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Thread: Approval for welded-in shoulder harness tabs

  1. #1
    dave's Avatar
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    Approval for welded-in shoulder harness tabs

    AC-23-4 states "The FAA does not encourage the approval of retrofit shoulder harness installations as minor changes. The preferred methods of approval are Supplemental Type Certificate or Field Approval. However, the FAA should notforbid the approval of a retrofit shoulder harness installation as a minor change in the front seats of those small airplanes manufactured before July 19, 1978, and in other seats of those small airplanes manufactured before December 13, 1986. A retrofit shoulder harness installation may receive approval as a minor change in these small airplanes if: The installation requires no change of the structure (such as welding or drilling holes).

    My question, does anybody know of a way to weld in Atlee Dodge shoulder harness tabs as a minor alteration?
    Last edited by dave; 08-02-2012 at 04:01 PM.
    Physics always bats last.

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    Look at AC 43.13-2B, chapter 9. If your mechanic has any question whether the modification is minor or major have him review the opening chapter of the AC regarding use of the AC as approved data for major alterations.

    http://www.faa.gov/documentLibrary/m...2043.13-2B.pdf

    SB
    Last edited by sierra bravo; 08-02-2012 at 02:12 PM.

  3. #3
    dave's Avatar
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    Thanks SB, As I read it welding the tabs becomes a major alteration. I'm sending it on for others to evaluate. DK
    Physics always bats last.

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    I think the interpretation is subjective. For instance...
    a. Minor alterations are limited to those where no change in the aircraft structure is required for
    mounting the harness. If the installation does not
    require operations such as drilling holes into or
    welding brackets onto the primary structure, it could
    be classified as a minor alteration. (See Figure 9-1.)
    Two examples of minor alterations for shoulder
    harnesses are:
    Is the tab attaching to "primary" structure? If it isn't primary structure, the limitation isn't applicable, right?

    In any event, a major alteration with approved data can be signed off by an IA without involving the FAA. The AC gives you the data he needs to do it.

  5. #5
    dave's Avatar
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    We have one engineer's opinion that it does attach to a primary structure.

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    Physics always bats last.

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    Quote Originally Posted by dave View Post
    We have one engineer's opinion that it does attach to a primary structure.

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    Looks to me like you added a base for the standoff at the skylight. Nice touch using the standoff base for the harness attach point.

    Seriously, I understand the general concern about adding a welded tab on a tube. In this case, if there's enough force on the attach tab to do damage to the tube? You probably have bigger problems to worry about. It's a little silly that you can attach the harness anchor to the tube with a cable choker or a tube clamp but not a welded tab. The engineer needs a dose of common sense.
    Last edited by sierra bravo; 08-02-2012 at 06:01 PM.

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    S2D's Avatar
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    Quote Originally Posted by sierra bravo View Post
    In any event, a major alteration with approved data can be signed off by an IA without involving the FAA. The AC gives you the data he needs to do it.
    When did AC43.13-2B become "approved" data? I always thought it was "acceptable" data? Big difference!!
    I may be wrong but that probably won't stop me from arguing about it.
    Likes Charlie Longley liked this post

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    Brian,

    Read the opening paragraph of AC 43.13-2B.

    SB

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    S2D's Avatar
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    Yes I was just trying to beat you to delete.!!!!
    This data generally pertains to minor alterations; however, the alteration data herein may be used as approved data for major alterations when the AC chapter, page, and paragraph are listed in block 8 of FAA Form 337 when the user has determined that it is:
    a.
    Appropriate to the product being altered,
    b.
    Directly applicable to the alteration being made, and
    c.
    Not contrary to manufacturer’s data.


    Refer to this

    (4) Manufacturer Data. Some manufacturers have developed service kits or service instructions that are FAA-approved for harness retrofit installations. Some manufacturers have developed service kits or service instructions that are FAA-approved for harness retrofit installations. Depending on the complexity, these installations may be performed as major or minor alterations. For example, if the installation consists of affixing harness assemblies to existing hard points such as nutplates, the installation could be classified as minor, with no requirement to complete FAA Form 337. If the kit is FAA-approved but results in modification to the airframe structure, FAA Form 337 must be completed, referencing the approved kit/instructions, with no additional approval required.
    (5) Other FAA-Approved Data
    Last edited by S2D; 08-02-2012 at 06:26 PM.
    I may be wrong but that probably won't stop me from arguing about it.

