787 Lightning strike issues v FAA

[Grebe]

Looks like another cost-schedule win over safety .Sure glad FAA management backs their people - WAYYYYY back ..:ugh:

https://www.seattletimes.com/business/boeing-aerospace/faa-engineers-objected-to-boeings-removal-of-some-787-lightning-protection-measures/


FAA engineers objected to Boeing’s removal of some 787 lightning protection measures

Dec. 10, 2019 at 5:00 pm Updated Dec. 10, 2019 at 8:00 pm


By
Dominic Gates (https://www.seattletimes.com/author/dominic-gates/)
Seattle Times aerospace reporterLast spring, Federal Aviation Administration (FAA) managers approved removing a key feature of the 787 Dreamliner wing that aimed to protect it in the event of a lightning strike.

Boeing’s design change, which reduces costs for the company and its airline customers, sped through despite firm objections raised by the agency’s own technical experts, who saw an increased risk of an explosion in the fuel tank inside the wing.

That clash will come under scrutiny Wednesday as FAA Administrator Steve Dickson appears before a House committee examining the agency’s regulatory performance in the wake of the two Boeing 737 MAX crashes.

Lightning protection on an airplane like the 787 that’s fabricated largely from carbon composites is more elaborate than on a metal aircraft. When Boeing developed the Dreamliner, it included special measures to protect the wing fuel tank. It sealed each metal fastener in the wing with an insulating cap and embedded copper foil in strips across the carbon wing skin to disperse the current from any lightning strike.

..... goes on with a few good diagrams

[ATC Watcher]

The FAA initially rejected the removal of the foil from the wing on February 22, when its certification office ruled that Boeing had not shown, as regulations required, that the ignition of fuel tank vapor by a lightning strike would be “extremely improbable,” defined in this case as likely to occur no more than three times in a billion flight hours.

By then Boeing had already built about 40 sets of wings without the foil.


This last sentence is also revealing on how some in Boeing view the FAA ...

[SLF3]

Without wishing to start Boeing versus Airbus debate, does the A350 have the foil in the wings?

The question is only because, if the wing construction is broadly similar and EASA / Airbus require it, that is strong evidence that the FAA should have insisted.

[A0283]

With respect to FAA Administrator Steve Dickson ...

I followed two congressional hearings with him, including his confirmation hearing in congress at the time. My take from that was that he said to have a strong 'flying' CV. But responding to congress members' questions (relating to the MAX) he answered that he had no 'design engineering' and no '(design engineering) certification' experience. Possible manufacturing engineering experience was not discussed but it appears he may not have any. The other 'MAX' witnesses did not have any either by the way.

Will be interesting in that light to follow the MAX certification hearing. He will surely have to lean heavily on the knowledge and experience of others.

Boeing has a 'history' with fuel tank explosions. Discussions about those are still going after many years. So 'surprising' that an issue like this, either static or lightning related, is added to that. And would be 'amazing' indeed, from not only a design engineering but also a manufacturing engineering point of view, if they have indeed proceeded to build wings without solid FAA authorisation.

[A0283]

Having just said that ... taking a look at the Hearing Agenda (thanks by the way @Grebe & Seattle Times for referring to that)

Start Quote

Stephen Dickson, Administrator, Federal Aviation Administration, Testimony
Accompanied by
Earl Lawrence, Executive Director, Aircraft Certification Service, FAA,
Matthew Kiefer, Member of the FAA’s Technical Advisory Board,

End quote

[Chris2303]

William E Boeing must be spinning in his grave!

[Grebe]

William E Boeing must be spinning in his grave!
Yep - and if you wired up his grave, Bill allens grave and t wilson grave, you could power all of Seattle - or generate enough to fire up ole sparky for a few recent types . .

[turbidus]

William E Boeing must be spinning in his grave!

Exactly!

I forefronted technology and innovation...Why are we still using cables to control surfaces?!?!?!?!

[Grebe]

Exactly!

I forefronted technology and innovation...Why are we still using cables to control surfaces?!?!?!?!

Because when all electric goes fubar, it will still fly

And when a special EMP warhead goes off within maybe 100 miles- it will still fly

[SLF3]

So does the A350 have lightning protection for the wings?

[Less Hair]

It has metallic foils embedded in the CFRP-structure.
https://www.airbus.com/newsroom/news/en/2013/04/confirming-a350-xwb-safety-with-lightning-strike-evaluations.html
page 21:
https://www.fzt.haw-hamburg.de/pers/Scholz/dglr/hh/text_2007_09_20_A350XWB.pdf

[SLF3]

The sky is black with pigeons coming home to roost.

[GlobalNav]

The sky is black with pigeons coming home to roost.
The sky is falling.

[Takwis]

The sky is falling. That's just pigeon poop.

[tdracer]

The 787 has a copper mesh embedded in the carbon fiber matrix - the wing, fuselage, pretty much everywhere. In addition - due in part to the uncertainties in the lightning characteristics of carbon fiber - they added a metallic copper foil to the inside of the wing skin. Once they had real aircraft structure to test and analyze they were better able to quantify the lightning threat. Then:
In December 2018, SAE revised the zones based on data from reports of more than 1,000 lightning strikes on aircraft. It found that the area aft of the engines — designated Zone 2 when the 787 was certified — was rarely hit, and so changed its classification to Zone 3.
Combined with the zone change around the engine pylon, it was determined the foil was no longer needed, that the copper mesh along with the nitrogen inerting system provided adequate protection against lightning strike.
I worked with Tom Thorson - the FAA specialist quoted in the linked article - and he's reasonably sharp. But he's a Propulsion specialist, not a lightning specialist. I worked some aspects of lightning protection for 20 years, but my lightning knowledge was a small fraction of that what the Boeing (and FAA) lightning experts knew.
I used to say - somewhat joking - that I knew enough about lightning and lightning protection to be dangerous. Based on some of the posts on this thread, it appears ignorance is even more dangerous.

