tested this and proved that it definitely won't happen like that and that the fire hazard is only relevant in a post crash scenario?

I read somewhere else that actually it would be much better to be in a carbon fibre aircraft than in aluminium one with this sort of ELT battery fire. First of all fire in NOT self-sustaining, carbon fuselage tends to char and therefore blocks further propagation of fire but aluminium loses its tensile strength with temperature much faster, by 500 deg, it lost most of its strength.

Noted. Toray with epoxy 580deg F. That is surprisingly low. If this is correct, I may have some questions.

Amicus,
I think you may be confusing "Flash point" with "Ignition point". Material will ignite at flash point of approx 200C/392F with external influence. Ignition point, will self ignite at 516C/961F if local conditions prevail.

I do however stand to be corrected :ok:

JSP,
Please stand by to be corrected, JSP, please.The 580 degree F is definately the self ignition point, not the flash point, so my original contention stands.
And with some of contributors seeking to defend the indefensible, I note that I am NOT, repeat NOt discussing the CF itself, but am discussing the epoxy FST hazard of the composite.
And to those who so foolishly claim that CFRP "merely chars", they ignore that, prior to charring, the epoxy has already caught fire, releasing copious doses of smoke, cyanide, carbon monoxides and a lot of other FST toxic chemicals which immediately incapacitates or kills both pax and crew.
A simple point to those simple people; "Why have epoxy based composites been banned by the FAA and all other regulatory agencies for aircraft interiors for the past 25 years, having been ordered to be replaced phenolics and various thermoplastics? further to those same folks, go read the PiperAlpha offshore fire reportand subsequent mandating replacement of all epoxy based composites by phenolics. We are talking public safety and lives here, for goodness sake.
Further, to such folks, I would note for the last time that the compressive and ILSS composite values are shot, useless, finished and structurally useless by around 360 degrees F or so (in fact Boeing's engineers worry mightily if temperatures on commercial A/C composites exceed 180- 200 degrees).
From a structural safety aspect you only need to reach 330-350 degrees F for the critical strength properties to be shot and kaput and good bye pax and crew.
Equally, aluminum properties of aerospace alloys grade are pretty well shot at 400 degrees F, however a aluminum alloys have the decency to recover if temperatures decrease and not self ignite until 1960 degrees F or so, this is in strong contrast to the self ignition point of a mere self ignition of 580 degrees F for CFRP. In addition, aluminum is a far, far better conductor than CFRP, hence the local peak temperature is agenerlly far lower in contrast to CFRP which is a thermal insulator, not a conductor as is aluminum, this is a critical difference.
Finally, if composites have exceeded their cure temperature by 20 degrees or so, they do not recover their structural properties as aluminum alloys do, a critical aspect from fire-fighting inside the A/C and flight survival .
I hope that this short lecture from a composites engineer helps a mite and that I do not in future have to say Codswallop so often.

So, Amicus, if there is a point heat source (like say an electrical short or a spontaneous ELT battery fire) that applies 581F to the inside top of the fuselage just ahead of the tail fin, what are you suggesting happens?

1. Toxic smoke & fumes from hot resin start to fill the cabin? OK, so presumably there's a procedure for that...

2. The structure around the point heat source is compromised... OK, not great, going to cost a fortune to fix in due course, but one small patch of structural weakness does not translate to a crash...

3. Will the skin of the aircraft actually catch fire? Will it burn, will it self-sustain in a 200mph wind blast? Can somebody say with the confidence born of having evidence, that it won't happen?

Hi kwh,
There are no procedures other than fire-fighting, but alas, no hazmat, full face masks and oxygen available for the crew for fighting internal FST epoxy generated composite fires as, such FST hazardous and flammable epoxies for interiors were banned by a once useful FAA back in the mid-80's. I had worked on FST since early 70's and it took that long for FAA to issue an epoxy banning edict.
In the interim there were FST fatalities, for example the Airtours 737 as Manchester plus a number of others such as Swissair 111 over Canada, which sadly crashed with all killed, it was an MD-11. I refer you to British AAIB for their reports, there were plenty of others in various countries. Most recently I worked as an expert witness concerning the UPS Dubai crash, a 747-400F. There were others in freight area as regs are either very loose of non existent.
Hope that this helps,

KWH,
You are way and unacceptably off in item 2, kwh, the Ethiopian fire would most certainly have caused a fatal crash for all on board if it occurred in flight. So "Not Great" is an unrealistic conclusion to draw and I am being very charitable.
Re item 3, I see no reason why fire would not burn in flight and I refer you to the Swissair MD-11 for your review.

amicus,
Codswallop


amicus: However, in your paper you state:

Have you since tested a cured, fuselage equivalent thickness panel of T800/3900-2 and confirmed your speculation? Please share!

That aircraft had an aluminium fuselage that suffered complete structural failure aft of the rear spar. The deaths were by and large due to smoke inhalation from a variety of materials, chiefly the synthetic foam in the seats.

The fuel in that case turned out to be the insulation, which turned out to be far more flammable than the FAA's tests indicated. Also, that aircraft hit the water intact - it was the damage to avionics and flight control connections that proved insurmountable.

Boeing never publicly comments during on-going investigations - none of the manufactures do. They are effectively under a gag order from the investigating authority.

They'll release general PR stuff like "Boeing is assisting XYZ in their investigation of this incident", but never statements about what caused the event. That's the job of the investigating authority.