A321XLR’s rear fuel tank demands special fire-protection conditions

Weatherwatcher1 · Mon Mar 01, 2021 7:06 pm

Tristarsteve wrote:
madpropsyo wrote:
I mean it's not just going to be cold feet, right? Those rows in the cabin over and near the RCT will be very cold in general if there's an icebox on the floor. So either the passengers in those rows will be very cold or the rest of the cabin will have to be overly hot to compensate. That is a pretty significant lose/lose comfort issue to work out and it's no wonder the airlines with orders are unhappy.

FluidFlow wrote:
So the design of the tank is actually safe but it is not comfortable, except for one risk that is an external fire:

Lol, yeah it's totally safe... except for the fire.

Why should there be an icebox on the floor.?
The fuel in that tank is inside the pressure hull. It is loaded at around 5 degC or more, and is then warmed up by the cabin air flowing around it. Depends how they vent it , but current tanks are pressurised with cabin air, not vented to ambient

Any gap in insulation blankets beyond an inch or two will make the cabin cold. This is why it is cold around exit doors. Cold air doesn’t get inside through a plug door, but there is area around the door surround that doesn’t have insulation due to the door mechanisms. A huge chunk of floor with no insulation, other than a fuel tank between the floor and outer skin, is going to be uncomfortably cold.

Beyond the coldness factor, the insulation blankets are for fire prevention. They have requirements to withstand a fuel fire for 4 minutes to allow the passengers to escape before the fuselage is penetrated by flames. No insulation blankets between the tank and cabin creates a risk that a fuel fire could quickly go through the floor and enter the cabin before people can evacuate.

pugman211 · Mon Mar 01, 2021 7:59 pm

But doesn't the RCT fuel tank structural integrity require burn through of around 4 minutes anyway?

tealnz · Mon Mar 01, 2021 8:12 pm

Weatherwatcher1 wrote:
It is my understanding that the center fuel tank is outside the pressure vessel of the fuselage. It is my understanding that the A321XLR tank is behind the wheel well. The aft bulkhead of the wheel well is the pressure wall. Am I wrong that the fuel tank being inside the pressure vessel on the A321XLR is what is resulting in additional certification requirements?

To understand this issue we are going to need better technical information on the layout. Meantime, for what it’s worth:

- Leeham in their early reporting on the XLR said that the new RCT would incorporate a void above the gear well as well as two x ACTs worth of hold space aft of the gear well - which implies a complex irregular shape for the RCT

- Leeham also reported that the XLR would require extending the gear bay pressure vessel roof aft over the hold for the length of the two ACTs - which implies that the RCT would be outside the pressure vessel.

Does anyone have any more authoritative info on this?

tomcat · Mon Mar 01, 2021 11:36 pm

tealnz wrote:
Weatherwatcher1 wrote:
It is my understanding that the center fuel tank is outside the pressure vessel of the fuselage. It is my understanding that the A321XLR tank is behind the wheel well. The aft bulkhead of the wheel well is the pressure wall. Am I wrong that the fuel tank being inside the pressure vessel on the A321XLR is what is resulting in additional certification requirements?

To understand this issue we are going to need better technical information on the layout. Meantime, for what it’s worth:

- Leeham in their early reporting on the XLR said that the new RCT would incorporate a void above the gear well as well as two x ACTs worth of hold space aft of the gear well - which implies a complex irregular shape for the RCT

- Leeham also reported that the XLR would require extending the gear bay pressure vessel roof aft over the hold for the length of the two ACTs - which implies that the RCT would be outside the pressure vessel.

Does anyone have any more authoritative info on this?

Indeed Leeham's description implies that the RCT would be outside the pressure vessel. But then, where are located the decompression panels mentioned in the link provide by the thread opener:

Lack of space prevents fitting of compliant panels, while burn-through protection of the cabin floor cannot be comprehensive because decompression panels either side of the fuselage must remain free of insulation panels.

If the new tank is outside the pressure vessel, then there is no more need of decompression panels above it. I must be missing something.

Here are some pictures and explanation of these decompression panels for whoever is not familiar with them:
https://aviation.stackexchange.com/questions/26039/what-are-these-grilles-in-the-passenger-cabin-of-this-787

tomcat · Tue Mar 02, 2021 12:52 am

Here are some pictures to get a better view on the wheel well area and on the cargo compartment details.

This one shows the unequipped wheel well from the outside with the front being on the right side of the picture. Note the transition of the height of the keel beam just aft of the center wingbox:
https://www.rgifrance.fr/fr/actualites/mise-en-service-de-la-machine-d%E2%80%99al%C3%A9sage-keel-beam-poste-15-80

Now the fully equipped wheel well seen from inside. The front is now on the left side of the picture (see the keel beam transition):
https://imgur.com/a/q6EZ8?nc=1

In this article of the NYT, one picture is taken inside the cargo bay before completion:
https://www.nytimes.com/2017/05/03/magazine/a-look-inside-airbuss-epic-assembly-line.html

Pellegrine · Tue Mar 02, 2021 4:32 am

Sounds similar to what the A340-500 went through with its RCT.

WIederling · Tue Mar 02, 2021 8:14 am

Polot wrote:
It would be interesting to know what temperature the floor of the cabin could get to. Jet fuel can get quite cold in flight. Are we talking about your feet experiencing a minor chill in flight or spending 7 hrs at near freezing (water, not jet fuel) temps ?

Center fuel is the first to go, isn't it?

alyusuph · Tue Mar 02, 2021 9:23 am

Airbus is taking the same missteps of the 737. They are milking out every inch of possible fuselage extension, space usage, to get maximum range out of a fuselage which was not designed for its current roles. The A321 will end up being a very heavy aircraft - unnecessarily.

