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Thanks for the comments Gentlemen, the AC link was a big help. Exactly, the problem lies in the process, bonding is like baking, the result varies and depends on the baker, repairs done by an Airline in deep Timbuktoo will produce another result than a “professional” MRO following lab standards...

Bonded doubler repairs to composites, carbon or glass must be justified considering the failure case, i.e depending on the structure classification the component must be able to carry limit or ultimate loading without the repair. Does the same hold true for metal to metal repair? I mean bonded...

@RB Thanks, there’s never a dumb answer only a dumb question. There’s a definition in the (Airbus) SRM (I haven’t bothered to look in Boeing’s) which more or less agrees with what you said, but as CS 25 references “Primary Structure” I wanted an “Authority” reference. I never though to look in...

Two questions really, No. 1, CS-25 (yeah I’m in Euro Land) makes no mention of “Secondary Structure” but does refer (but not define)to “Primary Structure” Can anybody quote me the definition and origin of Primary and Secondary Structure which doesn’t come from the SRM? FAR regs would be...

Hallo Airbus will tell you that you require a minimum cylindrical portion of 0,4 mm in the sheet. For example a 4 mm dia NAS 1097 has a head height of about 1,0 mm, so the minimum skin thickness is 1,4 for that fastener. A cylindrical portion of 0,2 mm will reduce the fatigue life by 25% (ref...

I would tend to use the material allowable for the base thickness, i.e. before chem. milling or other type of processing. If there were any doubts however which one you should be using, you could always stay safe and take the larger of the two values for say, the structure before repair and use...

The easiest and safest way is to get in touch with Airbus product support in Toulouse. If necessary I can pm you the telephone number, but really if you’re working with Airbus aircraft you should have the number.

Thanks for all your posts, they’ve been a great help. The problem I have is we get repairs for Airbus aircraft which we should approve, but the airline has used Boeing Bacs. The allowables that we have are for HLs or Dan. Usually what happens is we get back to the airline and ask for the spec...

Alex. I slight misunderstanding, I wasn’t talking about the doubler, I meant the original structure, which you obviously can’t change, unless you’re thinking of hot-bonding a doubler to it. As to the reasons: Progressively bend the fuselage so as to develop tension in the upper shell and...

Interesting to hear that you are all happy using Ftu. If you assume your structure is working at Ftu you cannot put any holes in it for fasteners etc. It breaks. As regards the Boeing course, the Airbus course says it’s ok to use Fty as the applied ultimate stress for skin repairs, i.e. the...

Does anyone have experience repairing glare fuselage panels? I was wondering if it is possible to cold work fastener holes. We do it now and again (on “normal” 2024) to improve the fatigue life in repaired areas.

Thanks Sean, that is my problem, I receive the repair drawing telling me they have used BAC whatever on an Airbus and we have no real cross reference, apart from what you can put together unofficially, and working for Airbus, I don’t have access to Boeing standards manuals.

Thanks for both your answers, they were both a great help, by the way, can you please tell me on which type of aircraft you work on?

I am currently working for what used to be Focke Wulf (I know they didn’t build the Me 109) in Bremen, Germany. We are at present doing restoration work on a FW Condor. If you give me some examples of the designations that you have maybe I can help.

I agree 1.5 times the limit load is the ultimate load in the aircraft. What I am saying is that the stress produced from 1.5 times the limit load will not exceed the material Fty if we are talking about the fuselage (thin walled tube) structure. See reasons given above. I am also talking about...

Just noticed, nobody has commented on the fact that you cannot put holes in an item that is already working to Ftu, which makes the Ftu method invalid.

Sorry, but I am still not convinced that using Ftu is the only way and most of the posts do say that they find the method conservative. Regarding using 2 doublers instead of 1 with steps etc, you have to remember the 2 doubler solution has a different bending stiffness than 1 thick doubler...

Can anyone please give me an idea of how the typical large passenger aircraft is checked structurally? e.g. when the check is made (FC / FH) and what is done at this check.

Thanks debarra I have a BACB30NW fastener, I only have the spec for a cres BACB30 (the letter code is in the office) The NW Is probably Ti. It’s a problem I have often as the Airbus SRM calls out HL fasteners, there’s a conversion in Chapter 51 but only includes DAN, FoN and such. It’s a shame...

Thanks for both your replies astroclone and inertia4u but I don’t want to have to design always on the conservative side, sometimes it is not possible to put in that 4th fastener (the fatigue guys I’ve met tell me, that 4th fastener wont help him much anyway. I have some Airbus RAG curves that...