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PVC Conduit in Certificated Aircraft

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jluckey(at)pacbell.net
Guest

Posted: Sat Sep 30, 2023 8:58 am Post subject: PVC Conduit in Certificated Aircraft

Does anyone know if PVC can be used for a wiring conduit in Certificated aircraft?

It is my understanding that the reason we use Tefzel wire in aircraft is to minimize the toxic gasses given-off from burning insulation.  The more common (and cheaper) automotive-type wire is a no-no because its insulation is PVC-based and its fumes are very toxic.

So I was surprised to hear an A&P suggest a PVC conduit in a Certified airframe.  



TIA





-Jeff

email(at)jaredyates.com
Guest

Posted: Sat Sep 30, 2023 9:08 am Post subject: PVC Conduit in Certificated Aircraft

I'd say the answer to your question depends on the IA who is going to be signing off the Annual, but may I propose that if you're going to shop in the plumbing department, I like Pex better than PVC.



On Sat, Sep 30, 2023 at 1:03â€¯PM Jeff Luckey <jluckey(at)pacbell.net (jluckey(at)pacbell.net)> wrote:



 	  Quote: 	
		  Does anyone know if PVC can be used for a wiring conduit in Certificated aircraft?

It is my understanding that the reason we use Tefzel wire in aircraft is to minimize the toxic gasses given-off from burning insulation.Â  The more common (and cheaper) automotive-type wire is a no-no because its insulation is PVC-based and its fumes are very toxic.

So I was surprised to hear an A&P suggest a PVC conduit in a Certified airframe.Â  



TIA





-Jeff

Ceengland

Joined: 11 Oct 2020
Posts: 381
Location: MS

Posted: Sat Sep 30, 2023 1:09 pm Post subject: PVC Conduit in Certificated Aircraft

On 9/30/2023 11:57 AM, Jeff Luckey       wrote:

     

      	  Quote: 	
		                         Does anyone know if PVC can           be used for a wiring conduit in Certificated aircraft?

         

         

         It is my understanding that           the reason we use Tefzel wire in aircraft is to minimize the           toxic gasses given-off from burning insulation.Â  The more           common (and cheaper) automotive-type wire is a no-no because           its insulation is PVC-based and its fumes are very toxic.

         

         

         So I was surprised to hear an           A&P suggest a PVC conduit in a Certified airframe.Â  

         

         

         

         

         

         TIA

         

         

         

         

         -Jeff

         

         

         

       

     	
     PVC has a much lower temperature rating than Tefzel. IIRC, it's also     a bit more vulnerable to moisture migration through it to the     copper. I believe that all the insulations, including Tefzel, emit     nasty gases when they burn.

   Virus-free.www.avast.com[url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]

_________________
Charlie

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Sep 30, 2023 5:32 pm Post subject: PVC Conduit in Certificated Aircraft

At 11:57 AM 9/30/2023, you wrote:

  	  Quote: 	
		  Does anyone know if PVC can be used for a wiring conduit in Certificated aircraft? 	


   A TC aircraft left the factory configured

   per approved drawings. Substituting any

   part not on that drawing requires an

   approval via one-time field approval (Form 337)

   or an STC.



   I can't imagine any licensed technician

   attempting to 'sell' such a deviation

   to the local FSDO.



   What kind of 'mod' are we talking about?

   If the wires were not part of the original

   TC then one is advised to rely on 

   legacy practices when submitting a Form 337.

   To be sure, PVC plumbing would not fall in that category.

  



 

 

   Bob . . .



                    //// 

                   (o o) 

    ===========o00o=(_)=o00o========= 

    < Go ahead, make my day . . .   > 

    < show me where I'm wrong.      > 

    =================================

  

    In the interest of creative evolution

    of the-best-we-know-how-to-do based

    on physics and good practice.

jluckey(at)pacbell.net
Guest

Posted: Sun Oct 01, 2023 8:37 am Post subject: PVC Conduit in Certificated Aircraft

Bob and others,

I want to summarize ...

