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Aircraft edge distance

Aircraft edge distance

Aircraft edge distance

I am looking for an Industry standard that calls out the edge distance of fasteners. I was wondering if there is anyone out there who may know of the spec?


RE: Aircraft edge distance

That would have to be worked out relative to the stresses expected at that joint.

RE: Aircraft edge distance

industry standard edge distance is 2D, measured from the center of the hole.  i use 2D+0.05" to allow some tolerance on installation.  i use the shank diameter (and not the CSK diameter).  this can be relaxed if there isn't a large load applied normal to the edge (if most of the load is applied parallel to the edge; 1.5D would be a minimum (for sheet metal structure).

Lugs are different and typically have smaller ED.

RE: Aircraft edge distance

I recall using a distance of 2 times the diameter for the edge distance.  This was a general rule used to check design.

RE: Aircraft edge distance

The general standard in the industry for metals parts is 2D + 0.05";  For composite parts it is 2.5D + 0.05".

RE: Aircraft edge distance

When you start thinking about creeping closer to the edge on edge distances, start thinking about the De Havilland  Comet.

RE: Aircraft edge distance

Thanks guys. I appreciate the help. I know that at Boeing I think we used 2D + .062 and composites 2.5D +062 same as SWComosites pointed out. The reason for the question was that someone here said that there was an Industry standard out there that could be referenced. I was not sure so I went to the experts.

Thanks again,


RE: Aircraft edge distance

This seems to be more company driven but it is mostly the same.

2D+.050 is the current Boeing standard for design.  Way back when it was 1.7D for load running parallel to the edge if no buckling occurs.  I do routinely see 1.5D on older designs from the 50 to mid 60's designs.

If I recall correctly Douglas used 2D+.030 regardless of load direction.

Liaison Engineering will routinely drop it to 2D because most of the material fastener allowables are taken from 2D.  But this should not be a good rule of thumb for design practices.  Some of the bearing allowables are higher than a 2D material shear out allowable.

RE: Aircraft edge distance

VDI 2230?

RE: Aircraft edge distance

WhiteRabbit (Aerospace)
1.5D used to be the standard edge distance for metals in the 1950s.
Following the Comet disasters, it was changed in Great Britain to a minimum of 2D. I believe most other aircraft manufacturers followed suit.

RE: Aircraft edge distance


MIL-HDBK-5 [MMPDS] allowables for most metals show FBru & FBry in terms of 2.0 (= 2D edge margin) and 1.5 (= 1.5D edge margin) ... see for Yourself... the differences in bearing-tear-out/yield allowables are significant!

The classic "2D +(factor)" equation insures a minimum 2D edge spacing for the nominal diameter fastener... and some accounting for AT LEAST the 2nd oversize (0.032) repair fastener... plus some typical maufacturing "wiggle-room". Typically the "factor" is 0.050 or 0.060... although I have see as littles as 0.030.

Note: on some old Boeing military Acft, an edge margin of 1.7D + 0.030-0.06" was routinely used in design. In-real-world practice, this often drifted down to 1.7D for typical production installation tolerances. Repairs with a starting 1.7D fastener egde margin, really get dicy for the liaison and stress guys when oversized fasteners are required... and gets even worse with thin-skins and deep-countersinks!

My preference is definitely 2D + 0.06"!!!

Regards, Wil Taylor

RE: Aircraft edge distance

2D edge margin is fine pretty much across the board.

The Comet was way more than just EM.

Bear in mind though that Boeing being the rebels they are have the same definition for edge Margin (EM) as everyone else in industry uses for edge Distance (ED).

Boeing uses a tolerance of plus minus 0.030" for production.  So a worst case you have 1.7EM which would drive a repair on existing structure to say 1.5EM min.  I have routinely had Boeing approve as low as 1.5EM on structure, skins 1.7EM.

Now the allowables in MMPDS are great.  It is my experience that statically it is not an issue, of course depending on all the appropriate caveats.  It is the fatigue portion.  at 2D the run out is nearly infinite at 1.7 it is exponential and at 1.5 it is worth review.  With special procedures for hole quality, zero timing, inspections, life limits, 1.2 can be fine.

If you are so close statically the EM is an issue you won't cut it for fatigue.

RE: Aircraft edge distance

There is a difference between Edge Margin and Edge Distance.

Interestingly enough, Boeing has messed this up with the integration of Douglas products.
Examples are the DC-9/MD-80 SRM and the 737 SRM definitions of Edge Distance vs Edge Margin. The figure is almost identical, but the description of the measurement is Opposite. This brought a "UHHH, we'll get back to you" response from Boring Tech Support after a Repair Submission was disapproved for short ED.
Old Douglas Engineer submitting to Boeing Engineering.

I know what you mean. But have seen both terms used here.
Even in the ar-mmpds-01 manual both terms are used without an explaination of exactly where the dimension is measured.
Assumed all measurement from the center of the fastener location.  (or am I still confused?)