Boeing had an opportunity to innovate the 757 for a new version, they squandered the chance. I think the next generation of narrow bodies should start from where the 757 ended, and nothing below (737/320/1) or above it (A330/B767/788).

Opus99 · Tue Mar 02, 2021 9:30 am

Honestly, I find it very difficult to believe Airbus will not find a reasonable fix for this problem

Noshow · Tue Mar 02, 2021 9:34 am

Nice topic but not many details to base concerns on. Fuel is circulated so no cold fuel should accumulate under the cabin floor. Cold fuel is in the wings not in fuselage tanks.

More like some campaign to throw some mud on the XLR just in case? Sounds like we are in for some more dirty duel?

seahawk · Tue Mar 02, 2021 10:53 am

Anything related to the fuel system should be taken extremely seriously, especially when it comes to burn through protection. Insulation is not a problem imho. In the worst case you use an insulation mat on the cabin floor.

BarrenLucidity · Tue Mar 02, 2021 11:54 am

Opus99 wrote:
zeke wrote:
JerseyFlyer wrote:
I am not clear if this is an issue that has arisen late in the design process or was always anticipated but has just been published.

Its arisen as the fuel tank flammability rules came in after the A321 was designed, however the rules as written do not adequately cover this sort of new feature so they have to go through this process. Every new aircraft these days has large number of these variations as the rules are well behind where the cutting edge R&D is.

Surely this should not be that big of a deal to rectify?

According to the article there is not a straightforward fix. It is definitely impacting many project managers and timelines. The tank is central to the XLR success so it'll be interesting to see how it's resolved. I doubt they get any waiver.

Weatherwatcher1 · Tue Mar 02, 2021 1:32 pm

seahawk wrote:
Anything related to the fuel system should be taken extremely seriously, especially when it comes to burn through protection. Insulation is not a problem imho. In the worst case you use an insulation mat on the cabin floor.

The regulatory authorities take fuel tanks, potential ignition sources and fire prevention extremely seriously. The FAA and EASA can’t even agree on what to do for 50 year old 727 aux tanks

https://www.flightglobal.com/airframers ... 42.article

European regulators are looking into alternative measures to mitigate an apparent safety risk relating to Boeing 727 auxiliary fuel tanks, after opting not to adopt a US FAA directive on the matter.

I don’t see regulatory authorities likely to approve exemptions for the A321XLR to the regulations.

planecane · Tue Mar 02, 2021 1:52 pm

alyusuph wrote:
Airbus is taking the same missteps of the 737. They are milking out every inch of possible fuselage extension, space usage, to get maximum range out of a fuselage which was not designed for its current roles. The A321 will end up being a very heavy aircraft - unnecessarily.

Boeing had an opportunity to innovate the 757 for a new version, they squandered the chance. I think the next generation of narrow bodies should start from where the 757 ended, and nothing below (737/320/1) or above it (A330/B767/788).

Any new version of the 757 would have been heavier than the A321XLR.

The next generation of narrowbodies will likely start a bit bigger than the 737-800/MAX8. There is a need for aircraft under 200 seats and will be for a long time.

FluidFlow · Tue Mar 02, 2021 2:41 pm

There is a clear path outlined by EASA how to make sure the RCT follows certification rules:

Means of Compliance to Special Condition SC-D25.856-01 The associated Means of Compliance is published for awareness only and is not subject to public consultation. In showing compliance to SC-E25.856-01the following may be considered:
1. The strategy for protection of the fuselage against external pool fire effects for a fuselage structural centre tank installation may be demonstrated to be at least as safe as the previous design of the basic aircraft, for which the burnthrough protection was found compliant with CS 25.856(b).
2.The demonstration can be achieved either through the design features of the RCT itself, or through additional design features.
3.The demonstration can be based on tests, analysis supported by test evidence, or design similarity.
4.When flame penetration testing is performed on materials other than insulation blankets that would be compliant to 25.856(b), the test should be carried out in accordance with the test conditions prescribed in Appendix F Part VII with regards to the fire threat with an exposure time of 5 minutes to the flame. There should be no flame penetration during these 5 minutes.

If Airbus can prove this then the RCT is compliant and the XLR is good to go. Seems pretty straight forward. Now it is on to Airbus to make this happen.

It seems that if Airbus can prove that their design withstands external fires long enough (5min) it gives occupants enough time to leave the aircraft in a case of emergency with an external fire.

WayexTDI · Tue Mar 02, 2021 3:00 pm

alyusuph wrote:
Airbus is taking the same missteps of the 737. They are milking out every inch of possible fuselage extension, space usage, to get maximum range out of a fuselage which was not designed for its current roles. The A321 will end up being a very heavy aircraft - unnecessarily.

Boeing had an opportunity to innovate the 757 for a new version, they squandered the chance. I think the next generation of narrow bodies should start from where the 757 ended, and nothing below (737/320/1) or above it (A330/B767/788).

Well, Airbus, and Boeing for that matter, is a for-profit publicly listed company; as such, if they find a way to make money off an existing product because customers buy it, then that's what they do, and have to do.
Remember: they manufacture what sells, it's only when customers stop buying that a product doesn't sell...

astuteman · Tue Mar 02, 2021 3:33 pm

alyusuph wrote:
Airbus is taking the same missteps of the 737. They are milking out every inch of possible fuselage extension, space usage, to get maximum range out of a fuselage which was not designed for its current roles. The A321 will end up being a very heavy aircraft - unnecessarily.

Boeing had an opportunity to innovate the 757 for a new version, they squandered the chance. I think the next generation of narrow bodies should start from where the 757 ended, and nothing below (737/320/1) or above it (A330/B767/788).