Bob - I understand, agree with, and appreciate your cogent and concise explanation of the rules.  Right on the money, as usual.



However, as far as anyone who responded knows, there is no FAR or other regulation that would prohibit the use of a PVC conduit in a Certificated airframe. 



If an A&P/IA completes a 337 and gets it approved by their local FSDO, a piece of PVC could be used in a Certificated airplane.  It is really up to the FSDO and the relationship that A&P has with them.  I understand that the approval process might be challenging, but there is no reg that prohibits the use of PVC as a conduit.

Over the past few years, I have come to discover that what is dis-allowed by one FSDO might be approved by another.  I was surprised to find out just how capricious and inconsistent the application of the rules is from district to district across the country. 





For the record, I am not considering using PVC for a conduit in a Certificated or Experimental aircraft.  Based on my understanding of the toxic properties of PVC, I would not consider it.  I had overheard a conversation with an IA who suggested using a piece of PVC in the tail of an Experimental and he went on to say that "he had done it in a Cessna".  And I thought that was odd and I also thought: "I wouldn't let this guy work on MY airplane".



-Jeff



                  

                                                                    On Saturday, September 30, 2023 at 06:37:37 PM PDT, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:                 

                 



                 



                   At 11:57 AM 9/30/2023, you wrote:

  	  Quote: 	
		  Does anyone know if PVC can be used for a wiring conduit in Certificated aircraft? 	


   A TC aircraft left the factory configured

   per approved drawings. Substituting any

   part not on that drawing requires an

   approval via one-time field approval (Form 337)

   or an STC.



   I can't imagine any licensed technician

   attempting to 'sell' such a deviation

   to the local FSDO.



   What kind of 'mod' are we talking about?

   If the wires were not part of the original

   TC then one is advised to rely on 

   legacy practices when submitting a Form 337.

   To be sure, PVC plumbing would not fall in that category.

  



 

 

    Bob . . .



                    //// 

                   (o o) 

    ===========o00o=(_)=o00o========= 

    < Go ahead, make my day . . .   > 

    < show me where I'm wrong.      > 

    =================================

  

    In the interest of creative evolution

    of the-best-we-know-how-to-do based

    on physics and good practice.

alec(at)alecmyers.com
Guest

Posted: Mon Oct 02, 2023 6:26 pm Post subject: PVC Conduit in Certificated Aircraft

I have a small certified aircraft with PVC tubes. I just read the 3000 hour inspection checklist that requires them to be inspected. Thereâ€™s a cable conduit under the cabin floor that Iâ€™m pretty sure is PVC, although Iâ€™m not sure if thatâ€™s one that needs inspecting. Some of the control surfaces have PVC tubes in.



Searching through the maintenance manual, I see that the entire structure of the aircraft is described variously as "GRP skins [AND] a rigid PVC foam coreâ€, and thereâ€™s a lot of rigid PVC foam too.

On Oct 1, 2023, at 12:37, Jeff Luckey <jluckey(at)pacbell.net> wrote:



Bob and others,



I want to summarize ...



Bob - I understand, agree with, and appreciate your cogent and concise explanation of the rules.  Right on the money, as usual.



However, as far as anyone who responded knows, there is no FAR or other regulation that would prohibit the use of a PVC conduit in a Certificated airframe. 



If an A&P/IA completes a 337 and gets it approved by their local FSDO, a piece of PVC could be used in a Certificated airplane.  It is really up to the FSDO and the relationship that A&P has with them.  I understand that the approval process might be challenging, but there is no reg that prohibits the use of PVC as a conduit.



Over the past few years, I have come to discover that what is dis-allowed by one FSDO might be approved by another.  I was surprised to find out just how capricious and inconsistent the application of the rules is from district to district across the country. 