RE: Aircraft edge distance

you're correct, edge distance is measured from the hole CL.

edge margin ?

RE: Aircraft edge distance

I am the old Douglas goat that submitted a repair to Boeing ESE that my partner rerig mentioned above. When I deal with the engineers that reside in the hallowed halls on top of "Mount Boeing" I use their engineering terminology as a profesional courtesy. I used edge margin of 1.5 measured from the edge of the hole to E.O.P. in my repair scheme. After the usual 5 day wait they sent me a responce that my E.M. of 1.5 was unacceptable, and I was to use an E.M. of 2.0. I looked in Chp 51 in the SRM and sure enough E.M. had been changed from 1.5 to 2.0 and now measured from the center of the hole. When did this change occur? Well shame on me for not checking the SRM (my goof) I was even more surprised when I looked at my trusty (and current) DC-9/MD-80 SRM and found 2.0 ED measured from the center of the as it has always been done. I copied both documents to .pdf file and sent to ESE. Rerig accuratly described the response. So currently Boeing North uses 2.0 EM measured from the center of the hole and calls ED the distance from the edge of the hole to EOP. Boeing South uses 2.0 ED measured from the center of the hole and call EM the distance from the edge of the hole to the EOP. Yep, same company. I'm not trying to kick Boeing in the knees, but for a company that prides itself in engineering excellance and lets you know about it every time they get the chance........What the heck?         

RE: Aircraft edge distance

whales ... aim higher (with your kick !)

RE: Aircraft edge distance

Bombardier Strength Manual States:

Protruding head               

Edge margins - minimum   1½ (fastener dia)  
               preferred 2 (fastener dia)

Countersunk head

Edge margins - minimum  2 (fastener dia)
               preferred 2½ (fastener dia)

" and e is the edge distance measured from the hole centre to the edge of the material in the direction of applied stress."

As pointed out previously there is no definition for 'edge margin' in this manual.

IMHO Fastener edge distance / margin is a fairly basic thing, this should be exceptionally clear-cut across aircraft industries and countries!

RE: Aircraft edge distance

How about a Mil spec for your reference?  It's MIL-R-47196, "RIVETS, BUCK TYPE, PREPARATION FOR AND INSTALLATION OF (Superseded by NASM47196)", available from the ASSIST website.  A very convenient thing to call up on a drawing - I suspect that's the purpose of Mrcadman2u's question.

Edge distances and terminology are spelled out in detail in the spec, and it's public domain.  It is interesting to note that even in the standard, the allowable "edge margins", as they call them, are also subjective.  The allowable margins are different depending on rivet head type, dimpling, and inspectability.  Since the document dates from 1977, my guess is that the authors could have drawn from many sources, whose data had been refined over many years.

Mind you, there is a passage that goes something like: "edge margins less than those specified above requires further engineering approval", which is sorta what everyone else here is talking about.

There may also be guidance in Advisory Circular AC65-12, though I haven't got a copy handy to look it up.  There is a very large and comprehensive section about riveting.

In any event, if one is going to specify a <2D edge distance, one will be venturing into the "non-standard" territory, as everyone has already pointed out.

Steven Fahey, CET

RE: Aircraft edge distance


AC65 12 is "[Large AC] Airframe and Powerplant Mechanics Powerplant Handbook" ... is that the one you meant ?

maybe AC43 13-1, chapter 4, section 4 ... there is a small paragraph on ed, in a nice section on riveting ("all you wanted to know ...")

RE: Aircraft edge distance

to follow up on sparweb's mil spec ... (geez isn't ASSIST a fantastic source of data) ... you have to download the superceded MIL-R-47196, as you have to buy the NASM-47196 from the AIAA.

and not to bash Bombardier, but does anyone else consider the CSK in edge distance ? ... it's an interesting statement as i'm sure (from personal knowledge) that all previous designs would have used 2D.  doesn't it create liability issues ?  and does "minimum" mean that you spec 2D and buy-off 1.5D ?

RE: Aircraft edge distance

Have any of you seen or used VDI 2230?
It may be much more than you want to read
but they do have recommendations for edge
distance depending on the thickness of the
material.  I think margin by definition
would mean the material from the od of the
hole or c'sink to the edge of the material.
The spec uses edge distance and is from the
center of the hole to the edge.  I have not
seen margin used for a long time.
If edge distance is 2 times the diameter, then
margin would be 2 minus 1/2 the diameter of the
hole which would be 1.5 times the diameter.
Interesting. Are these specs a carry over from
riveting specs?

RE: Aircraft edge distance

Oops, AC65-15, not -12.  They are parts of a series of mechanic's handbooks.  Download from the Advisory Circulars page on the FAA's website.  Given their size and usefulness, I recommend getting the Jeppsen printed series.

It's of great value to know how the technician learned how to do it, and books like these are often the basis for their training (ought to be, anyway).  Like the cartoon in Bruhn asks, "Who determines the strength of a bolt?"