I must confess to not understanding this.
Firstly the XLR fuselage is not stretched, or extended, over a standard A321 fuselage.
And currently, to achieve the XLR's 4,700Nm nominal range requires an RCT that weighs the same as an ACT (i.e. 500kg), and about 150kg of wing and landing gear strengthening.
Which means the A321XLR currently will end up weighing the same as a bog standard 3,500Nm A321NEO (which needs an ACT to achieve that range) - within a 150kg delta.

All of which very much refutes your claim about the XLR ending up being "a very heavy aircraft".
The XLR currently will have an OEW easily 10t lower than the 757-200 which it comfortably outranges

The currently unanswered question is what, if any, change in weight this issue will result in. And/or reduction in tank capacity

Rgds

zeke · Tue Mar 02, 2021 3:49 pm

BarrenLucidity wrote:
According to the article there is not a straightforward fix. It is definitely impacting many project managers and timelines. The tank is central to the XLR success so it'll be interesting to see how it's resolved. I doubt they get any waiver.

They are not seeking a waiver, the issue is the design regulations are years behind where industry is, and this sort of process is common where the existing rules don't cover the proposed design features.

This is what triggers special conditions

“The Agency shall prescribe special detailed technical specifications, named special
conditions, for a product, if the related airworthiness code does not contain adequate or
appropriate safety standards for the product, because:
1. The product has novel or unusual design features relative to the design practices on
which the applicable airworthiness code is based; or
2. The intended use of the product is unconventional; or
3. Experience from other similar products in service or products having similar design
features has shown that unsafe conditions may develop.”

from https://www.easa.europa.eu/sites/defaul ... 102010.pdf

seahawk · Tue Mar 02, 2021 4:03 pm

Weatherwatcher1 wrote:
seahawk wrote:
Anything related to the fuel system should be taken extremely seriously, especially when it comes to burn through protection. Insulation is not a problem imho. In the worst case you use an insulation mat on the cabin floor.

The regulatory authorities take fuel tanks, potential ignition sources and fire prevention extremely seriously. The FAA and EASA can’t even agree on what to do for 50 year old 727 aux tanks

https://www.flightglobal.com/airframers ... 42.article

European regulators are looking into alternative measures to mitigate an apparent safety risk relating to Boeing 727 auxiliary fuel tanks, after opting not to adopt a US FAA directive on the matter.

I don’t see regulatory authorities likely to approve exemptions for the A321XLR to the regulations.

And that is good. You do not fool around with fuel systems.

Revelation · Tue Mar 02, 2021 4:26 pm

alyusuph wrote:
Airbus is taking the same missteps of the 737. They are milking out every inch of possible fuselage extension, space usage, to get maximum range out of a fuselage which was not designed for its current roles. The A321 will end up being a very heavy aircraft - unnecessarily.

Airbus is addressing the biggest weakness of the A320 family, its wing was not designed for long range so does not hold the amount of fuel needed for the longer range routes. I think they will find a good solution to meeting the regulator's concerns. It may or may not meet all the targets on weight and capacity, but I doubt it will miss in a meaningful way. Right now the give and take is around "milking" because everyone wants an optimal design but that does not mean anyone will accept compromises on safety.

FluidFlow wrote:
There is a clear path outlined by EASA how to make sure the RCT follows certification rules:

Means of Compliance to Special Condition SC-D25.856-01 The associated Means of Compliance is published for awareness only and is not subject to public consultation. In showing compliance to SC-E25.856-01the following may be considered:
1. The strategy for protection of the fuselage against external pool fire effects for a fuselage structural centre tank installation may be demonstrated to be at least as safe as the previous design of the basic aircraft, for which the burnthrough protection was found compliant with CS 25.856(b).
2.The demonstration can be achieved either through the design features of the RCT itself, or through additional design features.
3.The demonstration can be based on tests, analysis supported by test evidence, or design similarity.
4.When flame penetration testing is performed on materials other than insulation blankets that would be compliant to 25.856(b), the test should be carried out in accordance with the test conditions prescribed in Appendix F Part VII with regards to the fire threat with an exposure time of 5 minutes to the flame. There should be no flame penetration during these 5 minutes.

If Airbus can prove this then the RCT is compliant and the XLR is good to go. Seems pretty straight forward. Now it is on to Airbus to make this happen.

It seems that if Airbus can prove that their design withstands external fires long enough (5min) it gives occupants enough time to leave the aircraft in a case of emergency with an external fire.

That is a path to testing a solution, but not a path to designing a solution, especially not one that meets expectations.

Noshow wrote:
Nice topic but not many details to base concerns on. Fuel is circulated so no cold fuel should accumulate under the cabin floor. Cold fuel is in the wings not in fuselage tanks.

More like some campaign to throw some mud on the XLR just in case? Sounds like we are in for some more dirty duel?

Relax. Some times a cigar is just a cigar.

To me the hoopla being raised is no different than the FUD that was raised here around 779 structural testing "only" achieving 149% of target. Calmer minds will prevail, solutions will be found.

Opus99 · Tue Mar 02, 2021 4:27 pm

https://twitter.com/tpalazzo/status/136 ... 39556?s=21

Yup it’s getting out there now

flipdewaf · Tue Mar 02, 2021 7:17 pm

The moderation on this site is weird!

Revelation wrote:
flipdewaf wrote:
JerseyFlyer wrote:
That sounds right. Airbus would have been aware that the regulatory framework had this gap in it when designing the RCT - I don't think there is need for panic!

Agreed, I think it’s likely that an airframer aware of such a gap wouldn’t first ask how the regulator wants it doing, they would attempt to design something appropriate before approaching the regulator as then the foot is in the door with the power of the incumbent idea.

Seems similar to the procedure followed for 779's folding wingtips. Current regulations didn't cover it "adequately". A set of special conditions were proposed, comments were solicited, responses were formulated, document was updated and released.

