amicus
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FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 5:03 am

On March 30th, the FAA issued "proposed special condition" re "Composite Wing and Fuel Tank Structure- Fire Protection Requirements" (Docket Number NM366, Notice No. 25-07-03-SC). Proposed condition requires: "Boeing to demonstrate acceptable post-crash survivability in event wings are exposed to large fuel-fed ground fire. Boeing must demonstrate that the wing and fuel tank design can endure an external fuel-fed pool fire for at least 5 minutes. Considerations shall include fuel tank flammability, burn through resistance, wing structural strength retention properties and auto-ignition threats during a ground fire event for the required time duration."

Comments and observations, please.
 
FriendlySkies
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 5:15 am

Sounds fair...

And from testing of the CFRP material, the burn-through time is actually greater than that of aluminum. I'm sure Boeing isn't sweating over this.
 
Ferret
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 5:57 am

How do these requirements differ, if at all, from a conventional wing and tank requirement?
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Curmudgeon
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 5:59 am

That's interesting. I wonder if the test conditions call for full or nearly empty tanks? Does someone have the aluminum wing requirements (if any) handy? (Fuselage skins have burned through in 12 seconds, as I recall from one accident report).

A friend was in a 737 fuel truck fire incident like this...a burning pool of fuel under the aircraft. It occurred before passenger boarding, and he reports that the entire aircraft was ablaze within 3 minutes-a total loss even with a quickish response from the airport fire service.
Jets are for kids
 
sphealey
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 6:05 am

> Comments and observations, please.

I guess the proof test article won't be going to a museum  Wink

sPh
 
cygnuschicago
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 6:05 am

That's interesting - won't these same conditions already be in place for Airbus aircraft with composites in the wing, especially the A400M, or is it exempt as it is a military plane?

Quoting Amicus (Thread starter):
Comments and observations, please.

You sound like a schoolteacher
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777236ER
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 6:09 am

A good thing from the point of view of passenger safety. Legislation is surprisingly lax regarding pooled-fuel fires - see the Manchester airport fire to see just how rapidly devastating they can be.
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KELPkid
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 6:19 am

Quoting FriendlySkies (Reply 1):
And from testing of the CFRP material, the burn-through time is actually greater than that of aluminum. I'm sure Boeing isn't sweating over this.

Wonder if ARFF services around the world will have to update the firefighting foam that they use? Isn't it designed mostly to keep metal from burning, and not primary carbon structure?
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
 
LMP737
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 6:21 am

Quoting CygnusChicago (Reply 5):
That's interesting - won't these same conditions already be in place for Airbus aircraft with composites in the wing, especially the A400M, or is it exempt as it is a military plane?

I don't what the laws are in Europe regarding military aircrat but in the US any aircraft that's to fly for the US military has to show a certain level of survivablity.
Never take financial advice from co-workers.
 
MCIGuy
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 6:36 am

This is kind of old news. Of course there will be new hoops for the first plastic airliner to jump through, there should be given the radical departure from traditional design. Last I heard, Boeing is helping the FAA "write the book" on the 787 and future composite planes.
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amicus
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 6:57 am

Under "novel and unusual design features proposed SC states:
" Conventional aircraft with aluminum skin and structure provide a well understood level of safety during post-crash scenarios with respect to fuel tanks.......Composites may or may not have capabilities equivalent to aluminum and current regulations do not provide objective performance requirements for wing and fuel tank structure with respect to post-crash safety."
Also per SC:
" The extensive use of composite materials in the design of the 787 wing and fuel tank structure is considered a major change from conventional and traditional methods of construction This is the first large transport category aircraft to be certificated with this level of composite material for these purposes. The applicable airworthiness regulations to not contain specific standards for post -crash fire safety performance of wing and fuel tank skin or structure. "

Re earlier fuel load question:
SC states:
"This shall be demonstrated for minimum fuel loads (not less than reserve fuel levels) and
maximum fuel loads (maximum range fuel quantities) and other identified critical fuel loads".

Quoting CygnusChicago (Reply 5):
That's interesting - won't these same conditions already be in place for Airbus aircraft with composites in the wing, especially the A400M, or is it exempt as it is a military plane?

Quoting Amicus (Thread starter):
Comments and observations, please.

You sound like a schoolteacher

No, just a aerospace composites structural engineer with over 40 years of composites experience.

Quoting FriendlySkies (Reply 1):
Sounds fair...

And from testing of the CFRP material, the burn-through time is actually greater than that of aluminum. I'm sure Boeing isn't sweating over this.

Sensible engineers sweat everything until proven by test and Boeing has lots of sensible and superb engineers and I am sure will be sweating it until all results of test are in.
 
amicus
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 7:03 am

Quoting MCIGuy (Reply 9):
This is kind of old news. Of course there will be new hoops for the first plastic airliner to jump through, there should be given the radical departure from traditional design. Last I heard, Boeing is helping the FAA "write the book" on the 787 and future composite planes.