[Grebe]

The 787 has a copper mesh embedded in the carbon fiber matrix - the wing, fuselage, pretty much everywhere. In addition - due in part to the uncertainties in the lightning characteristics of carbon fiber - they added a metallic copper foil to the inside of the wing skin. Once they had real aircraft structure to test and analyze they were better able to quantify the lightning threat. Then:

Combined with the zone change around the engine pylon, it was determined the foil was no longer needed, that the copper mesh along with the nitrogen inerting system provided adequate protection against lightning strike.
I worked with Tom Thorson - the FAA specialist quoted in the linked article - and he's reasonably sharp. But he's a Propulsion specialist, not a lightning specialist. I worked some aspects of lightning protection for 20 years, but my lightning knowledge was a small fraction of that what the Boeing (and FAA) lightning experts knew.
I used to say - somewhat joking - that I knew enough about lightning and lightning protection to be dangerous. Based on some of the posts on this thread, it appears ignorance is even more dangerous.
Good points- but the penetrations of front and rear spars for various metal parts is also a problem, when immersed in fuel and having possible electrical gaps due to not so obvious ground paths. Walt Gillette was very much aware of that kind of issue while working on one of the programs not listed in his bio. . .wuz there ;)

[Bend alot]

The 787 has a copper mesh embedded in the carbon fiber matrix - the wing, fuselage, pretty much everywhere. In addition - due in part to the uncertainties in the lightning characteristics of carbon fiber - they added a metallic copper foil to the inside of the wing skin. Once they had real aircraft structure to test and analyze they were better able to quantify the lightning threat. Then:

Combined with the zone change around the engine pylon, it was determined the foil was no longer needed, that the copper mesh along with the nitrogen inerting system provided adequate protection against lightning strike.
I worked with Tom Thorson - the FAA specialist quoted in the linked article - and he's reasonably sharp. But he's a Propulsion specialist, not a lightning specialist. I worked some aspects of lightning protection for 20 years, but my lightning knowledge was a small fraction of that what the Boeing (and FAA) lightning experts knew.
I used to say - somewhat joking - that I knew enough about lightning and lightning protection to be dangerous. Based on some of the posts on this thread, it appears ignorance is even more dangerous.
tdracer - I think the main issues are how Boeing have been getting to their determinations (how they have been classifying things - optimistically in favour of easy and cheap), that now justify review. Remember 20/20 the MAX would have been grounded, knowing what we know now.

That and the fact Boeing produced and delivered a large number of aircraft prior to having this change approved by the Regulator/s.

Personally I can see no justification for this change based on "over 1,000" lightning strikes, I would need to see a few more zeros.

[tdracer]

If metal foil external to the carbon fiber structure is so important, why isn't it needed on the A350? According to what Less Hair posted, they embed copper mesh - just like Boeing - no mention of external foil in the fuel tanks...

[tdracer]

tdracer - I think the main issues are how Boeing have been getting to their determinations (how they have been classifying things - optimistically in favour of easy and cheap), that now justify review. Remember 20/20 the MAX would have been grounded, knowing what we know now.

That and the fact Boeing produced and delivered a large number of aircraft prior to having this change approved by the Regulator/s.

Personally I can see no justification for this change based on "over 1,000" lightning strikes, I would need to see a few more zeros.

Boeing didn't do the determination - an industry group (the SAE) did.
When it comes to specialties like Lightning protection, the FAA (and EASA) have long leaned on the expertise of the airframer experts for the simple reason that the regulators lacked that same level of expertise. When I had meetings with the FAA on lightning/HIRF issues, the FAA had one person in the entire FAA who had a similar level of understanding as the Boeing experts - he was designated a 'National Resource Specialist' (I suspect he's retired by now - he was quite a bit older than me, hopefully replaced by someone of similar expertise). The FAA routinely delegated HIRF/Lightning compliance to Boeing - long before Boeing became an ODA - for the simple reason the Boeing specialist knew far more about it than the FAA people.
If the FAA lightning specialist stands up and says it's not safe, I'll take notice. Tom Thorson - as I said a reasonably bright engineer - is not an lightning specialist. He covers all aspects of Propulsion and simply cannot be expected to also be a lightning specialist.
Oh, and aircraft were produced - NOT DELIVERED - before it was approved. Incorporating a change in production before it's certified is quite common - so long as there is a reasonable expectation that it will in fact be certified.

[Grebe]

If metal foil external to the carbon fiber structure is so important, why isn't it needed on the A350? According to what Less Hair posted, they embed copper mesh - just like Boeing - no mention of external foil in the fuel tanks...

RE external foil and embedded copper/composite issues in the fuel tank(s). The problem is that to ensure non spark the copper foil/plate must be electrically continuous between inside to outside AND the internal mesh. ONE way to do that involves copper plating of the composite around the penetrations such that it is similar to a internal-external " gasket " AND electrically continuous to the ' embedded " mesh or foil. A bit of searching on patents assigned to Boeing in the mid to late 80's can explain the details. June 14, 1988 # 4,750,981 is a start.

[Bend alot]

The numbers really do not add up for aircraft to to have not been delivered - that is a massive amount of stock to be holding, but it might be true.

I also think in the last hearing it was said that aircraft were delivered.

This from Tom.

In June, FAA safety engineer Thomas Thorson, concerned that his agency was hurriedly approving Boeing’s desired changes, formally objected.

“I do not agree that delivery schedules should influence our safety decisions and areas of safety critical findings, nor is this consistent with our safety principles,” Thorson wrote, adding the agency’s technical experts had discovered errors in the way Boeing summed up the various risks of the lightning protection features and that with the removal of the foil “the fuel tank ignition threat … cannot be shown extremely improbable”.

Thorson estimated that if the methodology was corrected, the ignition risk “would be classified as potentially unsafe”

[tdracer]

The numbers really do not add up for aircraft to to have not been delivered - that is a massive amount of stock to be holding, but it might be true.

I also think in the last hearing it was said that aircraft were delivered.

Thorson estimated that if the methodology was corrected, the ignition risk “would be classified as potentially unsafe”

40 wing sets is less than three months production. Given wings and aircraft in assembly, units in inventory and transit (the wings are built in Japan), and completed aircraft going through pre-delivery processing, 40 is far from "massive". Further, delivery pre-cert would be a major escape - the sort of thing that gets production shutdown and it wouldn't be a rumor.

"Thorson estimated" - so a non-lightning specialist, with only a passing knowledge of the methodology in question, estimated. Hardly a convincing argument that the aircraft are unsafe.