I’m working on some new tech in the industry I’m in at the moment and the regulatory environment is working as described here. We don’t have suitable regulations that cover what we are working on as it doesn’t behave as predictable as previous iterations (but it’s lots faster) so we are working with the developers, industry experts, independent auditors and university’s to ensure that suitable methods of test and inspection are done on the final products. In most cases where I work the premise is around demonstrating suitability as I would expect it to be here. Most of the time I would expect some ‘salesmanship’ but on the whole I would expect things to sell on their own merit.

Fred

Sent from my iPad using Tapatalk

atcsundevil · Tue Mar 02, 2021 8:30 pm

flipdewaf wrote:
The moderation on this site is weird!

Several posts were removed because they stemmed from a quoted post that was deleted for a rules violation. I'm required to remove all posts that quote removed posts, so sometimes it can snowball. That's been the policy here for as long as you or I have been users. If you have an issue, please post about it in the Site Related Forum.

✈️ atcsundevil

Weatherwatcher1 · Tue Mar 02, 2021 9:59 pm

zeke wrote:
BarrenLucidity wrote:
According to the article there is not a straightforward fix. It is definitely impacting many project managers and timelines. The tank is central to the XLR success so it'll be interesting to see how it's resolved. I doubt they get any waiver.

They are not seeking a waiver, the issue is the design regulations are years behind where industry is, and this sort of process is common where the existing rules don't cover the proposed design features.

This is what triggers special conditions

“The Agency shall prescribe special detailed technical specifications, named special
conditions, for a product, if the related airworthiness code does not contain adequate or
appropriate safety standards for the product, because:
1. The product has novel or unusual design features relative to the design practices on
which the applicable airworthiness code is based; or
2. The intended use of the product is unconventional; or
3. Experience from other similar products in service or products having similar design
features has shown that unsafe conditions may develop.”

from https://www.easa.europa.eu/sites/defaul ... 102010.pdf

How is a fuel tank not meeting burn through compliance requirements any of those? I don’t see how fuel tank flammability regulations are years behind the industry.

While the panels would prevent passengers above the tank from getting chilled feet, Airbus says there isn’t enough room to install ones that fully meet existing standards for burn-through compliance.

https://www.bloomberg.com/amp/news/arti ... ssion=true

It sounds like the A321XLR cannot meet the burn through requirements due to space constraints with installing the rear center fuel tank. If that’s true, Airbus can either request a special condition for the product or redesign the fuel tank to be compliant with the regulations.

Elkadad313 · Tue Mar 02, 2021 10:36 pm

Revelation wrote:

To me the hoopla being raised is no different than the FUD that was raised here around 779 structural testing "only" achieving 149% of target. Calmer minds will prevail, solutions will be found.

Didn't the A-380 'only' achieve 149%?

BEG2IAH · Wed Mar 03, 2021 4:07 am

https://finance.yahoo.com/news/boeing-c ... 31572.html
Looks like Boeing sent a letter to EASA.

WayexTDI · Wed Mar 03, 2021 5:08 am

Elkadad313 wrote:
Revelation wrote:

To me the hoopla being raised is no different than the FUD that was raised here around 779 structural testing "only" achieving 149% of target. Calmer minds will prevail, solutions will be found.

Didn't the A-380 'only' achieve 149%?

It was the wing that failed between 145 and 150%; that wing was part of the first set of wings, and subsequent ones were "refined" and shown to meet the 150% requirement.

TeamLH · Wed Mar 03, 2021 7:15 am

So Boeing raised safety concerns to EASA. Did this happen before that a manufacturer raised safety concerns to an authoritiy about a product of a competitor?

flipdewaf · Wed Mar 03, 2021 7:55 am

Weatherwatcher1 wrote:

https://www.bloomberg.com/amp/news/arti ... ssion=true

It sounds like the A321XLR cannot meet the burn through requirements due to space constraints with installing the rear center fuel tank. If that’s true, Airbus can either request a special condition for the product or redesign the fuel tank to be compliant with the regulations.

The two safety critical things in that article are:
a. The crashworthiness brought up by Boeing at the initial consultation. This I believe was already addressed by EASA in that it was rejected as being part of the regs.
b.the burn through regulation, this not being met by the standard methods because those standard methods do not fit. It is then not a rubber stamp exercise for airbus to say “we have met the regulation by installing a previously tested and agreed system” but to provide evidence that the new design solution that airbus have also meets the requirements of the regulation, this will likely need further evidence which could require physical fire testing to demonstrate compliance. The regulators aren’t stupid enough to mandate specific design solutions, that opens them up to a world of litigation, the require demonstration of outcomes.

Fred

Sent from my iPhone using Tapatalk

FluidFlow · Wed Mar 03, 2021 8:03 am

flipdewaf wrote:
Weatherwatcher1 wrote:

https://www.bloomberg.com/amp/news/arti ... ssion=true

It sounds like the A321XLR cannot meet the burn through requirements due to space constraints with installing the rear center fuel tank. If that’s true, Airbus can either request a special condition for the product or redesign the fuel tank to be compliant with the regulations.

The two safety critical things in that article are:
a. The crashworthiness brought up by Boeing at the initial consultation. This I believe was already addressed by EASA in that it was rejected as being part of the regs.
b.the burn through regulation, this not being met by the standard methods because those standard methods do not fit. It is then not a rubber stamp exercise for airbus to say “we have met the regulation by installing a previously tested and agreed system” but to provide evidence that the new design solution that airbus have also meets the requirements of the regulation, this will likely need further evidence which could require physical fire testing to demonstrate compliance. The regulators aren’t stupid enough to mandate specific design solutions, that opens them up to a world of litigation, the require demonstration of outcomes.