For the record, I am not considering using PVC for a conduit in a Certificated or Experimental aircraft.  Based on my understanding of the toxic properties of PVC, I would not consider it.  I had overheard a conversation with an IA who suggested using a piece of PVC in the tail of an Experimental and he went on to say that "he had done it in a Cessna".  And I thought that was odd and I also thought: "I wouldn't let this guy work on MY airplane".



-Jeff



On Saturday, September 30, 2023 at 06:37:37 PM PDT, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote: 

At 11:57 AM 9/30/2023, you wrote:

 	  Quote: 	
		   Does anyone know if PVC can be used for a wiring conduit in Certificated aircraft?


	


  A TC aircraft left the factory configured

  per approved drawings. Substituting any

  part not on that drawing requires an

  approval via one-time field approval (Form 337)

  or an STC.



  I can't imagine any licensed technician

  attempting to 'sell' such a deviation

  to the local FSDO.



  What kind of 'mod' are we talking about?

  If the wires were not part of the original

  TC then one is advised to rely on 

  legacy practices when submitting a Form 337.

  To be sure, PVC plumbing would not fall in that category.

 

  Bob . . .



                   //// 

                  (o o) 

   ===========o00o=(_)=o00o========= 

   < Go ahead, make my day . . .   > 

   < show me where I'm wrong.      > 

   =================================

 

   In the interest of creative evolution

   of the-best-we-know-how-to-do based

   on physics and good practice.

alec(at)alecmyers.com
Guest

Posted: Mon Oct 02, 2023 6:28 pm Post subject: PVC Conduit in Certificated Aircraft

Sorry - that should say â€œa lot of rigid PVC honeycomb tooâ€.

On Oct 2, 2023, at 22:25, Alec Myers <alec(at)alecmyers.com> wrote:






I have a small certified aircraft with PVC tubes. I just read the 3000 hour inspection checklist that requires them to be inspected. Thereâ€™s a cable conduit under the cabin floor that Iâ€™m pretty sure is PVC, although Iâ€™m not sure if thatâ€™s one that needs inspecting. Some of the control surfaces have PVC tubes in.



Searching through the maintenance manual, I see that the entire structure of the aircraft is described variously as "GRP skins [AND] a rigid PVC foam coreâ€, and thereâ€™s a lot of rigid PVC foam too.

On Oct 1, 2023, at 12:37, Jeff Luckey <jluckey(at)pacbell.net> wrote:



Bob and others,



I want to summarize ...



Bob - I understand, agree with, and appreciate your cogent and concise explanation of the rules.  Right on the money, as usual.



However, as far as anyone who responded knows, there is no FAR or other regulation that would prohibit the use of a PVC conduit in a Certificated airframe. 



If an A&P/IA completes a 337 and gets it approved by their local FSDO, a piece of PVC could be used in a Certificated airplane.  It is really up to the FSDO and the relationship that A&P has with them.  I understand that the approval process might be challenging, but there is no reg that prohibits the use of PVC as a conduit.



Over the past few years, I have come to discover that what is dis-allowed by one FSDO might be approved by another.  I was surprised to find out just how capricious and inconsistent the application of the rules is from district to district across the country. 

For the record, I am not considering using PVC for a conduit in a Certificated or Experimental aircraft.  Based on my understanding of the toxic properties of PVC, I would not consider it.  I had overheard a conversation with an IA who suggested using a piece of PVC in the tail of an Experimental and he went on to say that "he had done it in a Cessna".  And I thought that was odd and I also thought: "I wouldn't let this guy work on MY airplane".



-Jeff



On Saturday, September 30, 2023 at 06:37:37 PM PDT, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote: 

At 11:57 AM 9/30/2023, you wrote:

 	  Quote: 	
		   Does anyone know if PVC can be used for a wiring conduit in Certificated aircraft?