  11. #11
    S2D's Avatar
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    If they are doing it without a kit, per the AC, they still need approval.
    I may be wrong but that probably won't stop me from arguing about it.

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    If they comply with the AC instructions they do not need further approval. Dave's problem is that the tab in the photo isn't attached adjacent to a tube intersection. The AC doesn't prohibit the tab's attachment elsewhere in the tube, it simply says attachment "should" be near a tube intersection. Should? Near? Pretty subjective. That interpretation thing again. The AC clearly defines a welded tab as a major alteration but with the approved data provided in the AC the 337 can be filed without approval. Frankly I can't believe a DER wouldn't sign it off. The intent is to protect the pilot.

  13. #13
    S2D's Avatar
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    Stewart,
    Para 903 b. lists the methods to accomplish the major alteration.
    Where are you finding other info for accomplishing a major alteration for installing a shoulder harness?
    Brian
    I may be wrong but that probably won't stop me from arguing about it.

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    Part 5 of the paragraph that you referenced. The AC document itself is approved data when properly referenced on the 337.

  15. #15
    S2D's Avatar
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    Yea.
    Not as simple as just entering in logbook, "installed I/A/W 43.13-2B Chapter X para Y."
    Brian

    ( I might have one of these in my shed needing certified when I get done with all the paperwork. Just as well see how they get theirs done first]
    I may be wrong but that probably won't stop me from arguing about it.

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    Darrel Starr's Avatar
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    During the rebuild of our SC, I called Atlee to enquire about his bolt-on shoulder harness fitting. He said, "Isn't this plane all apart with no cover?" I said "Yes". Then a little agitated, he said " Well then just weld the #$%!@ bracket on, don't bother with the bolted on one" So we did and my IA had no qualms about signing it off as a minor mod.

  17. #17
    S2D's Avatar
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    Does the FADodge kit have any paperwork for it?

    If the kit is FAA-approved but results in modification to the airframe structure, FAA Form 337 must be completed, referencing the approved kit/instructions, with no additional approval required.

    Does anyone have a letter from the FAA saying a welded on tab is ok as a minor repair
    I may be wrong but that probably won't stop me from arguing about it.

  18. #18
    spinner2's Avatar
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    Quote Originally Posted by Darrel Starr View Post
    During the rebuild of our SC, I called Atlee to enquire about his bolt-on shoulder harness fitting. He said, "Isn't this plane all apart with no cover?" I said "Yes". Then a little agitated, he said " Well then just weld the #$%!@ bracket on, don't bother with the bolted on one" So we did and my IA had no qualms about signing it off as a minor mod.
    Steve Kracke made an almost identical statement to me about a rear shoulder harness bracket. My IA had no problem with it being welded either.


    Sent from my iPhone from the middle of nowhere using Tapatalk
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  19. #19
    Darrel Starr's Avatar
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    All the SCs around here have welded in shoulder harness brackets. Some of us have been ramp checked without anyone commenting about the brackets.

  20. #20
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by sierra bravo View Post
    If they comply with the AC instructions they do not need further approval. Dave's problem is that the tab in the photo isn't attached adjacent to a tube intersection. The AC doesn't prohibit the tab's attachment elsewhere in the tube, it simply says attachment "should" be near a tube intersection. Should? Near? Pretty subjective. That interpretation thing again. The AC clearly defines a welded tab as a major alteration but with the approved data provided in the AC the 337 can be filed without approval. Frankly I can't believe a DER wouldn't sign it off. The intent is to protect the pilot.

    correct.. fill out 337, send it to Oak.....