Fred

Sent from my iPhone using Tapatalk

EASA already outlined exactly that:

Means of Compliance to Special Condition SC-D25.856-01 The associated Means of Compliance is published for awareness only and is not subject to public consultation. In showing compliance to SC-E25.856-01the following may be considered:
1. The strategy for protection of the fuselage against external pool fire effects for a fuselage structural centre tank installation may be demonstrated to be at least as safe as the previous design of the basic aircraft, for which the burnthrough protection was found compliant with CS 25.856(b).
2.The demonstration can be achieved either through the design features of the RCT itself, or through additional design features.
3.The demonstration can be based on tests, analysis supported by test evidence, or design similarity.
4.When flame penetration testing is performed on materials other than insulation blankets that would be compliant to 25.856(b), the test should be carried out in accordance with the test conditions prescribed in Appendix F Part VII with regards to the fire threat with an exposure time of 5 minutes to the flame. There should be no flame penetration during these 5 minutes.

So the tank or the tank with additional features has to meet this criteria.

Boeing raised two concerns, both got dismissed. It seems all this news outlets are just reading the EASA publications and make stories out of it. The goal posts are set and it is now up to Airbus to prove that their design meets the criteria set by the regulator.

EDIT: Here is the official EASA source:

https://www.easa.europa.eu/sites/default/files/dfu/sc-d25.856-01_issue-01_-_final_post_consultation_0.pdf

https://www.easa.europa.eu/sites/default/files/dfu/crd_-_sc-d25.856-01_issue-01_0.pdf

marcelh · Wed Mar 03, 2021 8:21 am

FluidFlow wrote:
Boeing raised two concerns, both got dismissed. It seems all this news outlets are just reading the EASA publications and make stories out of it. The goal posts are set and it is now up to Airbus to prove that their design meets the criteria set by the regulator.

So Boeing did made a statement in the first place about the safety of the A321XLR...

FluidFlow · Wed Mar 03, 2021 8:32 am

marcelh wrote:
FluidFlow wrote:
Boeing raised two concerns, both got dismissed. It seems all this news outlets are just reading the EASA publications and make stories out of it. The goal posts are set and it is now up to Airbus to prove that their design meets the criteria set by the regulator.

So Boeing did made a statement in the first place about the safety of the A321XLR...

It is all here, comment 2 and 3 are from Boeing and the EASA answer:

https://www.easa.europa.eu/sites/default/files/dfu/crd_-_sc-d25.856-01_issue-01_0.pdf

flipdewaf · Wed Mar 03, 2021 8:58 am

FluidFlow wrote:
flipdewaf wrote:
Weatherwatcher1 wrote:

https://www.bloomberg.com/amp/news/arti ... ssion=true

It sounds like the A321XLR cannot meet the burn through requirements due to space constraints with installing the rear center fuel tank. If that’s true, Airbus can either request a special condition for the product or redesign the fuel tank to be compliant with the regulations.

The two safety critical things in that article are:
a. The crashworthiness brought up by Boeing at the initial consultation. This I believe was already addressed by EASA in that it was rejected as being part of the regs.
b.the burn through regulation, this not being met by the standard methods because those standard methods do not fit. It is then not a rubber stamp exercise for airbus to say “we have met the regulation by installing a previously tested and agreed system” but to provide evidence that the new design solution that airbus have also meets the requirements of the regulation, this will likely need further evidence which could require physical fire testing to demonstrate compliance. The regulators aren’t stupid enough to mandate specific design solutions, that opens them up to a world of litigation, the require demonstration of outcomes.

Fred

Sent from my iPhone using Tapatalk

EASA already outlined exactly that:

Means of Compliance to Special Condition SC-D25.856-01 The associated Means of Compliance is published for awareness only and is not subject to public consultation. In showing compliance to SC-E25.856-01the following may be considered:
1. The strategy for protection of the fuselage against external pool fire effects for a fuselage structural centre tank installation may be demonstrated to be at least as safe as the previous design of the basic aircraft, for which the burnthrough protection was found compliant with CS 25.856(b).
2.The demonstration can be achieved either through the design features of the RCT itself, or through additional design features.
3.The demonstration can be based on tests, analysis supported by test evidence, or design similarity.
4.When flame penetration testing is performed on materials other than insulation blankets that would be compliant to 25.856(b), the test should be carried out in accordance with the test conditions prescribed in Appendix F Part VII with regards to the fire threat with an exposure time of 5 minutes to the flame. There should be no flame penetration during these 5 minutes.

So the tank or the tank with additional features has to meet this criteria.

Boeing raised two concerns, both got dismissed. It seems all this news outlets are just reading the EASA publications and make stories out of it. The goal posts are set and it is now up to Airbus to prove that their design meets the criteria set by the regulator.

EDIT: Here is the official EASA source:

https://www.easa.europa.eu/sites/default/files/dfu/sc-d25.856-01_issue-01_-_final_post_consultation_0.pdf

https://www.easa.europa.eu/sites/default/files/dfu/crd_-_sc-d25.856-01_issue-01_0.pdf

Apologies, I did read your post previously and thats where the information became lodged in my head. Thanks for the links again.

It seems that like the 779X fuselage blowout its the media and the opposing fanboys sensationalising it, no doubt we'll see it pop up on simple flying and verovenia next week as the most important news this century.

Fred

FluidFlow · Wed Mar 03, 2021 9:06 am

flipdewaf wrote:
FluidFlow wrote:
flipdewaf wrote:
The two safety critical things in that article are:
a. The crashworthiness brought up by Boeing at the initial consultation. This I believe was already addressed by EASA in that it was rejected as being part of the regs.
b.the burn through regulation, this not being met by the standard methods because those standard methods do not fit. It is then not a rubber stamp exercise for airbus to say “we have met the regulation by installing a previously tested and agreed system” but to provide evidence that the new design solution that airbus have also meets the requirements of the regulation, this will likely need further evidence which could require physical fire testing to demonstrate compliance. The regulators aren’t stupid enough to mandate specific design solutions, that opens them up to a world of litigation, the require demonstration of outcomes.