I fail to see as old news if FAA just published proposed SC on March 30th 2007
 
EI321
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 7:13 am

Quoting Amicus (Thread starter):
Comments and observations, please.

Interestesting. Was Boeing expecting this?
 
MCIGuy
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 7:33 am

Quoting Amicus (Reply 11):
I fail to see as old news if FAA just published proposed SC on March 30th 2007

I was just saying that there was a recent thread about this already. Nothing personal man, no insult intended. Smile
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Curmudgeon
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 7:39 am

The more that I reflect on this SC, as noted in Amicus's brief, the more I wonder if this isn't shooting from the hip on the part of the FAA.

1. Their stated aim is to ensure an equivalent level of safety to aluminum wings.
2. They are releasing this now, on the eve of the test program? Are they just getting around to thinking about the ramifications of composites?
3. Have they tested a representative sample of conventional wing structures? If not, why not? How have they
determined that five minutes fire resistance is equivalent to a metal wing? What if someone showed a metal wing burning through in less than five minutes? Does the test requirement call out temperatures, or elevation of the structure above the fuel pool?
4. On the face of it, an aerated fuel pool fire below the wing structure would be pretty hard to resist, I'd think. The temperatures reached could be ferocious, and 300 seconds is a long time.
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Stitch
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 7:46 am

Well some folks were recently of the opinion that the FAA was going to "cook the books" to give the 787 a cleaner (and, allegedly, riskier to passengers) path to certification. So if the FAA is indeed requiring Boeing to at least meet current standards on Al aircraft then that will hopefully allay some of the possible fears the traveling public may have.

[Edited 2007-04-10 00:50:15]
 
pygmalion
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 7:48 am

Boeing has been working special condition definitions with the FAA since the start of the program. It's all about defining the cert basis for the aircraft. Since no regulations exist for this... Boeing, the FAA and EASA work together to define new ones. Special conditions are how new, novel parts/constructions are handled.

When the regulations don't define how to certify a new design, the manufacturer and the regulatory agency work together to define how they will certify the aircraft is airworthy. This should be no surprise to anyone and is not a surprise to the FAA and Boeing.
 
Ruscoe
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 8:14 am

Quoting Amicus (Reply 10):
No, just a aerospace composites structural engineer with over 40 years of composites experience

Would you mind giving us your thoughts on how Composites might behave in this situation?

Thanks
Ruscoe
 
ikramerica
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 8:24 am

I guess 5 minutes is the time they've decided that survivors would need to assess the situation, open the doors, evacuate and get far enough away from the plane so they wouldn't be killed from the explosion.

One assumes there can only be a "pooling" fuel fire if the plane has come to rest, right?
Of all the things to worry about... the Wookie has no pants.
 
EI321
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 9:05 am

Quoting Stitch (Reply 15):
Well some folks were recently of the opinion that the FAA was going to "cook the books" to give the 787 a cleaner (and, allegedly, riskier to passengers) path to certification.

I think that assertion (by some) is BS. Neither Boeing nor the FAA can afford to play that kind of game. Theres just too much riding on the 787 to risk cutting corners like that.
 
ChiGB1973
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 9:06 am

If you can't get out, a 5 minute window might mean the difference between fire/rescue arriving on scene in time to keep you from essentially baking in an oven. I am just assuming that the aircraft isn't escapable, fire/rescue could arrive within 5 minutes and there is a pool of fuel burning. Many assumptions; the LEX accident might have added some concern, if, in fact, this was a factor.

M
 
ikramerica
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 9:19 am

Quoting ChiGB1973 (Reply 20):
I am just assuming that the aircraft isn't escapable, fire/rescue could arrive within 5 minutes and there is a pool of fuel burning.

That's a good point. On a runway overrun, 5 minutes should be enough time for crews to arrive and start putting it out, but I can't see them getting it completely under control in that time.

Then again, I'm not a fireman, so maybe they can?!
Of all the things to worry about... the Wookie has no pants.
 
domokun
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 9:43 am

Quoting ChiGB1973 (Reply 20):
If you can't get out, a 5 minute window might mean the difference between fire/rescue arriving on scene in time to keep you from essentially baking in an oven. I am just assuming that the aircraft isn't escapable, fire/rescue could arrive within 5 minutes and there is a pool of fuel burning.

If you can't get out, you have a separate major problem. What if nobody could have gotten of the AF A340 which overran? Fire survivability is one thing, getting out is another  Smile
 
ChiGB1973
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 9:50 am

Quoting Domokun (Reply 22):
If you can't get out, you have a separate major problem.

I don't know that I would say separate, just additional.