	


 A TC aircraft left the factory configured

 per approved drawings. Substituting any

 part not on that drawing requires an

 approval via one-time field approval (Form 337)

 or an STC.



 I can't imagine any licensed technician

 attempting to 'sell' such a deviation

 to the local FSDO.



 What kind of 'mod' are we talking about?

 If the wires were not part of the original

 TC then one is advised to rely on 

 legacy practices when submitting a Form 337.

 To be sure, PVC plumbing would not fall in that category.



 Bob . . .



                  //// 

                 (o o) 

  ===========o00o=(_)=o00o========= 

  < Go ahead, make my day . . .   > 

  < show me where I'm wrong.      > 

  =================================



  In the interest of creative evolution

  of the-best-we-know-how-to-do based

  on physics and good practice.

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Oct 02, 2023 9:34 pm Post subject: PVC Conduit in Certificated Aircraft

 	  Quote: 	
		  Bob and others,



 I want to summarize ...



 Bob - I understand, agree with, and appreciate your cogent and concise explanation of the rules.  Right on the money, as usual.



 However, as far as anyone who responded knows, there is no FAR or other regulation that would prohibit the use of a PVC conduit in a Certificated airframe. 	


    Didn't say there was . . . only that deviations

    from the airplane's type certification is

    to be discouraged without overriding approval

    lest lightning from on high come down and smite thee.



    Now, if some manufacture has achieved certification

    with ANY particular material, then that TC

    becomes "approved data" but only for that particular

    application. PVC approved in one place doesn't say

    okay to use anywhere.



  	  Quote: 	
		  If an A&P/IA completes a 337 and gets it approved by their

 local FSDO, a piece of PVC could be used in a Certificated

 airplane.  It is really up to the FSDO and the relationship

 that A&P has with them.  I understand that the approval

 process might be challenging, but there is no reg that

 prohibits the use of PVC as a conduit. 	


   I recall rules that speak to flammability of any

   material used on the airframe. The topic got really

   hot after Swissair 111 suffered some soft fault ignition

   of insulation in the overhead. Something about

   flaming drips, self extinguishing times, fumes, proximity

   to critical systems, etc.



   Yup, here 'tis:  

   

    https://www.faa.gov/documentlibrary/media/advisory_circular/ac%2023-2a.pdf

 

 



  	  Quote: 	
		  Over the past few years, I have come to discover that what is

 dis-allowed by one FSDO might be approved by another.  I

 was surprised to find out just how capricious and inconsistent

 the application of the rules is from district to district across the country. 	


   You got that right! In years past seekers of royal

   permission would FSDO Shop . . . Back then Ft. Worth

   and Seattle were popular shops. Last I heard, 

   the practice was halted with a directive, "Tho

   shalt seek blessings only from thy local FSDO."



   I think the Teterboro office got miffed 'cause

   nobody ever asked them for permission/guidance . . .

   wonder why.



  	  Quote: 	
		  I had overheard a conversation with an IA who suggested using a

 piece of PVC in the tail of an Experimental and he went on to

 say that "he had done it in a Cessna".  And I thought

 that was odd and I also thought: "I wouldn't let this guy work on MY airplane". 	


   I wonder if he jumped the hoops for paperwork.

   There's nothing inherently hazardous for incorporation

   of PVC . . . depends on application and exacerbation

   of risk. But the absolutely minimal risk solutions

   call for consideration of better materials

   first. I suspect PVC conduit in the tailcone is not

   a significant elevation of risk.



 

   Bob . . .



                    //// 

                   (o o) 

    ===========o00o=(_)=o00o========= 

    < Go ahead, make my day . . .   > 

    < show me where I'm wrong.      > 

    =================================

  

    In the interest of creative evolution

    of the-best-we-know-how-to-do based

    on physics and good practice.

N38CW

Joined: 16 Apr 2008
Posts: 57
Location: Winston-Salem, NC

Posted: Tue Oct 03, 2023 12:42 am Post subject: PVC Conduit in Certificated Aircraft

What is the aircraft?