Fred

Sent from my iPhone using Tapatalk

EASA already outlined exactly that:

Means of Compliance to Special Condition SC-D25.856-01 The associated Means of Compliance is published for awareness only and is not subject to public consultation. In showing compliance to SC-E25.856-01the following may be considered:
1. The strategy for protection of the fuselage against external pool fire effects for a fuselage structural centre tank installation may be demonstrated to be at least as safe as the previous design of the basic aircraft, for which the burnthrough protection was found compliant with CS 25.856(b).
2.The demonstration can be achieved either through the design features of the RCT itself, or through additional design features.
3.The demonstration can be based on tests, analysis supported by test evidence, or design similarity.
4.When flame penetration testing is performed on materials other than insulation blankets that would be compliant to 25.856(b), the test should be carried out in accordance with the test conditions prescribed in Appendix F Part VII with regards to the fire threat with an exposure time of 5 minutes to the flame. There should be no flame penetration during these 5 minutes.

So the tank or the tank with additional features has to meet this criteria.

Boeing raised two concerns, both got dismissed. It seems all this news outlets are just reading the EASA publications and make stories out of it. The goal posts are set and it is now up to Airbus to prove that their design meets the criteria set by the regulator.

EDIT: Here is the official EASA source:

https://www.easa.europa.eu/sites/default/files/dfu/sc-d25.856-01_issue-01_-_final_post_consultation_0.pdf

https://www.easa.europa.eu/sites/default/files/dfu/crd_-_sc-d25.856-01_issue-01_0.pdf

Apologies, I did read your post previously and thats where the information became lodged in my head. Thanks for the links again.

It seems that like the 779X fuselage blowout its the media and the opposing fanboys sensationalising it, no doubt we'll see it pop up on simple flying and verovenia next week as the most important news this century.

Fred

No need to apologize, I miss a lot of stuff as well and am happy if it is pointed out again.

I understand, that there is speculation about the abilities of Airbus being able to get the design certified within their promised time frame and promised specifications but there really is too much stuff written, that is far off from what actually is going on.

As you mentioned I see the same thing happening again as with the 779X (or the MAX-10). The certification criteria is known and the manufacturers know what to do. Boeing admitted they need more time to reach them goals but that is nothing sensational nor do I think Boeing or Airbus cant reach them targets. Sometimes it takes more time but both manufacturers are capable.

The media just seems bored and makes up big troubles out of something that is not, or not yet, as we have no answer from Airbus as of if the certification criteria can be met.

mxaxai · Wed Mar 03, 2021 9:48 am

FluidFlow wrote:
It is all here, comment 2 and 3 are from Boeing and the EASA answer:

https://www.easa.europa.eu/sites/default/files/dfu/crd_-_sc-d25.856-01_issue-01_0.pdf

Brief excerpt of Boeing's main concerns in case anybody does not want to / cannot open the pdf file:

Fuel tanks integral to the airframe structure inherently provide less
redundancy than structurally separate fuel tanks. Such integral fuel
tanks located within the fuselage volume can foreseeably result in
more hazardous outcomes when exposed to threats such as an
external pool-fed fire.

Boeing is concerned about other risks as identified in this paragraph.
The inclusion of an auxiliary fuel tank integral to the fuselage
presents many potential hazards, particularly the protection against
structural disruption due to an otherwise survivable off-runway or
landing gear failure event. Many of these hazards have been
addressed in the past per the advisory material in FAA Advisory
Circular (AC) 25-8 or other equivalent guidance.

EASA promises to ensure that the design is sufficiently resistant to both external fires and structural loads during runway excursions or landing gear failures, though they don't intend to change the text of this particular Special Condition.

---------------
One could accuse Boeing of making life unneccesarily hard for Airbus but I think they'll benefit directly from any new regulations. Clearly, there is some risk that is not fully covered by existing regulations. If Boeing ever wanted to develop a similar fuel tank design, they'd run into the same problems. Now that the risk is being assessed and new regulations ("special condition") are being developed, Boeing can use this as a blueprint on how to certify their own design.

If Airbus manages to get an unsafe design certified and Boeing subsequently uses similar designs, or vice versa, a grounding would affect both manufacturers.

sxf24 · Wed Mar 03, 2021 12:49 pm

TeamLH wrote:
So Boeing raised safety concerns to EASA. Did this happen before that a manufacturer raised safety concerns to an authoritiy about a product of a competitor?

Yes.

Weatherwatcher1 · Wed Mar 03, 2021 1:03 pm

I find it really interesting to learn more about the inner workings of manufacturers and regulatory authorities to ensure airplanes are safe. It’s truly amazing the level of analysis that goes into demonstrating compliance as well as the thought process behind each requirement. It puts into context what the engineers at the FAA and EASA do. It’s not all about grandfathering designs to meet outdated regulations like some want us to believe.

jeffrey0032j · Wed Mar 03, 2021 1:41 pm

If anyone knows about burning fuel tanks, it would be Boeing, so they do have the painful experience and knowledge to be qualified to raise such a concern.

zeke · Wed Mar 03, 2021 1:49 pm

Weatherwatcher1 wrote:
How is a fuel tank not meeting burn through compliance requirements any of those?

Simply because since the new rules were brought into force there has been no tank of this sort of design feature certified. Tanks have either been fully enclosed within the wing, or fully enclosed within the cargo hold.

The A321 (since the beginning) does not have fuel pumps within the centre tank, it has "jet pumps" which essentially use motive flow to syphon fuel from the tank.

