To Speedbump:

Yes, I have been thinking along the same lines as you, that is what makes this such an interesting case.

I really would love to know how they decided upon this approach. I am especially curious about the "plug from outside" technology. There are many pros to have a plug inserted from inside - especially in an airplane.

Plug from inside would require a sharp angle scarf joint (or something with these pegs, nibs, hooks etc) though, otherwise the material might weaken in the edges, enough to MAYBE compromise the plug enough to make it fail catastrophically. A blunt angle scarf joint (which is, I believe, the case with this plane) could theoretically vibrate the glue enough over time to make it unstable.

Now they plugged it from outside. The theoretical case with the glue still stands but they removed the feature for the plug to "plug itself" into the hole. Speculating here, maybe that is to reduce compression stress on the glue. This would correlate well with the patch from inside that supposedly could reduce the effects of pressurisation (which would cause a tension stress on the glue), thus trying to keep glue properties stable. Just speculation from my side.

Thoughts on this?

Speed bump
 

You make the assumption that the plug would be fitted from the outside, there is no technical reason with a well executed scarf joint that this should be any weaker than the original structure.

There seems to be the assumption on these pages that a scarf joint is weaker than the original structure....... It is not weaker or stronger it is exactly the same.

My preferred option would have been to fit the new section as a plug from the inside as this would be less disruptive to the outside of the aircraft.

All this assumes than there is enough room to get the required surface area to perform a scarf joint.

A and C
I would opt for this too.

That is why it is so interesting to know why Boeing do what they do. There must be a very well thought out reason for their repair technique - I would love to follow that reasoning!

A and C

Indeed perhaps it will be a combination:

1. A scarfed joint with the patch installed as a plug from the inside, and then
2. The 8 inch wide extra strips placed over the scarfed joint on the inside (glued and/or riveted in place to give extra support to the scarfed joint).

That might be a good combination.

However there might be a lot of interference from structure inside the plane (ribs, etc) to make this more challenging.

Speedbump

Re plugs:

I thought the above stated that they are plugging it from the outside. Did I misinterpret the description? "Drop it into the space" etc...

I thought the same. But calling the patch a "plug" kind of indicates that it will be installed from the inside to plug the hole (maybe scarfed).

Presumably the Seattle Times reporter is not an expert on composite repair and we should not read too much into the finer details of what he wrote.

And who knows how accurate his source is anyhow.

Speedbump

Try insert repair!http://images.ibsrv.net/ibsrv/res/sr...ilies/nerd.gif

Looks like the tail has gone back on now.

https://twitter.com/Tartn52/status/4...163008/photo/1

Thanks for the photo; I presume this indicates that the repair has been completed and re-assembly is now underway. I would still like to learn more about the actual repair but time will tell.

Nearly finishedhttp://images.ibsrv.net/ibsrv/res/sr...ies/thumbs.gif

Looking forward to hearing how this repair was finally carried out.

I've said it on here before, but I think this is a great story for Boeing and the 787...a fire that would have destroyed a metal frame, and yet this aircraft is being repaired, and will fly again. CFRP is the way ahead, and Boeing will have learnt even more in developing this fix. Well done to all...:D

Would not a metal frame have dissipated more energy resulting in a lower temperature, when the ELT battery failed? Maybe there would have been no fire and no need for an extensive repair had the a/c been constructed in a conventional way?

metal vs. composite
 

Lemain.
Well said and I completely concur that it would have been a non-event or very minor repair for a metallic as the ELT battery is very small with little energy and I bet we never find out the repair cost either.

Amicus
 

I don't think we have enough data to predict the damage that would have been done to a metal airframe and I would suggest that it would not be the ELT battery that would do the damage but rather the burning of what it sets fire to.

As to the time the repair has taken, it looks to me as if the legal wrangling and getting the logistics sorted has taken longer than fixing the aircraft. I think Boeing have done rather well, after all this is the first major field repair of a large composite airliner being done by a company that is not yet well versed in composite repair techniques and no doubt being hindered by those who know a lot about metal aircraft and very little about composites.

I would very much like to get a look at the repair to see what techniques were used.

Aluminum is one of the best thermal conductor materials, and often employed as a "heat sink" or thermal radiator for power semiconductors. For this reason I'd expect results as described above by Lemain.

Conversely, carbon composites are better thermal insulators, and contain the heat as seen in this 787.

787
 

A and C,
As the auto ignition temperature of the Toray 3900-2 epoxy as used on the 787 is a mere 580 degrees F per FAA tests and the autoignition temperature of aluminum alloys is around 2000 degrees F plus CFRP being and good insulator and aluminum an excellent conductor, I think that we can predict and state with full confidence that the damage of an ELT short and fire would be a whole lot less for metallics and we already have proof of small fires in 787 CFRP sitting at Heathrow.

Reading the DOT/FAA I am reaching an opposite conclusion, specially the executive summary of the results where a comparison to aluminium is made.

I seem to remember that in all the earlier questioning of composite fuselages, it was always emphasised by Boeing that it was not an unknown, that they had done military aircraft fuselages like this, they therefore had all the experience necessary of field operations, they were the experts ..... yadda yadda yadda.

Which is correct ?

WHBM

Military chain of commands is so much shorter (ok, generally speaking...) so it's more "fix this YESTERDAY and that's an order!" (ok, overemphazising on purpose).

Civil aviation has all kinds of "red tape" running all across the world and with an Ethiopian plane on a UK tarmac with a US built airframe, insured by Someone and on top of that a major PR stunt for Boeing, of course it takes time no matter how well prepared the engineers might be.

Once the work started it seems they did pretty well - remember we don't know how extensive it was on the inside. I do believe that composite materials are pretty well understood IF Boeing chooses to use the military knowledge people in the civilian process. I am not at all familiar with Boeing's corporate structure but there are occasions where military and civilian engineers are completely separate within the same company (you know, secret stuff, classified stuff, not allowed to share because of the safety of the nation etc), leading to peculiar gaps in information exchange. This will of course hamper the development of products, mainly on the civilian side because that side is the one that really has to consider price tags.

Now, as for how they actually fixed it, I am a curious beast. Any gossip, loose rumours, uneducated guesses, anything besides the post in Seattle Times? ;-D

Is the repair work complete now? I too am fascinated by all the discussion here but would love to know some solid facts about the damage done and the repair itself; wishful thinking perhaps!