[Bend alot]

40 wing sets is less than three months production. Given wings and aircraft in assembly, units in inventory and transit (the wings are built in Japan), and completed aircraft going through pre-delivery processing, 40 is far from "massive". Further, delivery pre-cert would be a major escape - the sort of thing that gets production shutdown and it wouldn't be a rumor.

"Thorson estimated" - so a non-lightning specialist, with only a passing knowledge of the methodology in question, estimated. Hardly a convincing argument that the aircraft are unsafe.
There will be no more than 12 in the production line as the maximum delivery was around that amount - 145 deliveries in a year.

So we have 28 wing sets waiting around?

Given the fact of the size of the wings built in a location far from assemble area, a smart and cost cutting company will be holding low stock levels.

Delivery times for the 787's wings, built in Japan, will be reduced from around 30 days to just over eight hours with the 747 LCF. from wikki.

Realistically anything over 30 days stock would be excessive.

Your words on Thorsen gave him credit for being intelligent - so given facts, he could see what classification the data presented should fall into.
The data presented did not meet the classification Boeing gave it, the same thing happened with the MAX and MCAS.

The wrong classification was given.

Thorson wrote, adding the agency’s technical experts had discovered errors in the way Boeing summed up the various risks.

"Further, delivery pre-cert would be a major escape - the sort of thing that gets production shutdown and it wouldn't be a rumor." Again missing required AOA warning on the MAX as to Boeings concern of any shutdown happening from FAA ever.

A year ago many of us would ever have given a thought of Boeing ever doing such a blatant and illegal act, that has changed to highly probable.

[Dave Therhino]

[QUOTE=tdracer;10639358]The 787 has a copper mesh embedded in the carbon fiber matrix - the wing, fuselage, pretty much everywhere. In addition - due in part to the uncertainties in the lightning characteristics of carbon fiber - they added a metallic copper foil to the inside of the wing skin. Once they had real aircraft structure to test and analyze they were better able to quantify the lightning threat. /QUOTE]

There is no copper mesh in the 787 wing composite panels. You might be remembering some of the early design concepts that were discussed, but the final design has no copper mesh. The foil was on the outside surface in strips along the fastener rows, not on the inside, and was there to reduce the current driven through a fastener if lightning attached to or near that fastener. It provided a fail safe feature such that, if one of the other fastener features deteriorated or was left out in production, they still avoided an ignition source. They eliminated the foil because it was so troublesome to repair following a lightning strike, and they were willing to eliminate fail-safety in the design. The FAA staff objected to that.

Airbus doesn't have foil because they have copper mesh, which is pretty much the industry standard.

It's not at all fair for you to label Tom Thorson "reasonably sharp" as though you are much more intelligent than he is. His role is completely different from what yours was. He has to cover over a dozen different propulsion technical disciplines and their applicable regulatory and policy requirements, and he is knowledgeable in every one of them to an impressive depth. He also has working knowledge of airframe structural requirements, airplane performance requirements, systems requirements, structured system safety analysis, and environmental noise and emissions requirements. He is extremely hard working and dedicated. He worked on the space shuttle propulsion system before he worked for Boeing and later the FAA. You worked in a much narrower area for 35 years and became a deep expert in that area. I always respected your intelligence, knowledge, skills, and judgment, but don't damn Tom with faint praise. He has knowledge and experience in areas you aren't aware of. He's also very reserved and doesn't say much until he's sure about what he's saying. "Reasonably sharp" does not do him justice.

[UltraFan]

A question to the physicists among us. I keep hearing that Boeing and Airbus had to do some serious rethinking of lightning protection because the composite structure doesn't form the Faraday cage that the aluminium fuselage forms. It is my understanding, however, that carbon fibre is excellent conductor. And I can actually concur - the cores of my HD leads are made of it. Hence the aircraft structure made of carbon fibre reinforced composite should be a perfect conductor. So what exactly is the problem there? Carbon fibre doesn't form a Faraday cage? Or is that it's too good a conductor? Could someone please explain?

[GordonR_Cape]

A question to the physicists among us. I keep hearing that Boeing and Airbus had to do some serious rethinking of lightning protection because the composite structure doesn't form the Faraday cage that the aluminium fuselage forms. It is my understanding, however, that carbon fibre is excellent conductor. And I can actually concur - the cores of my HD leads are made of it. Hence the aircraft structure made of carbon fibre reinforced composite should be a perfect conductor. So what exactly is the problem there? Carbon fibre doesn't form a Faraday cage? Or is that it's too good a conductor? Could someone please explain?

Short answer: The fibers in carbon composite are not continuous, but embedded in a non-conducting polymer matrix.

[tdracer]

There will be no more than 12 in the production line as the maximum delivery was around that amount - 145 deliveries in a year.

So we have 28 wing sets waiting around?

Given the fact of the size of the wings built in a location far from assemble area, a smart and cost cutting company will be holding low stock levels.

Delivery times for the 787's wings, built in Japan, will be reduced from around 30 days to just over eight hours with the 747 LCF. from wikki.

Realistically anything over 30 days stock would be excessive.


OK, let's do some math. 787 production rate is 14 aircraft per month - split evenly between Everett and Charleston. At any particular time, there are 7-8 aircraft in various stages of final assembly - at each line. So between Everett and Charleston that's 14 - 16 wing sets. Once they push a new 787 out the door, it's far from ready for delivery - it has to be painted, go through various functional tests and fueling/defueling checks, production acceptance flight tests, customer acceptance flight tests, and the actual ticketing and delivery. While I've heard of this taking as little as two week, four to six weeks from rollout to delivery is more typical. Last time I overlooked the Everett flight line, there were at least 12 787s parked there. I've not seen the Charleston flightline, but I have no reason to expect it would be much different, so that's around another 24 aircraft. Add it up and we're looking at 38-40 wing sets - without accounting for any inventory, wings currently being produced, or units in transit. In fact, 40 shipsets is right about where I'd expect it to become an delivery issue if the change wasn't certified. Which, interestingly, is pretty much what's described in the linked article.

Dave, sorry if referring to Tom as "reasonably sharp" came across as condescending or insulting - that certainly was not my intent and I apologize if it came across that way. Tom is very competent (unlike a few other FAA types I dealt with) - my point being he's a Propulsion specialist, which in itself covers a wide range of issues. You can't expect him to be an expert at lightning as well. That's why Boeing has an EMI/Lightning group made up of experts in the field that support the various other disciplines so that they don't need to be EMI/Lightning experts.

