Fabric attach methods that are legal

[astjp2]

Re: Fabric attach methods that are legal

The original loading of the stamped rib using the wire is a tension load from the top of the rib. Rib lacing moved it to the bottom of the rib, that is where they get the major...

[Scott]

Re: Fabric attach methods that are legal

Hi Miguel
There is a 337 for rivets in the tech resources section. It specifies the use of 1/8" rivets but doesn't provide any information on washers, spacing or drilling new holes in the ribs. The existing holes are larger than 1/8" and of course will be damaged by the wires, so either doublers will be needed or new holes.

There is also some guidance in AC43.13-1B around page 2-57. It mentions repairs to wire and screw holes but does not provide guidance on drilling new holes. For me the holes would be the sticking point. I think you'd need to find acceptable data that supports drilling new holes but others may not think it necessary.

[Ray36048]

Re: Fabric attach methods that are legal

There is a very old STC for using screws or rivets. SA1-217 was owned by Capital Air Service. They are long gone. I checked with the FSDO several years ago and they said it was still an STC for Taylorcrafts. Someone needs to do whatever to bring this STC back with a new owner.

[Scott]

Re: Fabric attach methods that are legal

The original loading of the stamped rib using the wire is a tension load from the top of the rib. Rib lacing moved it to the bottom of the rib, that is where they get the major...

Really?
That may be a valid argument if you completely disregard the ribs have webs and are one piece, and also ignore the fact that lacing in fact transfers loads over the entire rib not just the caps/flanges.

Oh and also ignor the fact that many if not most of the holes in the ribs have by now been weekend by the wire.

Anyway, i understand the resistance to change, and fortunately we're not faced with a whole bunch of regulators forcing the fleet to go one way or another. Lots of precedence out there for alternative methods of fabric attachment going back at least 60 years, and not a single fatality linked to lacing!

Hopefully Bruce has enough information to decide on an appropriate solution for him and his certification requirements.

Sounds like the oem wire supply has or will soon run out, and even if we find or fabicate more, the problem of damaged holes remains. It would be good for all BC12D owners if thus forum could reach consensus on lacing being an excellent and proven replacement for wire.
S

[Hank Jarrett]

Re: Fabric attach methods that are legal

You are never going to get a consensus on this. Some believe it is safe, some don't. Some have seen cut lacing on stamped ribs, some haven't.
If you have seen it, you WILL NOT use lacing on stamped ribs unless the cords are protected from chaffing. Of those who have never seen it, some will think is doesn't happen, even if others have seen it.

Comes a point where those who have seen it feel like we are talking to a tree. Make your own decision and move forward.
It is NOT illegal to lace stamped ribs. Think the FAA always knows what they are talking about? I sure don't.

I have seen cut cords. I will NOT lace stamped ribs, nor will I fly in a plane that has rib stitching on stamped ribs. My opinion and worth exactly what you are paying for it. It is YOUR DECISION. Arguing is a waste of time. Read the posts and decide for yourself.

Hank

[astjp2]

Re: Fabric attach methods that are legal

You are never going to get a consensus on this. Some believe it is safe, some don't. Some have seen cut lacing on stamped ribs, some haven't.
If you have seen it, you WILL NOT use lacing on stamped ribs unless the cords are protected from chaffing. Of those who have never seen it, some will think is doesn't happen, even if others have seen it.

Comes a point where those who have seen it feel like we are talking to a tree. Make your own decision and move forward.
It is NOT illegal to lace stamped ribs. Think the FAA always knows what they are talking about? I sure don't.

I have seen cut cords. I will NOT lace stamped ribs, nor will I fly in a plane that has rib stitching on stamped ribs. My opinion and worth exactly what you are paying for it. It is YOUR DECISION. Arguing is a waste of time. Read the posts and decide for yourself.

Hank

It is not legal without approval...ie. a field approval. No need for an STC when you can still get a field approval. This is not a cessna that is still supported so the more we can do without STC's (engineering) the better off we are. Tim

[astjp2]

Re: Fabric attach methods that are legal

Really?
That may be a valid argument if you completely disregard the ribs have webs and are one piece, and also ignore the fact that lacing in fact transfers loads over the entire rib not just the caps/flanges.

Oh and also ignor the fact that many if not most of the holes in the ribs have by now been weekend by the wire.

Anyway, i understand the resistance to change, and fortunately we're not faced with a whole bunch of regulators forcing the fleet to go one way or another. Lots of precedence out there for alternative methods of fabric attachment going back at least 60 years, and not a single fatality linked to lacing!

Hopefully Bruce has enough information to decide on an appropriate solution for him and his certification requirements.

Sounds like the oem wire supply has or will soon run out, and even if we find or fabicate more, the problem of damaged holes remains. It would be good for all BC12D owners if thus forum could reach consensus on lacing being an excellent and proven replacement for wire.
S

That was PER FAA engineering....which I had to use to get a coordinated field approval. Engineers name was Dave Swartz at the Anchorage ACO. Tim

[Scott]

Re: Fabric attach methods that are legal

Fair enough Tim
Perhaps this illustrates the root of the problem i.e. regional differences in interpretation.