M
 
HughesAirwest
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 11:18 am

I remember back in August of 06 that either NGC or Discovery channel had a special on the A380 and the cameras had to be turned off due to the "special" bonding process of there wings. Aren't the A380's wings made up of composites? If so the why did Airbus not have to demonstrate this.
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amicus
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 11:41 am

Seems time to surface again to answer some of the excellent points raised in this thread.

Quoting MCIGuy (Reply 13):
Quoting Amicus (Reply 11):
I fail to see as old news if FAA just published proposed SC on March 30th 2007

I was just saying that there was a recent thread about this already. Nothing personal man, no insult intended.

No offence here, but if you check earlier thread, I was offering some rather detailed thoughts re FST (Fire, Smoke and Toxicity) and crash-worthiness of composites. It applies to both 787 and A-350XWB and possibly to A-380, given the center wing box in cf/epoxy . Unfortunately that thread had a somewhat obscure title re crash-worthiness and FST being entitled 787-10 first picture. Please review what I said in that thread also if you have an interest in this subject. I could quote all my earlier stuff, but if you check that thread you will find my basic position and again, no offence here.

Quoting Curmudgeon (Reply 14):
The more that I reflect on this SC, as noted in Amicus's brief, the more I wonder if this isn't shooting from the hip on the part of the FAA.

1. Their stated aim is to ensure an equivalent level of safety to aluminum wings.
2. They are releasing this now, on the eve of the test program? Are they just getting around to thinking about the ramifications of composites?
3. Have they tested a representative sample of conventional wing structures? If not, why not? How have they
determined that five minutes fire resistance is equivalent to a metal wing? What if someone showed a metal wing burning through in less than five minutes? Does the test requirement call out temperatures, or elevation of the structure above the fuel pool?
4. On the face of it, an aerated fuel pool fire below the wing structure would be pretty hard to resist, I'd think. The temperatures reached could be ferocious, and 300 seconds is a long time.

I am full of praise for the FAA's actions and take the view that it is better late than never. The FAA is taking a strong position which is, in essence, prove it re safety to the manufacturers. This is the duty of the manufacturers, I believe, and passenger and crew safety together with firefighters and others is both proper and necessary.This is the proper position to adopt, I believe, on the part of certificating authorities. The basic problem, as I discussed in the earlier thread, is that strong regulations exist with respect to interiors composites and banning of epoxies and their replacement by phenolics many years back, but there are currently no regulations for exteriors composite parts at all. Hence the only path for certifying agencies is to impose "Special Conditions" if suitable data base does not exist, which in my view, doesn't.
I had lurked for many months on this forum and enjoyed the vigorous give and take and knowledge of members displayed by many members, however, I was disappointed that this issue had not been raised previously and so I joined and posted my thoughts an an earlier and somewhat obscurely named thread earlier thread.
I do think that there exists a major safety issue crash-worthiness and FST issue which needs to be addressed and am grateful to FAA for moving ahead to address it. The 5 minute proposed requirement by the FAA is based upon many years of experience with aluminum crashes and fires, The FAA, as I understand it, is saying to both Boeing and Airbus, must ensure that this same standard is met for composites. That is rational and reasonable in my view. One can criticise the authorities, but they have now acted and prior to , first flight, certification and EIS. As an aside, I do have an issue with A-380 center wing box in cf/epoxy regarding crash-worthiness, but that A/C is already certified, but there is still time to ensure that 787 and A-350 meets safety requirements.

Quoting Ruscoe (Reply 17):
Quoting Amicus (Reply 10):
No, just a aerospace composites structural engineer with over 40 years of composites experience

Would you mind giving us your thoughts on how Composites might behave in this situation?

Thanks
Ruscoe

In my opinion, given the high flammability and toxicity of cf/epoxies, I would rate chances of success for five minute test success on low side, but have been wrong before, which is why we engineers believe in having rubber on the end of our pencils.
 
amicus
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 12:19 pm

Quoting EI321 (Reply 12):
Quoting Amicus (Thread starter):
Comments and observations, please.

Interestesting. Was Boeing expecting this?

Certainly, and there was a recent clue in the 787 quarterly web-cast where it was mentioned that:
"There is a lot of debate going on internally whether to take static test article to failure or only to 150%".
This was discussed in another thread, but there might be a use for that test frame re FAA SC possibly explaining that debate and its cause if one wants to speculate.
 
Ruscoe
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 2:43 pm

Quoting Amicus (Reply 25):
I would rate chances of success for five minute test success on low side,

Thankyou for that.

So if it fails to meet the 5 minute rule, is there a fix which could be incorporated within the certification testing time frame, or would we be looking at a program delay?