Steven Fahey, CET

RE: Aircraft edge distance

Something that is interesting that I found; Heritage Boeing is the only OEM that uses Edge Margin.  Everyone else seems to use Edge Distance.  Mil-HDBK-5 uses Edge Distance.  Heritage Boeing used to call Edge Margin the distance of the center of the hole to EOP if the load was normal to the EM measurement.  But somewhere it became the same as ED.  

My opinion is that Boeing should follow the rest of industry.  When I talk to Heritage Boeing I use EM but by force of habit I type ED in my repair orders and Boeing usually rejects it.

RE: Aircraft edge distance

From memory Douglas measures ED from the edge of the hole to the edge of the part where as Boeing defines it from the hole center line to the edge of the part.  The reason 1.7D edge margin is routinely considered an acceptable rework configuration is because there is no degradation from a fatigue point of view for edge margins down to 1.7D (per data in Boeing's "Book 2 - Structural Fatigue Methods and Allowables"). The degradation experienced down to 1.5D is also minimal - specially when one considers rework to an old aircraft - oops, did I say that?  surprise However, when designing repairs (or new designs) one should allow for the ocassional boo-boo - thus 2D is standard.  Also, like previously mentioned the application of load is critical to distinguish between edge margin or end margin effects regarding sheet metal. Boeing highlights differences between both in their "rework correction factors".   A short end-margin affects the fatigue quality at the lead-fastener location - NOT at the fastener suffering from a short end-margin condition - unless if tearout becomes a concern  hourglass.

RE: Aircraft edge distance

Quote from Above:
"From memory Douglas measures ED from the edge of the hole to the edge of the part."

I'm sorry to disagree with you, but Douglas has always measured E.D. from the center of the hole to the EOP. Boeing used to measure E.M. from the edge of the hole to the edge of the part. Boeing North now measures EM from the center of the hole to the EOP. Boeing South (Douglas) still measures E.D. from the center of the hole to the EOP  I have current SRM's and archieved SRM's from both companies to back this up. I wish I could post the .pdf's I sent to Boeing about this subject here for a good laugh....their responce was so typical of being caught with ones pants down..."Duh, We'll have to get back with you on that"...Quote   

RE: Aircraft edge distance

Hi whalesA3D!

Thanks for your input.  I haven't worked @ Douglas; therefore, the info I quoted was hear-say.  I appologize if inacurateupsidedown .

I worked @ Boeing from 1984-1996 mostly as a 747 Stress Analyst.  Throughout this period I am certain that Boeing's Definition of "Edge Margin" was from the center of the hole to the edge of part (Ref Boeing's D6-24957, Structural Design for Durability).  I admit thou that I have used the terms "Edge Distance" and "Edge Margin" in rather loose ways throughout my career - as long as I knew where the measurement was taken from-to 3eyes.  

Since Boeing - Everett, I have worked with Hawker de Havilland (Sydney), Civil Aviation Safety Authority - Australia, and Royal Australian Airforce and I cannot remember (again memory is a tricky beast) many instances of people measuring edge margins (or edge distances) from edge of hole to edge of part.  

You mention funny discrepancies in approach between Boeing and Douglas.  Sometimes this extends to differences between Boeing Everett (747, 767, 777) and Boeing Renton (737, 757).

RE: Aircraft edge distance

I thought it was pretty clear on the 29th Boeing defines edge margin as the center of the hole to the edge of the parts, SRM 51, period.

Everybody else in industry defines that as edge distance.  Again that's clear.

Who cares how they got there?  You just need to be cognisant of it and your QA needs to be cognisant if you are working multiple manufacturers.

Refer to the standard aircraft workers manual that has been around as long as airplanes.  Every A&P has (or should have) one Section 7 page 1.  It is different than Boeing.  However when working Boeing products SRM 51 RULES.  As does every other manufacturesr SRM 51.

Just like fasteners you have to change your terminology and callouts to be appropriate to the manufacturer.  If not you are contributing to a human factors problem.

RE: Aircraft edge distance

Wow. This is a great discussion. I really appreciate everyone's input chimming in on this one. I did not think there was this much interest. That is what is great about this forum. It sure is good to see the varied disciplines.
I do have to agree that there are a lot of factors to come up with the proper edge distance and there does not appear to be catch all for all instances. You have to work with the strength and material guys to make sure the edge distance(margin)is correct for what you are trying to accomplish.
Again I appreciate everyone's input and lively discussion.


RE: Aircraft edge distance

I have been a structures engineer for 25 years, and the biggest arguments I ever had with Design was over edge margins. I wanted the 2D + .06 margin, but Design insisted that (a) it would add too much weight, (b) Boeing never did write this down as a requirement but only as a "suggestion", and (c) Design has it's own manual that has a table of edge margin vs thickness (with values that vary from 2.2D for thin parts down to 1.44D for thick parts).

Now I am with Spirit Aerospace, and am writing the stress manual that the company will be using for future projects. You can be sure that this time 2D+.06 is going to be written down in bold print.

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