Thanks,

Bill



--

_________________
Bill Settle
RV-8 Fuselage

alec(at)alecmyers.com
Guest

Posted: Tue Oct 03, 2023 2:35 am Post subject: PVC Conduit in Certificated Aircraft

Bob,



That link is to a document describing flammability tests. It doesnâ€™t have any advice as to where flammable (or other) materials can be used.

There is in it a list of regulatory references (on page 7) that apply to individual parts of the aircraft, but they are very very specific. It may have been extended since 2007 when that AC was issued.



Looking through the FAR sections listed there that appear to apply to cables and accessories, the only relevant stipulation is this one:



23.1365(b) Any equipment that is associated with any electrical cable installation and that would overheat in the event of circuit overload or fault must be flame resistant. That equipment and the electrical cables must not emit dangerous quantities of toxic fumes.

If a circuit is protected, does it still count as something that would overheat in the event of overload or fault?



 





On Oct 3, 2023, at 01:34, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:



 	  Quote: 	
		   Bob and others,

 

 I want to summarize ...

 

 Bob - I understand, agree with, and appreciate your cogent and concise explanation of the rules.  Right on the money, as usual.

 

 However, as far as anyone who responded knows, there is no FAR or other regulation that would prohibit the use of a PVC conduit in a Certificated airframe.


	


   Didn't say there was . . . only that deviations

   from the airplane's type certification is

   to be discouraged without overriding approval

   lest lightning from on high come down and smite thee.



   Now, if some manufacture has achieved certification

   with ANY particular material, then that TC

   becomes "approved data" but only for that particular

   application. PVC approved in one place doesn't say

   okay to use anywhere.



 	  Quote: 	
		   If an A&P/IA completes a 337 and gets it approved by their

 local FSDO, a piece of PVC could be used in a Certificated

 airplane.  It is really up to the FSDO and the relationship

 that A&P has with them.  I understand that the approval

 process might be challenging, but there is no reg that

 prohibits the use of PVC as a conduit.


	


  I recall rules that speak to flammability of any

  material used on the airframe. The topic got really

  hot after Swissair 111 suffered some soft fault ignition

  of insulation in the overhead. Something about

  flaming drips, self extinguishing times, fumes, proximity

  to critical systems, etc.



  Yup, here 'tis:  

  

  https://www.faa.gov/documentlibrary/media/advisory_circular/ac%2023-2a.pdf

alec(at)alecmyers.com
Guest

Posted: Tue Oct 03, 2023 2:39 am Post subject: PVC Conduit in Certificated Aircraft

Itâ€™s a Grob G115



On Oct 3, 2023, at 04:41, Bill Settle <billsettle(at)bellsouth.net> wrote:






What is the aircraft?



Thanks,

Bill



--

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Oct 03, 2023 6:04 pm Post subject: PVC Conduit in Certificated Aircraft

 	  Quote: 	
		  

 Looking through the FAR sections listed there that appear to apply to cables and accessories, the only relevant stipulation is this one:



 23.1365(b) Any equipment that is associated with any electrical cable installation and that would overheat in the event of circuit overload or fault must be flame resistant. That equipment and the electrical cables must not emit dangerous quantities of toxic fumes.



 

 If a circuit is protected, does it still count as something that would overheat in the event of overload or fault? 	


   One would think. I've heard opinions from more than

   one 'knowing' source. One agreed with that assertion.

   The other did not . . . everything on the 

   ship's TC was originally assessed for fire risks.

   Anything new is subject to the same assessment.



 

   Bob . . .



                    //// 

                   (o o) 

    ===========o00o=(_)=o00o========= 

    < Go ahead, make my day . . .   > 

    < show me where I'm wrong.      > 

    =================================

  

    In the interest of creative evolution

    of the-best-we-know-how-to-do based

    on physics and good practice.

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