Ruscoe
 
Curmudgeon
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 4:06 pm

Quoting Amicus (Reply 25):
The FAA is taking a strong position which is, in essence, prove it re safety to the manufacturers. This is the duty of the manufacturers, I believe, and passenger and crew safety together with firefighters and others is both proper and necessary.

 checkmark 

Quoting Amicus (Reply 25):
As an aside, I do have an issue with A-380 center wing box in cf/epoxy regarding crash-worthiness, but that A/C is already certified



Quoting Curmudgeon (Reply 25):
2. They are releasing this now, on the eve of the test program? Are they just getting around to thinking about the ramifications of composites?

This goes to my sarcastic comment about only just realising this now. They knew that composites were coming for quite some time now, and they missed the first aircraft by a few months. If you think that epoxy matrix composites present a flammability issue, and there are aircraft with this material in this (now newly flagged) critical area, why were the new regs or SC's not in place in time to assure the desired level of safety in all aircraft?

Quoting Amicus (Reply 25):
I do think that there exists a major safety issue crash-worthiness and FST issue which needs to be addressed and am grateful to FAA for moving ahead to address it.

Again, so am I, but what does this have to do with crash worthiness? If a wing ruptures and spills it's fuel, I don't think that tank explosion is the greatest subsequent risk-its fuselage burn through and pool spread into the escape paths.

Quoting Amicus (Reply 25):
The 5 minute proposed requirement by the FAA is based upon many years of experience with aluminum crashes and fires,

I'm still wondering if there a body of evidence that indicates that 5 minutes is somehow the magic number to achieve equivalency, or is it some number that they think is 'reasonable', like the RTO fire requirements?

Quoting Amicus (Reply 25):
One can criticise the authorities, but they have now acted and prior to , first flight, certification and EIS.

No, they haven't. See above re A380, both my comments and yours.

Quoting Amicus (Reply 25):
In my opinion, given the high flammability and toxicity of cf/epoxies, I would rate chances of success for five minute test success on low side,

So then tell me again how Boeing and the FAA have jointly written the book on composites so that a new requirement is issued so late in the product development cycle. I am still glad that its being checked, but if there's any doubt about the results I can't believe that anyone is too happy about it.
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Ruscoe
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 8:59 pm

To answer my own question,I have asked a non aerospace engineer who has general knowledge, and he said that heat damage to CFRP laminates, spreads rapidly laterally but does not penetrate quickly, because the layers delaminate and act as an insulating barrier to further fire penetration.

Maybe it will pass the 5 minute rule.

Ruscoe
 
mustang304
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RE: FAA Issues Proposed Special Condition Re 787

Tue Apr 10, 2007 11:58 pm

Quoting LMP737 (Reply 8):

The military transport plans are sometimes equipped with a system called OBIGGS (On Board Inert Gas Generating System), a system that produces Nitrogen to blanket the tanks and spaces around them. It is designed to prevent aircraft loss from small arms fire penetrating the fuel tanks. It would prevent/minimize this issue as well.

As for the composite structure, I don't think they are in new territory here- remember Boeing was involved in the stealth bomber project. I'd also suspect that their DERs have been looking at this issue since the plane was first given the green light. I'd predict that they have designed for the requirement, they just need to show compliance. The testing is expensive, as an identical mock-up of the system has to be built, and then the actual test needs to be performed. Airframe and aircraft component manufactures try their best to use analysis and similar tests to show compliance to the FARs, but sometimes, as in this case, they just need to do the test.


Mustang304
 
NYC777
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 12:47 am

From what I understand Boeing IS going to be using a nitrogen generator (similar to OBIGGS) for the fuel tanks on the 787 to fill up the empty space. It is currently being tested on a pair of 747's and a few 737's as we speak.
That which does not kill me makes me stronger.
 
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USAF336TFS
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 3:49 am

Quoting Ruscoe (Reply 27):
So if it fails to meet the 5 minute rule, is there a fix which could be incorporated within the certification testing time frame, or would we be looking at a program delay?

I'll go out on a limb here and say that there are those that are praying for anything would provide a pretext for a program delay.

The bad news for them is, that this issue is probably already addressed.

[Edited 2007-04-10 20:50:31]
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Stitch
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 4:57 am

Does not the fuel tank inerting standard apply only to the center fuel tank, which the A388 does not have? I am pretty sure that Airbus has said it will be present on the A388F (and A388R/A389 if launched) as they will have a center fuel tank.

I believe Boeing is just going "above and beyond" by putting it in the wing tanks as well as the center tank, even though wing tanks are not required to have it.
 
Rheinbote
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 5:34 am

A few things to consider:
- the A380's CFRP center wing box is almost completely buried within the fuselage, the wing boxes sticking out left and right are metal.
- composite wings are likely to require an inerting system for lightning strike protection, anyway
- CFRP fuselage skins proved to be superior to aluminum skins in burn-thru tests
 
amicus
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 6:34 am

Quoting ChiGB1973 (Reply 23):
Quoting Amicus (Reply 25):
The FAA is taking a strong position which is, in essence, prove it re safety to the manufacturers. This is the duty of the manufacturers, I believe, and passenger and crew safety together with firefighters and others is both proper and necessary.