Are you sure about the lack of copper in the 787 carbon fiber matrix? Because that's certainly contrary to what I was told by my co-workers who were on the 787 program. It also creates lightning concerns unrelated to fuel tank ignition. While carbon structure is a reasonably good conductor, it's electrical resistance is still an order of magnitude worse than aluminum structure - which greatly increases the induced voltages/currents on the aircraft wiring when a lightning strike passes through the surrounding structure - so copper was added to lower the electrical resistance and keep the induced levels reasonable. I know the the systems on the 787 were certified for higher lightning transients relative to primarily aluminum aircraft (such as 777 and 747-8), but those levels were still lower than what would have been required if it was pure carbon without any additional conductive material added to the matrix.

[archae86]

There will be no more than 12 in the production line as the maximum delivery was around that amount - 145 deliveries in a year.

So we have 28 wing sets waiting around?

Given the fact of the size of the wings built in a location far from assemble area, a smart and cost cutting company will be holding low stock levels.

Delivery times for the 787's wings, built in Japan, will be reduced from around 30 days to just over eight hours with the 747 LCF. from wikki.

Realistically anything over 30 days stock would be excessive.

I don't know on what date the spreadsheet was updated, nor do I know the author's sources, but believe him to have been publishing reasonably accurate 787 data for years.

Uresh, publishing at All Things 787 (http://nyc787.********.com/)
The lines of the spreadsheet of relevance to this discussion which show non-zero entries as of the update are:

11 Undergoing final Assembly
7 Pre-flight prep
16 production testing
5 ready for delivery

That does not cover the pipeline back before actual final assembly, but that pipeline is nothing like a few hours in length. (I used to work in a different line of high-tech manufacturing).

[Bend alot]

OK, let's do some math. 787 production rate is 14 aircraft per month - Once they push a new 787 out the door, it's far from ready for delivery - it has to be painted, go through various functional tests and fueling/defueling checks, production acceptance flight tests, customer acceptance flight tests, and the actual ticketing and delivery. While I've heard of this taking as little as two week, four to six weeks from rollout to delivery is more typical.


Two weeks will also need to be as typical as six weeks, not an exception to equal 14 deliveries.

[Bend alot]

I don't know on what date the spreadsheet was updated, nor do I know the author's sources, but believe him to have been publishing reasonably accurate 787 data for years.

Uresh, publishing at All Things 787 (http://nyc787.********.com/)
The lines of the spreadsheet of relevance to this discussion which show non-zero entries as of the update are:

11 Undergoing final Assembly
7 Pre-flight prep
16 production testing
5 ready for delivery

That does not cover the pipeline back before actual final assembly, but that pipeline is nothing like a few hours in length. (I used to work in a different line of high-tech manufacturing).
The link did not work for me.

The ready for delivery of 5 I assume is over both plants?

[archae86]

The link did not work for me.

The ready for delivery of 5 I assume is over both plants?
Sorry about the link--I don't seem to know how to get the site software not to mangle it. I actually used the editing command to insert a link, and at the time I did so it showed appropriate text for both the display text and the actual URL. But that is not what the site posted in my name.

You may find that simply typing:
All Things 787
Into a browser will show you the place which is published at a location the PPrune site software censors for me, which includes the components "blog" and "spot".

Each of the numbers shown is summed over the two final assembly locations--so yes to your question.

[Grebe]

OK, let's do some math. 787 production rate is 14 aircraft per month - split evenly between Everett and Charleston. At any particular time, there are 7-8 aircraft in various stages of final assembly - at each line. So between Everett and Charleston that's 14 - 16 wing sets. Once they push a new 787 out the door, it's far from ready for delivery - it has to be painted, go through various functional tests and fueling/defueling checks, production acceptance flight tests, customer acceptance flight tests, and the actual ticketing and delivery. While I've heard of this taking as little as two week, four to six weeks from rollout to delivery is more typical. Last time I overlooked the Everett flight line, there were at least 12 787s parked there. I've not seen the Charleston flightline, but I have no reason to expect it would be much different, so that's around another 24 aircraft. Add it up and we're looking at 38-40 wing sets - without accounting for any inventory, wings currently being produced, or units in transit. In fact, 40 shipsets is right about where I'd expect it to become an delivery issue if the change wasn't certified. Which, interestingly, is pretty much what's described in the linked article.

Dave, sorry if referring to Tom as "reasonably sharp" came across as condescending or insulting - that certainly was not my intent and I apologize if it came across that way. Tom is very competent (unlike a few other FAA types I dealt with) - my point being he's a Propulsion specialist, which in itself covers a wide range of issues. You can't expect him to be an expert at lightning as well. That's why Boeing has an EMI/Lightning group made up of experts in the field that support the various other disciplines so that they don't need to be EMI/Lightning experts.

Are you sure about the lack of copper in the 787 carbon fiber matrix? Because that's certainly contrary to what I was told by my co-workers who were on the 787 program. It also creates lightning concerns unrelated to fuel tank ignition. While carbon structure is a reasonably good conductor, it's electrical resistance is still an order of magnitude worse than aluminum structure - which greatly increases the induced voltages/currents on the aircraft wiring when a lightning strike passes through the surrounding structure - so copper was added to lower the electrical resistance and keep the induced levels reasonable. I know the the systems on the 787 were certified for higher lightning transients relative to primarily aluminum aircraft (such as 777 and 747-8), but those levels were still lower than what would have been required if it was pure carbon without any additional conductive material added to the matrix.
TDracer- perhaps part of the confusion comes from dates of changes in the production process such that both answers regarding copper mesh and conduction and lightning strikes are ' correct'

The Seattle Times: Business & Technology: Building the 787 | When lightning strikes (http://old.seattletimes.com/html/businesstechnology/2002844619_boeing05.html)

Is a great explanation as to what WAS about 12 years ago.
this partial quote from the article re Walt Gillette is a great summary as it applied THEN.

Engineers in Everett are debating the best way to achieve that outcome for a largely plastic airframe. In November, one top safety-engineering team expressed serious concern.