Wise man once told me, don't ask the question unless you already know the answer. I kinda think in this business the shortened form is don't ask the question if the regulations allow you to get the answer you want.

Anyway, as i tried to point out before, assuming factory wire is not an option, the remaining options all need the same certification decision (major or minor) so the decision on which method isn't (or shouldn't be) influenced by "legality."

[Ray36048]

Re: Fabric attach methods that are legal

Field approvals are by the regional FSDO. They are much harder to get than they were at one time. Getting a field approval can vary by FSDO. The FAA now wants STC's. STC's have the supporting engineering data the FAA wants for modifications.

[Scott]

Re: Fabric attach methods that are legal

My experience with the FAA is limited, but I sometimes find FAA documents a little less ambiguous compared to Transport Canada.

I like the decision tree FAA put together to help with the determination of whether or not your proposed alteration is major or minor. (I have parced it out here in the hopes of making it easier to follow but the whole circular is available online AC43-210A). This won't be new to many on this site but may help others in decision-making.

Note it is up to the Applicant to make the determination. (so making a reasonable determination with your AI/AP avoids the need to involve your regional FAA)


First step: "Determine if the repair/alteration is a minor change in type design (as defined in 14 CFR part 21, § 21.93); and if so, is it a major or a minor repair/alteration."

§ 21.93 Classification of changes in type design:
".. changes in type design are classified as minor and major. A “minor change” is one that has no appreciable effect on the weight, balance, structural strength, reliability, operational characteristics, or other characteristics affecting the airworthiness of the product. All other changes are “major changes” (except as provided in paragraph (b) of this section)." Note Para b is about noise and large aircraft.

Lacing is clearly a minor change to the type design, or perhaps no change at all given the type certificate A-696 applies to both stitched and non-stitched models and contains no specific reference to fabric attachment).

Next: To determine if a repair/alteration is major or minor, refer to part 43 appendix A. Figure 3-2.

(for some reason the buttons for uploading files are not working at the moment so I'll upload the file later).
First box on fig 3-2 asks: "Repair or alteration listed in products specifications?"
No
"Could the repair or alteration have an appreciable affect on:

"Weight?"
No (lacing is perhaps slightly lighter but not "appreciable")

"Balance?"
No

"Structural Strength?"
No, (fabric is not structure, no alteration to structure required)

"Performance?"
No

"Powerplant operation?"
No

"Flight characteristics?"
No

"Other qualities affecting Airworthiness?"
No, (lacing with approved materials meets applicable airworthiness standards)

"Accepted practices or elementary operations?"
Yes, (lacing was and remains an accepted practice long before the advent of alternate means of fabric attachment)

"Repair or alteration?"
Alteration.... takes us to figure 3-1 box C

"Consider as minor repair or alteration"--
"Applicant performs repair or alteration and documents in maintenance records"


I'll post the graphics when available

[Guest]

Re: Fabric attach methods that are legal

I wouldn't use part 21 to determine what a mechanic can do.

Part 21 is for making changes to the type design, that's for manufactures, TC holders, STC determination and so on.

U.S. mechanics operate under part 43 and 65 mostly. I would use part 43 appendix A and part 1 definitions.

Probably you get to the same endpoint Scott but part 21 is about design changes whereas we mechanics do not make design changes we modify one instance (serial number) of the design unless we happen to be making an STC or considering that.

Dave R

[Scott]

Re: Fabric attach methods that are legal

I Understand
I was following the process outlined in the AC which deals with both. I guess they want you first to establish that the proposed alteration is not significant enough to require a change in Type Design, then it moves on to the Part 43 stuff. Everything in my post from "Fig 3-2" on is part 43.
when I get posting tools and upload capability back I'll try again

[Guest]

Re: Fabric attach methods that are legal

For me part 21 is helping decide is a type certificate holder or an interested party is making a change that is significant enough to require change to the type certificate or perhaps a supplement to it.

The "major-ness" of that is important as you point out. One could decide that the change has sufficient "major-ness" under part 21 and determine that it is a major alteration. But... by sticking to part 43 and part 1 you get to do anything listed in the TCDS specification list items (I think I said the right) as an alteration (a.k.a minor).

Seems like a dopey explanation but can save you uneeded paperwork.

https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/?year=all&q=rude&bSubmit=Search

Dave R

[Garry Crookham]

I'm deep into a major hangar cleanup and came across an envelope containing a couple of pages concerning Martin fabric clips and a template for drilling a series of new holes:

[Bruce Caldwell]

I sure appreciate all of your help! Still not sure what to do though. I can't find the 337 in the tech section but I haven't gone through all 15 pages. Thanks again!
Bruce