Quoting Amicus (Reply 25):
As an aside, I do have an issue with A-380 center wing box in cf/epoxy regarding crash-worthiness, but that A/C is already certified



Quoting Curmudgeon (Reply 25):
2. They are releasing this now, on the eve of the test program? Are they just getting around to thinking about the ramifications of composites?

This goes to my sarcastic comment about only just realising this now. They knew that composites were coming for quite some time now, and they missed the first aircraft by a few months. If you think that epoxy matrix composites present a flammability issue, and there are aircraft with this material in this (now newly flagged) critical area, why were the new regs or SC's not in place in time to assure the desired level of safety in all aircraft?

Quoting Amicus (Reply 25):
I do think that there exists a major safety issue crash-worthiness and FST issue which needs to be addressed and am grateful to FAA for moving ahead to address it.

Again, so am I, but what does this have to do with crash worthiness? If a wing ruptures and spills it's fuel, I don't think that tank explosion is the greatest subsequent risk-its fuselage burn through and pool spread into the escape paths.

Quoting Amicus (Reply 25):
The 5 minute proposed requirement by the FAA is based upon many years of experience with aluminum crashes and fires,

I'm still wondering if there a body of evidence that indicates that 5 minutes is somehow the magic number to achieve equivalency, or is it some number that they think is 'reasonable', like the RTO fire requirements?

Quoting Amicus (Reply 25):
One can criticise the authorities, but they have now acted and prior to , first flight, certification and EIS.

No, they haven't. See above re A380, both my comments and yours.

Quoting Amicus (Reply 25):
In my opinion, given the high flammability and toxicity of cf/epoxies, I would rate chances of success for five minute test success on low side,

So then tell me again how Boeing and the FAA have jointly written the book on composites so that a new requirement is issued so late in the product development cycle. I am still glad that its being checked, but if there's any doubt about the results I can't believe that anyone is too happy about it.

Regarding your responses and thoughts, I could answer point by point, but think more useful, first, to discuss background and known issues. First, obviously Boeing DER's and FAA work closely together at all times, sometimes there are areas of agreement and sometimes areas of disagreement, these situations are normal, but the tasks of both are to ensure passenger, crew and firefighters and both would strive to do this at all times. Now, with respect to epoxy matrices and composites, there has been a known FST issue (and let us also ponder on the toxicity and smoke issues as well as fire) since late 1960's. This led to a large FAA and NASA led effort to better protect passengers and crew via substitution of phenolic matrices for previous epoxy matrices regarding A/C interiors. Efforts have been made to enhance fire resistance of epoxies and at one point , I would note,Boeing was proposing aluminum interiors. The end result was banning of epoxies for interiors and their replacement via phenolic matrices. Numerous passengers and crew had unfortunately been killed in the interim by FST of epoxy matrices composites in what many would describe as survivable crashes.
At this point, certification authorities have good experience, excellent regulations and wide in-service database concerning the utility of phenolics interiors over epoxies in enhancing safety, there is no more debate over that issue and both aircraft and offshore oil rig fires have repeatedly proven the efficacy of phenolics in FST area. That is not to say that phenolics are perfect, merely that they are markedly superior to epoxies. Chemists and engineers have also striven to make epoxies very low risk regarding FST, but I would say, at this point, not with a great deal of success in my opinion, and phenolics remain the standard for interiors at this time. Note also, again, there is a major toxicity and smoke issue for epoxies, which must also be considered and designed against, this issue should not be skirted around or forgotten either, toxicity and smoke can kill as fast ot faster than fire in crash situations.
Back in middle to late 70's epoxy based composites were considered, designed and certified for usage in commercial A/C, examples being the vertical and horizontal empennages of A-310, A-300 and the A-320 series which have been in production since that time. Also, various secondary structures from both Boeing and Airbus were designed and certified. No regulations, to my knowledge, existed then or exists now for FST issues on external composites, but I would say that when fuel tanks entered the picture as in the horizontals of A-340 et al, the certificating authorities began to scrutinise more closely and some regulatory points were raised and discussed as is discuussed by the FAA in the current proposed Special Condition. The A-340 crash at Toronto brought home the need for such new scrutiny.
Turning to what generally happens internally concerning composites and other materials, it is, in my experience, that the manufacturer seeks to define, test and prove "Equivalence to Aluminum" as the standard and the certifying agencies then assess from analyses, tests and data submitted by the manufacturer, the degree of risk, together with many other factors from which either the certifying agency accepts the equivalence to aluminum arguement or, if data base is unsatisfactory or deemed too risky, will impose Special Conditions imposing other tests and requirements. These areas for both certifying authorities and for aircraft manufacturers are seldom black and white, but rather we all work in shades of gray.
Sorry about the long preamble, but am trying to put things into context. Now we come to the, in essence, all composite epoxy 787 and A-350-XWB A/C, here there is a major expansion of previously limited usage of epoxy matricies and that is a risk Boeing and Airbus took knowing full well the risks that they could not satisfy FAA and JAA. It is not the job of certifying agencies to ban innovative design, but to ensure safety and compliance with regulations and that, if existing regulations are deemed not adequate, to impose Special Conditions regarding "novel and unusual design features and issues".
Boeing, over the past years , I would be certain, has worked in close concert with FAA et al trying to prove "aluminum equivalence" for the 787. This, for example, is why Boeing performed burn through tests as well as many others in the area of flammability an honest attempt to prove to the certifying agencies the cf/epoxy 787 structure was met previous crash-worthiness stands of aluminum. Again, this would have been a cooperative effort and by no means implies that suddenly in March 2007, the agency out of the blue decides a new test. I don't think that there is a blame game involved nor do I think it productive to engage in one in this forum. The risk always was and is on Boeing and Airbus in using new materials in novel and new manners and designs where regulations were not in place previously. The certifying agency, in this case, appears to believe that Boeing has not yet proven their case sufficiently or that the risks are too high without a crash-worthiness fire test to prove or disprove aluminum equivalence.
Boeing engineers knew the risks full well going in and, if they are right, they will pass the test to the satisfaction of the FAA. If they fail the test that is another issue, but I think it grossly unfair is characterize the agency as very late, there is a shared cooperative effort here with the burden of proof being upon Boeing to now demonstrate aluminum equivalence. I will never fault an agency for fulfilling it public safety role and I would hope others on this forum would agree. In short, there is a significant issue, FAA is not presently satisfied regarding aluminum equivalence and so Boeing must demonstrate by test that their structure is "aluminum equivalent. You could fault an agency for not doing its job, but never for doing its clear duty regarding passenger and crew safety. There is no blame in my mind, only both manufacturer and certifying agency are doing their jobs in proper manner.
Sorry, my post so long, but hope of some interest.
 