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    I would guess that most people reading this, if they have ever bent a SC, will think that shoulder harness are a good thing. I also think that most will agree that it is perfectly legal to wrap the shoulder harness tiedown around the cross member or use bolt-on attachment
    (see http://rgl.faa.gov/Regulatory_and_Gu...LE/AC21-34.pdf, so if the foregoing is correct, just welding a tab is a major alteration??? This is called not being able to seperate the forest from the trees. Maybe the IA has his head up his ---.

  22. #22
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by djfraudman View Post
    I would guess that most people reading this, if they have ever bent a SC, will think that shoulder harness are a good thing. I also think that most will agree that it is perfectly legal to wrap the shoulder harness tiedown around the cross member or use bolt-on attachment
    (see http://rgl.faa.gov/Regulatory_and_Gu...LE/AC21-34.pdf, so if the foregoing is correct, just welding a tab is a major alteration??? This is called not being able to seperate the forest from the trees. Maybe the IA has his head up his ---.

    welding makes it major... thats all.... not what you weld... no biggie..

  23. #23
    S2D's Avatar
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    The issue is not what everybody has done and got away with it, but what the regs and A/C's actually say. The aircraft in question is being built for sale, possibly to the head of the FSDO somewhere. Want to sign your name to something that isn't exactly correct.
    I may be wrong but that probably won't stop me from arguing about it.

  24. #24
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by S2D View Post
    The issue is not what everybody has done and got away with it, but what the regs and A/C's actually say. The aircraft in question is being built for sale, possibly to the head of the FSDO somewhere. Want to sign your name to something that isn't exactly correct.
    most things are not EXACTLY correct , I base my statement on my FSDO guy's answer to that question..... (and ONCE you get a RIGHT answer NEVER ask the question AGAIN!!)

    He also thought that 43 2b being good data was a mistake on FAA's part.....

  25. #25

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    There's a simple answer, cut the tab off and bolt on a holder or wrap the shoulder harness around the cross-tube.
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  26. #26
    dave's Avatar
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    Quote Originally Posted by S2D View Post
    The issue is not what everybody has done and got away with it, but what the regs and A/C's actually say. The aircraft in question is being built for sale, possibly to the head of the FSDO somewhere. Want to sign your name to something that isn't exactly correct.
    Hey Brian, You are correct. We wouldn't ask Jeff to do anything he is uncomfortable with. I spoke with the Helena FSDO this afternoon and it looks like we can support a 337 based on the criteria described by Brian and SB. My hope is that we can make this process easier for the next guy.
    Physics always bats last.

  27. #27
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by S2D View Post
    When did AC43.13-2B become "approved" data? I always thought it was "acceptable" data? Big difference!!
    last update....

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    Steve Pierce's Avatar
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    Quote Originally Posted by dave View Post
    Hey Brian, You are correct. We wouldn't ask Jeff to do anything he is uncomfortable with. I spoke with the Helena FSDO this afternoon and it looks like we can support a 337 based on the criteria described by Brian and SB. My hope is that we can make this process easier for the next guy.
    That is great Dave. Thanks for spending the time and sharing this with the rest of us. It will definitely help.
    Steve Pierce

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  29. #29
    S2D's Avatar
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    If one wanted to do a stress test per Para 5 on a mock up what would be the pounds to test to?
    I may be wrong but that probably won't stop me from arguing about it.

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    For the shoulder restraint? Part 924 of the AC defines load and distribution. The prescribed value for the section for the normal category is a 170# occupant and a distribution of 60% of the load to the lap belt, 40% to the shoulder harness. Table 9-1 shows a pre-1969 type certificated airplane static test requirement at 704# in the forward direction.

    Again, it's interesting that the determining factors are a 9g load applied statically for 3 seconds without causing permanent damage to the structure. If I endure a 9g load in an airplane for 3 seconds I'm having a bad day. Repairing the harness attach structure would be the least of my problems.

    One of the structural engineer types on the site should be able to calculate the defection and failure of a 4130 tube of a defined length with a 704# load. That engineering should be adequate for the purposes of the AC requirements, shouldn't it? Or lacking that, a similar tube should be able to be tested with a welded tab in simulated conditions (same tube specs, same tube span) outside the airplane.
    Last edited by sierra bravo; 08-03-2012 at 11:18 AM.