Opus99 · Wed Mar 03, 2021 2:10 pm

https://www.reuters.com/article/us-airb ... SKCN2AU2RJ

“Commercial stakes are also high.

One industry source familiar with the project warned any extended wrangle over certification could delay the A321XLR's service entry from "late 2023" to 2024 or beyond.

Should that happen, sources say Boeing is expected to encourage airlines to wait a few years longer for a potential all-new model that insiders say would leapfrog the A321XLR.”

Of course. Boeing will milk out ANY opportunity they get.

This is going to be interesting

seahawk · Wed Mar 03, 2021 2:14 pm

Opus99 wrote:
https://www.reuters.com/article/us-airbus-design-boeing-idUSKCN2AU2RJ

“Commercial stakes are also high.

One industry source familiar with the project warned any extended wrangle over certification could delay the A321XLR's service entry from "late 2023" to 2024 or beyond.

Should that happen, sources say Boeing is expected to encourage airlines to wait a few years longer for a potential all-new model that insiders say would leapfrog the A321XLR.”

Of course. Boeing will milk out ANY opportunity they get.

This is going to be interesting

That has nothing to do with Boeing. Airbus just needs to show that the new tank solution has a protection level equal to or better than the ACTs. And there is no reason at all to demand less.

Opus99 · Wed Mar 03, 2021 2:16 pm

seahawk wrote:
Opus99 wrote:
https://www.reuters.com/article/us-airbus-design-boeing-idUSKCN2AU2RJ

“Commercial stakes are also high.

One industry source familiar with the project warned any extended wrangle over certification could delay the A321XLR's service entry from "late 2023" to 2024 or beyond.

Should that happen, sources say Boeing is expected to encourage airlines to wait a few years longer for a potential all-new model that insiders say would leapfrog the A321XLR.”

Of course. Boeing will milk out ANY opportunity they get.

This is going to be interesting

That has nothing to do with Boeing. Airbus just needs to show that the new tank solution has a protection level equal to or better than the ACTs. And there is no reason at all to demand less.

I mean of course. They should not demand less; I’m just saying Boeing might see an opportunity here to push forward their own jet on the idea that the XLR might be late

seahawk · Wed Mar 03, 2021 2:19 pm

Opus99 wrote:
seahawk wrote:
Opus99 wrote:
https://www.reuters.com/article/us-airbus-design-boeing-idUSKCN2AU2RJ

“Commercial stakes are also high.

One industry source familiar with the project warned any extended wrangle over certification could delay the A321XLR's service entry from "late 2023" to 2024 or beyond.

Should that happen, sources say Boeing is expected to encourage airlines to wait a few years longer for a potential all-new model that insiders say would leapfrog the A321XLR.”

Of course. Boeing will milk out ANY opportunity they get.

This is going to be interesting

That has nothing to do with Boeing. Airbus just needs to show that the new tank solution has a protection level equal to or better than the ACTs. And there is no reason at all to demand less.

I mean of course. They should not demand less; I’m just saying Boeing might see an opportunity here to push out the XLRs certification but let’s see

That obviously is in Boeing´s best interest, but their input changed nothing. What EASA demands is a straight forward requirement and it needs to be enforced.

zeke · Wed Mar 03, 2021 2:20 pm

Opus99 wrote:
Should that happen, sources say Boeing is expected to encourage airlines to wait a few years longer for a potential all-new model that insiders say would leapfrog the A321XLR.”

Of course. Boeing will milk out ANY opportunity they get.

Boeing is not a stakeholder at all in this process, I would suggest you go back and have a look at comments made by Airbus regarding the 787 special conditions. They are considered like any others, however in the end of the day they are not a party to the process or outcome.

A lot of ignorance (probably deliberate by the media to enhance sales and clicks) of the what is actually going on here, I have posted the EASA process above for special conditions. It is a process, not a roadblock.

Opus99 · Wed Mar 03, 2021 2:26 pm

zeke wrote:
Opus99 wrote:
Should that happen, sources say Boeing is expected to encourage airlines to wait a few years longer for a potential all-new model that insiders say would leapfrog the A321XLR.”

Of course. Boeing will milk out ANY opportunity they get.

Boeing is not a stakeholder at all in this process, I would suggest you go back and have a look at comments made by Airbus regarding the 787 special conditions. They are considered like any others, however in the end of the day they are not a party to the process or outcome.

A lot of ignorance (probably deliberate by the media to enhance sales and clicks) of the what is actually going on here, I have posted the EASA process above for special conditions. It is a process, not a roadblock.

I guess Boeing is hoping Airbus will take some time to prove their design meets the special condition? I mean I’ve seen Boeing’s input does not change the special condition but my thing is won’t Airbus have known this from jump also?

JonesNL · Wed Mar 03, 2021 3:16 pm

flipdewaf wrote:
FluidFlow wrote:
flipdewaf wrote:
The two safety critical things in that article are:
a. The crashworthiness brought up by Boeing at the initial consultation. This I believe was already addressed by EASA in that it was rejected as being part of the regs.
b.the burn through regulation, this not being met by the standard methods because those standard methods do not fit. It is then not a rubber stamp exercise for airbus to say “we have met the regulation by installing a previously tested and agreed system” but to provide evidence that the new design solution that airbus have also meets the requirements of the regulation, this will likely need further evidence which could require physical fire testing to demonstrate compliance. The regulators aren’t stupid enough to mandate specific design solutions, that opens them up to a world of litigation, the require demonstration of outcomes.