Curmudgeon
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 8:22 am

Speaking as the chief protester in this thread, thanks very much for your thoughtful and informative reply. Your background information is clear and helpful, as are your arguments.

I want to clarify my position on the FAA thus: I think that in the main (and now observing from afar) they do a great job, and are often the sole source in accessible information on aspects of safe operation. They are not, however, above criticism in many areas, not least the timely implementation of recommendations of the NTSB, for example*

In this case my bewilderment stems from the fact that there are two new mostly composite airliners entering service soon, and one or two more on or near the drawing board. This SC completely missed the A380 which also, as you pointed out, an epoxy matrix fuel tank. (and a larger pax load to egress). That the A380 just gained a type certificate without being tested means to me that the regulator just missed in issuing the SC in a timely fashion.
I am not Airbus bashing by any means, just wondering at the timing.

*not that every NTSB recommendation can be implemented, or has merit.
Jets are for kids
 
pygmalion
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 8:25 am

Another piece to this story is that putting out a "proposed special condition" for comments is where the non-boeing community gets to weigh in on the proposal back to the FAA. This would include Airbus cert focals and other country's regulatory agencies. Neither the FAA nor Boeing is surprised by what is in the special condition. Boeing and the FAA, I am sure, have been in consultation on building the certification basis for the aircraft and nothing here is a surprise. .

Another point. These cert discussions start early in the program. Above some have made comments about the A380 and what was included or not in their cert basis for that aircraft. ALL manufacturers work with the regulatory agencies so that there are no surprises on how the aircraft with will be evaluated for certification. The A380 special conditions were generated in 1998 IIRC. Much of the current discussion on nitrogen generation happened after that and IMHO is the reason NGS was not included in early model A380's, not because Airbus talked them out of it.
 
pygmalion
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 8:34 am

And to directly answer Curmudgeon's point... My best guess for the center wing tank on the A380 for fuel tank fire is that it is either shielded from fire by the under wing composite fairing or if the gear is up and the fairing crushed, by the ground. Flame impingement on the center tank is limited and I think that you could show that it meets a 5 minute burn through limit by small scale test. Having a wing suspended and exposed above a pooled fuel fire is a whole 'nother ballgame.
 
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Stitch
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 9:14 am

Quoting Pygmalion (Reply 38):
My best guess for the center wing tank on the A380 for fuel tank fire is that it is either shielded from fire by the under wing composite fairing or if the gear is up and the fairing crushed, by the ground.