That team's internal review, obtained by The Seattle Times, concluded: "It cannot be shown that the current wing-lightning-protection approach will preclude ignition sources in the fuel tank."

Walt Gillette, who leads the 787 engineering team as Boeing's vice president of airplane development, said the review was part of a healthy internal debate that ultimately assures the best engineering solution.

Composites are not new in commercial aviation, he said. And although the safety team's conclusion was "absolutely true at the time" it was written, he said, by the end of the testing and analysis now in progress, the 787 will meet strict Federal Aviation Authority (FAA) requirements. . . . , , , Typically, a bolt moves backward across a wing or fuselage before the charge exits to the ground milliseconds later. At the point of entry on a metal skin, the aluminum can melt, leaving a pitted surface or a small hole.

"You can't hit aluminum with 200,000 amps and expect nothing to happen," Gillette said. "But it's not a safety-of-flight issue."

On the composite fuselage of the 787 a strike is unlikely to penetrate more than the outer layers of carbon fiber.

Such damage needs repair but is not a big deal. More serious is the possibility that the electric charge passing through the airplane will create a spark inside the wing, potentially causing a fuel-tank explosion and destroying the aircraft.

. . . Gillette said his team is perhaps only months away from agreeing with the FAA on an overall 787 certification plan, which will include proving that the risk of a lightning-induced fuel-tank explosion is less than one in a billion.

"When it's all done, the end of a five-year process ... the FAA will evaluate all that we have done," Gillette said, "and they will find that we have met the rule."



Of course that was THEN - Walt has since retired.

There were similar problems on the B2- as to level of protection- and Walt was there. And from memory and not classified, ALL of the B2 was rated at the highest level of protection.

[tdracer]

Two weeks will also need to be as typical as six weeks, not an exception to equal 14 deliveries.

Your assumption is flawed. Production rate does not equal delivery rate over the short term. The production rate is reasonably constant month to month, for what should be obvious reasons. Delivery rate varies dramatically month to month for a variety of reasons. A major reason is that operators tend to want to take delivery at certain times of year - such as right before the big summer season, and not want to take delivery in the middle of the winter when traffic is slow (their own version of 'just in time' supply). Since it's not feasible to produce 8 aircraft one month, and 20 the next, they do what's known as 'build ahead' - the aircraft are tested and prepped for delivery, then parked for a month or more until the operator is ready to take delivery.

[swh]

If metal foil external to the carbon fiber structure is so important, why isn't it needed on the A350? According to what Less Hair posted, they embed copper mesh - just like Boeing - no mention of external foil in the fuel tanks...

Remember the jokes 30 years ago when people would boast that they flew a metallic Boeing, and Airbus builds plastic aircraft ? Like it or not Airbus does have more extensive in service experience with composite aero structures in commercial aviation.

Airbus addressed these issues from the outset in the initial design testing and certification (they actually subjected a test airframe to numerous lighting strikes in the fuel tank area) to and has not changed the way to builds the wings. There is detail design differences between the way the two companies addressed the issues. The A350 wing was designed with the experience they had developed on the A380 HTP and the A400 wing.

The issue here is that Boeing went off reservation and starting building wings that did not conform to the original certification basis without first getting the new certification basis. This represents issues with the production certificate as well as the type certificate.

This is the second production certificate issue I have heard in a week, the other being a 737 wing part identified by the subcontractor as being non conforming ending up on assembled civil and military airframes.

[Dave Therhino]

Dave, sorry if referring to Tom as "reasonably sharp" came across as condescending or insulting - that certainly was not my intent and I apologize if it came across that way. Tom is very competent (unlike a few other FAA types I dealt with) - my point being he's a Propulsion specialist, which in itself covers a wide range of issues. You can't expect him to be an expert at lightning as well. That's why Boeing has an EMI/Lightning group made up of experts in the field that support the various other disciplines so that they don't need to be EMI/Lightning experts.

Are you sure about the lack of copper in the 787 carbon fiber matrix? .

Thanks for the further comment about Tom.

Yes I'm sure about no mesh in the wing skins. I know mesh was seriously considered and I believe it was part of the planned configuration for some time, but I believe concerns about delaminations and difficult repairs after lightning attachments led to the decision to go without mesh.

[Bend alot]

Your assumption is flawed. Production rate does not equal delivery rate over the short term. The production rate is reasonably constant month to month, for what should be obvious reasons. Delivery rate varies dramatically month to month for a variety of reasons. A major reason is that operators tend to want to take delivery at certain times of year - such as right before the big summer season, and not want to take delivery in the middle of the winter when traffic is slow (their own version of 'just in time' supply). Since it's not feasible to produce 8 aircraft one month, and 20 the next, they do what's known as 'build ahead' - the aircraft are tested and prepped for delivery, then parked for a month or more until the operator is ready to take delivery.
So you will agree aircraft ready for delivery are fully complete and signed off ready for service?

Or there is more to be done, such as certification to fly or export?

Current documented (I did not access the above) was 5 units of the "build ahead" over both plants - you implied that had grown to 12 in one plant from your observation and assumed it was 24ish over both plants.

Well we now know why the cut in deliveries was announced - too much stock on hand..

[Grebe]

How did we get from lightning strike issues to a discussion of factory firing (assembly) rates, stations, schedules , delivery rates, sales, financing, shoulda rates, coulda rates, and how many angels on the head of a pin ? :*

[asw28-866]

Grebe, PPRune first law of threading:

Coefficient(Thread Drift) = 1/(Airbus or Boeing) * (Posts Squared) * Contributors

[matkat]

Without wishing to start Boeing versus Airbus debate, does the A350 have the foil in the wings?

The question is only because, if the wing construction is broadly similar and EASA / Airbus require it, that is strong evidence that the FAA should have insisted.
Yes it does, it(The A350) has copper sandwiches embedded in the CRP wing.

[turbidus]

"According to statistics published by the Royal Canadian Air Force, a plane can be struck by lightning on average every 1,000 to 3,000 flight hours. For commercial aircraft, that’s equivalent to one strike per aircraft per year.

Although The Boeing Co. (Chicago, Ill.) has reported that the probability of a worst-case strike could be as infrequent as once every 10 to 15 years, aircraft designs must be able to withstand such a strike.