  31. #31
    aviationinfo's Avatar
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    Not being an A&P I'm reading the above esoteric discussion and thinking--- is it better to have a freaking shoulder harness or is it not??? Just saying. I thought that was the FAA's opinion too and they were supposed to be making it easier to install one. Sorry for the thread creep.

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    Aviator's Avatar
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    This topic has been debated before. I think highly of Atlee Dodge's work, but I suspect they didn't complete the load analysis in this case. I'm no structures man, but as rule, ANY load applied perpendicular to a beamcolumn is excessive.

    "Carrythrough tubes, highly loaded in compression, may experience a beamcolumn buckling failure if the occupant applies a load to the shoulder harness attachment. In some cases, very small loads on the shoulder harness attachment may cause beam-column buckling failures." Policy Statement Number ACE-00-23.561-01, Issuance of Policy Statement, Methods of Approval of Retrofit Shoulder Harness http://www.faa.gov/aircraft/gen_av/h...lderpolicy.pdf

  33. #33
    Steve Pierce's Avatar
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    After that beam load is applied to the rear carry-thru I suspect any damage to it is the least of your worries. This is how Univair does it.
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    From this http://www.pierceaero.net/techdata/rsh.pdf it looks like the FAA thinks something is better than nothing. Also, there are STC's to clamp to this, just none to weld.
    Steve Pierce

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  34. #34
    Aviator's Avatar
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    If I read the Policy Statement correctly, their concern is in-flight failure of the carry-through caused by the load. Great pic, though, thanks.

    I admit the front harness setup design on my -18A is by no means an award winner - actually, it's kind of crappy - but it seems to do the job and it's legal. I don't really like the cross-strap that ties the two shoulder straps together (it's something to get tangled up in), but it does give some lateral protection (the stitching was done in an approved shop). It's adjustable from just behind the head all the way up to about 8" from the carry-through (the higher up the greater the load on the stitches). I set it to about 16" fwd so it limits any head rebound, too. An alternative would be a single diagonal, but those things don't impress me.

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    Back seat shoulder straps anchor

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    Front seat shoulder straps anchors

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    Comments would be appreciated. Thanks.
    Last edited by Aviator; 08-10-2012 at 10:55 AM.

  35. #35
    Steve Pierce's Avatar
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    Nice install. I want to pursue an STC for the weld in shoulder harness attach fittings. I have gotten access to the structural test data and have a call into my FSDO for a contact at the ACO to send my packet to. I think this is a much need modification.
    Steve Pierce

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  36. #36
    cubunltd's Avatar
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    I've never had the local FSDO turn down a 337 for a welded on shoulder harness bracket. I must be lucky to have a FSDO with some common sense.

    John

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    I’ve read through this, and as a mostly non-mechanical type am thoroughly flummoxed. I do not have to my knowledge any logbook entry, and definitely no 337 for my shoulder harnesses in my new -12. Any thoughts on this setup?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    HAVE FUN. DON'T DIE.

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    Ya, my input is that setup is as useful as tits on a boar hog!!! Just saying.
    DENNY
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  39. #39
    skywagon8a's Avatar
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    Quote Originally Posted by Kodiakmack View Post
    I’ve read through this, and as a mostly non-mechanical type am thoroughly flummoxed. I do not have to my knowledge any logbook entry, and definitely no 337 for my shoulder harnesses in my new -12. Any thoughts on this setup?


    Upon impact that piece of string will break and you will smash your face into the instrument panel. The harness should be threaded through that small triangle behind the X joint. That's what the short cross piece of tubing is there for, to hold the harness at the correct angle.
    N1PA
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  40. #40
    Steve Pierce's Avatar
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    Quote Originally Posted by Kodiakmack View Post
    I’ve read through this, and as a mostly non-mechanical type am thoroughly flummoxed. I do not have to my knowledge any logbook entry, and definitely no 337 for my shoulder harnesses in my new -12. Any thoughts on this setup?
    Make a log book entry referencing the FAA Policy Statement.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
    Likes mike mcs repair liked this post

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