The A380-800 does not have a center wing tank, so it doesn't need anything special.  Wink

The A380-800F does, but again, I believe Airbus has said they will install an inerting system in it to be in compliance with regulations calling for such systems, even though the design may not be required to by "grandfathering" clauses (and I don't know if such clauses apply).
 
Curmudgeon
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 9:30 am

Thanks, Pygmalion. I am even more bemused now, after reading your post that the A380 SC's were in place in 1998, before the program launch-compared to a 2007 SC so (seemingly) late for the 787. Since a test implies that the results can't be assumed, then it strikes me still as oddly timed. What do I know?

As far as the centre fuel tank on the A380, the same could be said of the rest of the tanks...collapsed gear will lower them all to ground height (except dihedral angle effects). I will opine that a burning centre tank will cause more immediate concerns than the relative toxicity of the smoke plume.

WRT to the safety of certain compounds in cabin fittings, the toxic effects are certainly a chief concern, and efforts to eliminate them are laudable, to say the least. The toxic effects of smoke in the wind field seem to me to be of a lesser direct threat, but I'm open to being convinced (or ignored) otherwise. If toxicity is going to be such an issue, then heat and other products of combustion are going to play a major role too.

Has anyone yet considered the effects of delaminated and freed carbon fibres in the egress path environment? I understand that these filaments may also pose a health risk if inhaled or otherwise ingested.

Cur...
Jets are for kids
 
pygmalion
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 10:29 am

Curmudgeon,

Just to be sure I didn't mislead.... Airbus asked for type cert basis definition for the A380-800 in 1998. The negotiations start then. Most items are fairly obvious in that they have been done before and the FAA and Airbus would have a clear road map to cert for most of the aircraft. Its in the places where the FARs dont apply that things get protracted. The cert basis agreements are good for 5 years. ( the A380 had to ask for a 2 year extension in 2005) The special conditions get finalized fairly close to final assembly somewhere around drawing 50% release on the aircraft. I believe that all the SC's for the A380 were refinalized in 2005. That being said... its very early in the process when the regulators and the manufacturers start determining what is needed to both make the aircraft safe, how to structure the regulation and how to test it to prove it. Airbus and Boeing have much more data and people than the FAA or EASA. I would call the FAA the Auditor. They come in and ask very pointed questions, Airbus and Boeing provide the answers and have to justify every bit of those answers to the FAA's satisfaction. When you go into places where no man has gone before... you write it down and it becomes a special condition with an agreement on how to demonstrate compliance.

No aircraft manufacturer wants to be surprised by a late cert requirement just prior to type cert when it is most expensive to fix. Early and frequent coordination is the solution.

Demonstration by test is the standard rule for all cert requirements. The trick is that most things have been tested before so there is a body of data that you can use to show that the design is good by analysis. I am not surprised that the FAA is asking Boeing to prove the SC by test. For example, I do know that, as a result of the interior cert requirements for FST, ALL new material layup combinations in the cabin are burn tested to ensure they pass.

My humble opinion is that Boeing has plans to show by test that the 787 meets the SC... I doubt very much if that means a full aircraft test in a burning pool of JetA. Flame heats and propagation are well known. I am sure Boeing will toast a large fueled wing section and test barrel like a hot dog over a BBQ and I am sure they already have that in the test plan.

you can look at SCs on the FAA regulatory website... lots of readin to wile away the hours for the design geeks out there.

See FAA Special Conditions

[Edited 2007-04-11 03:34:24]
 
pygmalion
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 10:33 am

also... engines hold the outer wing off the ground in most cases so the lower wing surface has more exposed burn area. Any part actually in the fuel won't burn as the fuel actually cools the part. The fuel only burns at the surface.

[Edited 2007-04-11 03:37:00]
 
amicus
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 10:42 am

Quoting Curmudgeon (Reply 40):
Has anyone yet considered the effects of delaminated and freed carbon fibres in the egress path environment? I understand that these filaments may also pose a health risk if inhaled or otherwise ingested.

Cur...

Cur,
All thanks for yours and your comments and insights, they are appreciated, and on this specific issue there was a bunch of research done during the '80's by DOD and NASA and as I remember the conclusions were that there are no significant health hazards resulting from free carbon, certainly nothing in comparison with FST from epoxies burning. So I think not a key issue. I think the main issue is getting passengers and crew out in case of fuel fire safely within the allotted time.

Quoting Stitch (Reply 39):
The A380-800F does, but again, I believe Airbus has said they will install an inerting system in it to be in compliance with regulations calling for such systems, even though the design may not be required to by "grandfathering" clauses (and I don't know if such clauses apply).