Boeing recently reported in its AERO magazine that an airplane flies farther than its own length in the time it takes a strike to begin and end. Therefore, the entry point will change as the charge reattaches to other locations aft of the initial point. This can result in multiple burn areas or other damage that could have a direct effect on a plane’s structural integrity, and indirect effects that include damage to radio equipment and avionics or other electrically operated mechanisms, such as fuel valves when electrical potential differences or magnetic effects cause transient voltage spikes. Further, fatal accidents have occurred when current has arced around metal fasteners and ignited fuel vapors."

From my experience, I have been banged at least once a year if not more....so once a year is very conservative, and I think it is more often. Boeing claiming WORST CASE STRIKE (WTF does that mean??) is once every 10 to 15 years??? That has NOT been my experience.

IF the 787 is designed for a once in 15 year strike, there may be some valid concerns...

https://www.compositesworld.com/articles/lightning-strike-protection-strategies-for-composite-aircraft

[svhar]

25 years and 15.000 hours, I never had a strike. It depends of course where in the world your main playground is.

[tdracer]

From my experience, I have been banged at least once a year if not more....so once a year is very conservative, and I think it is more often. Boeing claiming WORST CASE STRIKE (WTF does that mean??) is once every 10 to 15 years??? That has NOT been my experience.


The once/year average for a commercial aircraft is a standard industry assumption. Obviously it depends where you fly and when, and how hard you try to avoid that type of weather. Lightning is a somewhat random event, and just like snowflakes, every lightning strike is different. Some are big, some are small (as defined by peak voltage, amperage, and time factor of the strike), and a small number are massive. Attachment points, while predictable, are also somewhat random which makes a difference in how they affect the aircraft. Most lightning strikes are pretty much non-events - no adverse effects or aircraft damage - but not all.
Although not talked about much, it's simply not possible to completely protect from adverse lightning effects. For example, there have been documented cases where the pressure/temperature shock from a direct attachment to the inlet caused the engine to surge and flameout (CFM56-3/737-3/4/500). There was also a case back in the late 1990s where a 757 took a massive strike to the nose - the induced electromagnetic effects were so strong around the flight deck that it incapacitated one pilot and affected the other pilot - although not enough to incapacitate - so they landed safely and the pilots both recovered fully from the affects. Hence the importance of avoidance whenever practical.

[physicus]

UltraFan Pure carbon fibre is a good conductor indeed, but as GordonR_Cape points out, this only works if the CF is bonded at a molecular level. CF in that state is also extremely brittle, which is why it usually has to be embedded in a polymer matrix. But then there's no guarantee the fibres are in sufficient electrical contact to conduct well. The other factor that's terrible for lightning strikes into a CF panel is its thermal dissipation properties are woeful. The impact site of a lightning strike gets very hot very quickly. If that site can't conduct heat away from the impact site, the spot damage is far worse than on a thermally permissive material such as aluminium. I suspect this latter aspect isn't helped greatly by a copper mesh in the skin, but the conductive aspects most certainly are.

[Dave Therhino]

"According to statistics published by the Royal Canadian Air Force, a plane can be struck by lightning on average every 1,000 to 3,000 flight hours. For commercial aircraft, that’s equivalent to one strike per aircraft per year.

Although The Boeing Co. (Chicago, Ill.) has reported that the probability of a worst-case strike could be as infrequent as once every 10 to 15 years, aircraft designs must be able to withstand such a strike.

Boeing recently reported in its AERO magazine that an airplane flies farther than its own length in the time it takes a strike to begin and end. Therefore, the entry point will change as the charge reattaches to other locations aft of the initial point. This can result in multiple burn areas or other damage that could have a direct effect on a plane’s structural integrity, and indirect effects that include damage to radio equipment and avionics or other electrically operated mechanisms, such as fuel valves when electrical potential differences or magnetic effects cause transient voltage spikes. Further, fatal accidents have occurred when current has arced around metal fasteners and ignited fuel vapors."

From my experience, I have been banged at least once a year if not more....so once a year is very conservative, and I think it is more often. Boeing claiming WORST CASE STRIKE (WTF does that mean??) is once every 10 to 15 years??? That has NOT been my experience.

IF the 787 is designed for a once in 15 year strike, there may be some valid concerns...

https://www.compositesworld.com/articles/lightning-strike-protection-strategies-for-composite-aircraft

It sounds like you are misunderstanding what Boeing was saying. They meant that the average rate of maximum amplitude lightning strikes (probably defined a those strikes with a peak current level in the top 5% of the range of initial return stroke peak current levels (roughly 100 kiloamps and above) is about once every 15 years per aircraft. The rough once per year rate experience you cited for noticeable lightning attachments (which includes strikes with peak currents well below 100kA) is consistent with the threat model used by industry in certification. Boeing was saying they attempt to design for the highest peak current levels in the accepted industry threat model, even though such a severe strike is only expected once every 15 years on average per airplane.

[tdracer]

It sounds like you are misunderstanding what Boeing was saying. They meant that the average rate of maximum amplitude lightning strikes (probably defined a those strikes with a peak current level in the top 5% of the range of initial return stroke peak current levels (roughly 100 kiloamps and above) is about once every 15 years per aircraft. The rough once per year rate experience you cited for noticeable lightning attachments (which includes strikes with peak currents well below 100kA) is consistent with the threat model used by industry in certification. Boeing was saying they attempt to design for the highest peak current levels in the accepted industry threat model, even though such a severe strike is only expected once every 15 years on average per airplane.

Dave, I don't think the 'once every 15 years' rate is per aircraft, I think it's for the entire fleet (wouldn't swear to it though - going back to the 'I know enough about Lightning/EMI to be dangerous). But really bad lightning strikes are quite rare.

[Dave Therhino]

Hi TD. I'm not positive, but I'm pretty sure that would be "once every fifteen years per aircraft," or about once every 50,000 flight hours, as opposed to once every 50,000,000 hours if it was once every fifteen years for a fleet of 1000 airplanes for strikes near 100kA and above. I could be wrong. I don't know that aspect of the industry data either, but I know someone who does. I'll ask him and report back.

[blind pew]

Had three that I remember that damaged the aircraft and a couple that just involved inspections.
Damage was to radome with a few scorch marks.
10,000 hours over 23 years flying for european legacy carriers.
Worst was on approach into Sophia and a couple were between Zrh and Gva.