Fred

Sent from my iPhone using Tapatalk

EASA already outlined exactly that:

Means of Compliance to Special Condition SC-D25.856-01 The associated Means of Compliance is published for awareness only and is not subject to public consultation. In showing compliance to SC-E25.856-01the following may be considered:
1. The strategy for protection of the fuselage against external pool fire effects for a fuselage structural centre tank installation may be demonstrated to be at least as safe as the previous design of the basic aircraft, for which the burnthrough protection was found compliant with CS 25.856(b).
2.The demonstration can be achieved either through the design features of the RCT itself, or through additional design features.
3.The demonstration can be based on tests, analysis supported by test evidence, or design similarity.
4.When flame penetration testing is performed on materials other than insulation blankets that would be compliant to 25.856(b), the test should be carried out in accordance with the test conditions prescribed in Appendix F Part VII with regards to the fire threat with an exposure time of 5 minutes to the flame. There should be no flame penetration during these 5 minutes.

So the tank or the tank with additional features has to meet this criteria.

Boeing raised two concerns, both got dismissed. It seems all this news outlets are just reading the EASA publications and make stories out of it. The goal posts are set and it is now up to Airbus to prove that their design meets the criteria set by the regulator.

EDIT: Here is the official EASA source:

https://www.easa.europa.eu/sites/default/files/dfu/sc-d25.856-01_issue-01_-_final_post_consultation_0.pdf

https://www.easa.europa.eu/sites/default/files/dfu/crd_-_sc-d25.856-01_issue-01_0.pdf

Apologies, I did read your post previously and thats where the information became lodged in my head. Thanks for the links again.

It seems that like the 779X fuselage blowout its the media and the opposing fanboys sensationalising it, no doubt we'll see it pop up on simple flying and verovenia next week as the most important news this century.

Fred

Like clockwork, there is already an article on Verovenia...

astuteman · Wed Mar 03, 2021 3:19 pm

Opus99 wrote:
zeke wrote:
Opus99 wrote:
Should that happen, sources say Boeing is expected to encourage airlines to wait a few years longer for a potential all-new model that insiders say would leapfrog the A321XLR.”

Of course. Boeing will milk out ANY opportunity they get.

Boeing is not a stakeholder at all in this process, I would suggest you go back and have a look at comments made by Airbus regarding the 787 special conditions. They are considered like any others, however in the end of the day they are not a party to the process or outcome.

A lot of ignorance (probably deliberate by the media to enhance sales and clicks) of the what is actually going on here, I have posted the EASA process above for special conditions. It is a process, not a roadblock.

I guess Boeing is hoping Airbus will take some time to prove their design meets the special condition? I mean I’ve seen Boeing’s input does not change the special condition but my thing is won’t Airbus have known this from jump also?

It's probably a bit of a stretch to suggest that, just because this has only now appeared in the press, that dialogue wasn't ongoing much earlier, possibly as early as the inception of the RCT idea in the first place......

You never know, Airbus might by now be within a spit of demonstrating compliance in line with the schedule activity laid out in the project plan for exactly that.
Just because it doesn't appear in the press........

Who knows?

Rgds

zeke · Wed Mar 03, 2021 3:21 pm

Opus99 wrote:
I guess Boeing is hoping Airbus will take some time to prove their design meets the special condition? I mean I’ve seen Boeing’s input does not change the special condition but my thing is won’t Airbus have known this from jump also?

I fail to see how you can turn this into an AvB thread when literally it’s Airbus seeking certification of an existing airframe, this has nothing to do with Boeing.

FluidFlow · Wed Mar 03, 2021 3:24 pm

Revelation wrote:
FluidFlow wrote:
Boeing raised two concerns, both got dismissed.

I think the word you are looking for is "agreed", not "dismissed". Check your PDFs, that's the word you will find in the "EASA comment disposition" column. In essence the comments were deemed redundant rather than incorrect.

You are right. As English is not my mother tongue I sometimes lack the vocabulary. EASA already addressed the concerns from Boeing in their assessment so the comments from Boeing were already implemented into the certification criteria.

Weatherwatcher1 · Wed Mar 03, 2021 3:34 pm

Opus99 wrote:
zeke wrote:
Opus99 wrote:
Should that happen, sources say Boeing is expected to encourage airlines to wait a few years longer for a potential all-new model that insiders say would leapfrog the A321XLR.”

Of course. Boeing will milk out ANY opportunity they get.

Boeing is not a stakeholder at all in this process, I would suggest you go back and have a look at comments made by Airbus regarding the 787 special conditions. They are considered like any others, however in the end of the day they are not a party to the process or outcome.

A lot of ignorance (probably deliberate by the media to enhance sales and clicks) of the what is actually going on here, I have posted the EASA process above for special conditions. It is a process, not a roadblock.

I guess Boeing is hoping Airbus will take some time to prove their design meets the special condition? I mean I’ve seen Boeing’s input does not change the special condition but my thing is won’t Airbus have known this from jump also?

I think both Boeing and Airbus want regulations and special conditions that are feasible to meet while ensuring the worldwide fleet is safe. There are many times both Airbus and Boeing come together with regulatory authorities. Fuel tank ignition, flammability reduction and fire prevention affect all manufacturers.

Pan Am 214 changed the industry in the 1960s regarding fuel tank ignition: https://reports.aviation-safety.net/196 ... N709PA.pdf

British Airtours 28 further changed the industry regarding evacuations, firefighting and interior flammability https://www.bbc.com/news/uk-england-manchester-33304675

We’ve all probably heard of TWA 800 regarding fuel tank ignition. Singapore 6 and China Airlines 120 provided lessons from fuel fires and preventing flames from entering the cabin. Those events all happened on Boeing airplanes. Everyone can learn from them.

Nowadays we have worldwide collaboration so learnings from one manufacturer are shared in the industry. Boeing has much more history than Airbus from the earlier days of the jet age. The engineering teams want to work together. It isn’t about trying to slow down and hurt the competition from a marketing & sales perspective.

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