Quoting Pygmalion (Reply 38):
And to directly answer Curmudgeon's point... My best guess for the center wing tank on the A380 for fuel tank fire is that it is either shielded from fire by the under wing composite fairing or if the gear is up and the fairing crushed, by the ground. Flame impingement on the center tank is limited and I think that you could show that it meets a 5 minute burn through limit by small scale test. Having a wing suspended and exposed above a pooled fuel fire is a whole 'nother ballgame.



Quoting Stitch (Reply 39):
The A380-800 does not have a center wing tank, so it doesn't need anything special.



Quoting Curmudgeon (Reply 40):
Thanks, Pygmalion. I am even more bemused now, after reading your post that the A380 SC's were in place in 1998, before the program launch-compared to a 2007 SC so (seemingly) late for the 787. Since a test implies that the results can't be assumed, then it strikes me still as oddly timed. What do I know?

As far as the centre fuel tank on the A380, the same could be said of the rest of the tanks...collapsed gear will lower them all to ground height (except dihedral angle effects). I will opine that a burning centre tank will cause more immediate concerns than the relative toxicity of the smoke plume.

To Pygmalion, Cur and Stitch,
Thank you for your comments, but would add that tank inerting is not the total answer as that is an internal system, but fire hazard from friction during a wheels up landing is still an external ignition issue as it doesn't need to get too hot to ignite the epoxy matrix from ground friction, it is flammable stuff. So I still have concerns re A-380, but clearly is much greater issue re 787 and A-350. Anyhow the 380 is already certified, so we will have to wait and see regarding any in-service issues, let's hope not, but I still harbour doubts. I agree with Cur on this point and to Cur also; I think that the seeming lateness of the proposed SC may have lots to do with Boeing DERs continuing over past couple of years to submit test and analytical data to FAA trying to convince them of aluminum equivalence, but ultimately the FAA decided, rightly in my tendentious opinion, that a crash fuel burn test is required due to lack of large passenger commercial data base and lack of demonstrated aluminum equivalence. The risks are high and I believe that the proposed test will be of great value to both Boeing and Airbus engineers for future designs whatever the outcome as well as for commercial aviation worldwide.

Quoting Curmudgeon (Reply 36):
want to clarify my position on the FAA thus: I think that in the main (and now observing from afar) they do a great job, and are often the sole source in accessible information on aspects of safe operation. They are not, however, above criticism in many areas, not least the timely implementation of recommendations of the NTSB, for example

Cur,
I feel none of us are above criticism, agreed, I have certain issues with certificating agencies and I would bet that they do with me, but, as mentioned earlier, there are lots of gray areas in engineering and sometimes tests are the only rational and prudent course to pursue. Overall, I rank the FAA very highly as you do, particularly in this case.
 
XT6Wagon
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 11:07 am

Quoting Curmudgeon (Reply 3):
Fuselage skins have burned through in 12 seconds

Aluminum makes a great fuel. You at least used to be able to see when someone was about to lose their motor in NASCAR as it would suddenly be making alot more power than everyone else in the field. This is because the motor started to use the top of the piston for fuel. Aluminum burns with alot more energy than the gasoline so.... "free HP" till you lose the piston.

So aluminum is great but if you can get it to light off, it has ALOT more energy than any pool of gas. I think this is where the composites will be far safer than aluminum. Hard to light off, and they don't really want to burn even if you do get it set on fire.

Oh and for this test? composites should have a moderately easy time of it. LOTS of thermal mass in the skin, and good insulating properties. I think the only design challenges is to make sure the edges of the wing and any other transition are designed right as thats where the problems will be with burn through.
 
WingedMigrator
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 11:48 am

Quoting Stitch (Reply 39):
The A380-800 does not have a center wing tank, so it doesn't need anything special.

 checkmark 

Quoting Stitch (Reply 39):
The A380-800F does

Only as an option. I don't think that any of the former customers selected this.
 
flyabunch
Posts: 444
Joined: Fri Nov 05, 2004 1:42 am

RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 12:58 pm

Thanks for a great thread. I am not qualified to contribute to the substance of the discussion but that does not mean that I do not appreciate the topic. It has been educational and informative. We need more like this one.

Mike
 
Curmudgeon
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 2:45 pm

Quoting XT6Wagon (Reply 44):
This is because the motor started to use the top of the piston for fuel. Aluminum burns with alot more energy than the gasoline so.... "free HP" till you lose the piston.

This happened to me one night when the air cooling passage blocked on a cylinder in my 356. That was one comprehensively messed up motor afterward. Too bad I didn't have sponsors to bankroll the experiments of my youth Wink
Jets are for kids
 
MCIGuy
Posts: 1445
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RE: FAA Issues Proposed Special Condition Re 787

Wed Apr 11, 2007 3:26 pm

Quoting XT6Wagon (Reply 44):
Aluminum makes a great fuel.

Aluminum accounts for much of the product that's inside firecrackers.  Wink
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