[Thruster763]

I'm very surprised to hear Boeing do not have any copper mesh in CRP in the wing over a fuel tank or flammable fluid leakage zone. Just because it is zone 3 does not meant it can't have a swept (or even direct) lightning attachment. I would have to be a pretty thick panel not to get to ignition temperature (200deg C) on the underside from a 100kA strike. The regulators have even started to question established guidelines for metal skin thickness to provide lightning protection. The Lightning ARC report makes an interesting read.
https://www.faa.gov/regulations_policies/rulemaking/committees/documents/media/LAFSLPARC-8202009.pdf

For an example of what lightning can do, look at the KATO Do228 accident (LN-HTA) https://www.aibn.no/Aviation/Reports/2007-23-eng
The elevator control rod end was blown out (due to a faulty bonding lead) and rod joints in the cockpit were overheated by a strike to the elevator.

[Nil by mouth]

Quoting from the CompositesWorld web-site, the spray on protection could be the panacea for lightning protection, easy to apply and easy to repair:-

NIAR’s Kostogorova-Bellar and Paul Jonas, director of NIAR’s environmental test labs, are conducting a U.S. Air Force-sponsored study on direct and indirect lightning and EMI shielding protection schemes for composite structures. One promising system is a conductive paint from Conductive Composites, in which the company disperses its nickel Nanostrand material. Formulated to handle lightning strikes in Zones 1A and 2A, the paint reportedly offers what Kostogorova-Bellar calls “superior” performance when compared to baseline LSP protection, such as aluminum and copper expanded foils and woven wire materials, including phosphor bronze. The paint, which reportedly can be resprayed in the event of damage, is expected to be a good alternative to the other methods.

[turbidus]

Maybe I just attract the wrong sorts! :}

Doesn't everyone have the problem with street lights going out when you walk past??

Wait..on a serious note...Boeing asked for the reduction in copper foil, before or after, they realised workers were grinding it off during assembly???

[Grebe]

Maybe I just attract the wrong sorts! :}

Doesn't everyone have the problem with street lights going out when you walk past??

Wait..on a serious note...Boeing asked for the reduction in copper foil, before or after, they realised workers were grinding it off during assembly???
Think you are conflating 7 late 7 wing foil issues versus 737 MAX engine cover issues - both relating to lightning . .

has to do with Arcs and Sparks .. :rolleyes:

[Dave Therhino]

Hi TD. I'm not positive, but I'm pretty sure that would be "once every fifteen years per aircraft," or about once every 50,000 flight hours, as opposed to once every 50,000,000 hours if it was once every fifteen years for a fleet of 1000 airplanes for strikes near 100kA and above. I could be wrong. I don't know that aspect of the industry data either, but I know someone who does. I'll ask him and report back.

My colleague confirmed the 200 kA peak current in the SAE model is based on the 95th percentile strike from data measured at multiple ground towers over several decades. Although the calculation is extremely crude, and probably off a bit, Boeing's ballpark once every 15 years for a maximum design level strike would be rate per airplane, not rate per fleet.

TD - Perhaps you were remembering estimates for the rate of maximum strike attachments to nacelles? Attachments to nacelles are only a few percent of the total attachments to the airplanes.

[golfyankeesierra]

So nothing to worry about. The frequency of a catastrophic strike which can blow up your plane when it strikes a tricky spot, is only one in fifteen years.

In the meantime, a regular(?) strike still happens yearly on average, taking the aircraft out of business from several hours to a day for a conventional aircraft (73,74). On the A330 I believe it usually is more like a day already, wonder what it will be on the B787.
I am not a mechanic but I understand most of the time is needed to find the entry and exit spots and assess whether damage was present (usually not). This has to be done in daylight or in a hangar. Now if you have to start repairs as well, it will be a lengthy AOG.
And BTW, I guess have had around 10 strikes myself in 25+ years, the one in every 3000 hours works for me..

[Australopithecus]

I think that I have had four or five strikes in 36,000 hours. I may in fact be a pussy after having been driven within 2 nm of an active tornado as a youth. Didn't much care for the bruises from the shoulder harness nor the yips, groans and screams heard over the noise of the T-56’s . My last strike was suffered in the hold at BETTY near Hong Kong a few years ago. About 7nm from the nearest wx rdr return. Right on the left windscreen wiper. Woke me from a sound slumber. That 330 took three days to repair and many beers to debrief. Big fan of aluminium, avoidance, and enhanced debriefing sessions.

[Luc Lion]

Without wishing to start Boeing versus Airbus debate, does the A350 have the foil in the wings?
The question is only because, if the wing construction is broadly similar and EASA / Airbus require it, that is strong evidence that the FAA should have insisted.
Yes it does, it(The A350) has copper sandwiches embedded in the CRP wing.
Yet, Airbus also finds that it is very difficult to prove that lightning related ignition sources in fuel tanks are extremely improbable (< 1 x 10^-9).
Back in 2014, they requested from the FAA that the proof of extreme improbability is moved from ignition sources to fuel-tank vapour ignition.
This switch allows to factor the use of inerting gas in the probability calculation.

https://www.federalregister.gov/documents/2014/09/08/2014-21245/special-conditions-airbus-model-a350-900-airplane-lightning-protection-of-fuel-tank-structure-to

As this came after the B787 certification (August 2011), it may be that Boeing wanted to benefit from this change in probability calculation rules.

[SLF3]

So is working nitrogen inserting MEL for the Bus? An earlier post suggested It isn’t for the 787.....

again, I’m not interested in a Boeing versus airbus debate, just looking for regulatory consistency around composite wings and lightning strikes.

[Dave Therhino]

Yet, Airbus also finds that it is very difficult to prove that lightning related ignition sources in fuel tanks are extremely improbable (< 1 x 10^-9).
Back in 2014, they requested from the FAA that the proof of extreme improbability is mov787 Lightning strike issues v FAA (https://www.pprune.org/rumours-news/627922-787-lightning-strike-issues-v-faa.html)ed from ignition sources to fuel-tank vapour ignition.
This switch allows to factor the use of inerting gas in the probability calculation.

https://www.federalregister.gov/documents/2014/09/08/2014-21245/special-conditions-airbus-model-a350-900-airplane-lightning-protection-of-fuel-tank-structure-to

As this came after the B787 certification (August 2011), it may be that Boeing wanted to benefit from this change in probability calculation rules.

The 787 special conditions contained the same allowance to use probability of flammability in the overall catastrophic explosion probability calculation. Both sets of special conditions were consistent with a 2009 policy memo released by the FAA.
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/12350ae62d393b7a862575c300709ca3/$FILE/ANM-112-08-002.pdf

That memo was later superseded by this 2014 memo.
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/3cfa83c3b327d06c86257d1700654329/$FILE/PS-ANM-25.981-02.pdf

Both memos have the same allowance for inclusion of flammability. Both were issued after public comment periods.

[Dave Therhino]

So is working nitrogen inserting MEL for the Bus? An earlier post suggested It isn’t for the 787.....

again, I’m not interested in a Boeing versus airbus debate, just looking for regulatory consistency around composite wings and lightning strikes.

The 787 inerting system is allowed to be inoperative under the MEL. The effect of this allowance was required by the special conditions to be included in the numerical probability analysis.

[Yaw String]

After reading about the exclusion from the original 2011 design,of the copper foil below the carbon composite surface and the insulating sealant that capped the heads of the fasteners,I am less and less inclined to accept the merit of the MEL relief for nitrogen system inop!
Where does cost cutting in the face of good practice end!
​​​​​​​

[A30_737_AEWC]

Short answer: The fibers in carbon composite are not continuous, but embedded in a non-conducting polymer matrix.

Short answer maybe - but highly misleading.

Carbon fibre reinforced composites utilised in primary airframe structures are generally of the prepreg tape or woven cloth type. Cylindrical-structures may also be filament wound. Characteristic of all these forms is that the reinforcing fibres are continuous. Fibres are usually bundled in tows and woven to form the dry cloth reinforcement.

Polymer matrices reinforced with discontinuous fibres are generally employed for secondary/tertiary structures where structural integrity is not the primary design requirement.

[Grebe]

Short answer maybe - but highly misleading.

Carbon fibre reinforced composites utilised in primary airframe structures are generally of the prepreg tape or woven cloth type. Cylindrical-structures may also be filament wound. Characteristic of all these forms is that the reinforcing fibres are continuous. Fibres are usually bundled in tows and woven to form the dry cloth reinforcement.

Polymer matrices reinforced with discontinuous fibres are generally employed for secondary/tertiary structures where structural integrity is not the primary design requirement.

You may be missing the point re lightning strike and composite. While prepreg tape is continuous fiber, when it comes to electrical conductivity - it doesn''t help UNLESS one figers out how to terminate each and every or at least most at both ends of the tape for electrical continuity to metal grounded structure. And tapes are typically laid in angles between each pass or layer eventually resulting in a near 90 degrees difference between x layers thus requiring termination to ground for each layer to be effective. This since a high energy strike can easily penetrate several ' layers ' of prepreg. Add to that the relatively low current capability of each ' layer' of prepreg tape makes the continuity issue of carbon long continuous carbon fibers pretty much a non issue re lightning strike. For a crude example - grind up or cut a bunch of cured prepreg fibers- fill a small plastic box with the cut fibers. Now put one probe in opposite walls of the plastic box and measure the continuity between the probes. or put a high voltage circuit output on the probes and do the same test instead of an ohmmeter.

[clark y]

On the B787s my company operate, they never seem to lose static wicks with lightning strikes but there can be many (sometimes very many) exit points on the fastener heads. The Airbusses I’ve been around seem to lose static wicks.
If one looks in the main wheel well of a B787 you’ll see a green wire about the size of a garden hose. Engineers have told me it is to help with the bonding.

[clark y]

This reminds me of this thread-Lightning strikes and FBW aircraft: Airbus

[A30_737_AEWC]

You may be missing the point re lightning strike and composite. ................

Nope, not missing the point. Solely responding to the OP's single sentence post/response (# 26) regarding discontinuous fibres embedded in a non-conductive matrix. Not a typical method for fabrication of primary structures, most of which must also display adequate conductivity to address lighting strikes, p-static dissipation and the general electrical bonding requirements of airframe structures.

Now, to address yours...........

Woven and knitted dry fibre preforms for structural components (which is where the research/fabrication developments in composite primary structures have been moving in recent years) lend themselves towards having suitable conductive meshes/conductive 'fingers' at attachment points, etc. incorporated into them, ahead of their impregnation with structural resins (see 'resin transfer moulding', 'resin infusion', etc.). I'm not aware that these approaches have been validated in widespread use, but I can see the potential benefits.

Can you give me some real-world airframe examples where every lamina in a laminate (via the conductive fibres) is effectively electrically bonded to adjacent structure ? Open question. I haven't seen many solid monolithic laminates (fighter aircraft wing skin, 50 plies) or honeycomb panels (fibreglass/carbon/boron skins, aramid cores) with the kind of treatment you suggest. Probably because it's that airframe structures must be producible and are not 'science experiments'. The conductivity is typically effected through the outermost plies/surfaces or with conductive surface coatings/diverter strips/etc. grounded to the adjacent mounting/support structures.

Taking your point on grounding all lamina of a laminate (monolithic or honeycomb with facings), look at how non-metallic radomes survive lightning strikes. Not very well, usually. Conductivity and RF transparency (active/passive systems) are competing performance requirements, with the later usually trumping the former.

[Grebe]

Can you give me some real-world airframe examples where every lamina in a laminate (via the conductive fibres) is effectively electrically bonded to adjacent structure ? Open question.

Guess I didn't make myself clear- my point was that UNLESS one could reasonably figure out HOW to ground both ends of a ' layer' of prepreg tape, the issue of continuity of a fiber layer was of no consequence re LIGHTNING STRIKE. I was not talking about structural issues.

I am not aware of any airframe that even tries to accomplish that re lightning protection. As to various methods eg imbedded mesh, foil, metal paths, conductive paint AFIK they all have their place. In some cases, re the protection of penetrations of composite structures by metal things like pumps, structure fittings, etc, copper plating on both sides and ' hole' of the penetration does work but is normally too expensive - complex to do for commercial production.