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FAR 21.9 provides the ability to install parts that were "Produced by an owner or operator for maintaining or altering that owner or operator's product". This seems like a pretty broad scope of authority for aircraft owners.

Under what circumstances are owner-produced parts typically used, and what requirements are imposed on the part (and the owner producing it)?

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    $\begingroup$ What kind of part? A 3D-printed plastic seat belt holder for your Cessna will receive one level of inspection, a hand-forged fan blade for a Trent 970 will receive a bit more scrutiny. $\endgroup$ – paul Aug 31 '14 at 23:49
  • $\begingroup$ and a piece of duct tape to cover the hole in the wing of your Cessna, hmmm. (and yes, I've seen that, had I known more about aircraft maintenance requirements at the time I'd not have climbed on board that thing...). $\endgroup$ – jwenting Sep 1 '14 at 14:37
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    $\begingroup$ Wasn't duct tape. There is an FAA-approved product called speed tape that looks almost identical ( 2 inches wide, silver ) and is commonly used for temporary repairs. If you've never seen the proper stuff up close you won't know the difference. $\endgroup$ – paul Sep 1 '14 at 21:28
  • $\begingroup$ @paul if there's a difference describe it in your answer. (As far as I'm aware there isn't: you have to demonstrate equivalence in either case...) $\endgroup$ – voretaq7 Sep 2 '14 at 1:49
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    $\begingroup$ A while back I needed to replace a flap track on my old Cessna 340. The company that produced them was still in business, but did not have the part. I had them produced the part according to their specs. I received a traveler (the little white card) for it, that said the item was produced at the owner's direction referencing the FAR above and their STC. My A&P replaced the existing track with the new part and made an entry in the log book stating that they replaced the old track with a new track manufactured per the FAR. I had a FAA review of the logs at a later date with no issues. $\endgroup$ – JerryKur Sep 8 '14 at 22:54
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The July/August 2002 edition of FAAviation News (now FAA Safety Briefing) has a detailed article on owner-produced parts, including advice on best practices if you want to make your own parts. It does confirm that owners have very broad authority to do so, provided that they document everything properly.

Typical reasons for producing your own parts are (I've paraphrased them from the article here):

  • The aircraft has been out of production for years
  • The aircraft is an orphan without a Type Certificate
  • There is no technical support because the aircraft is so old
  • There may be long delays in getting parts from the manufacturer
  • The price of official parts is extremely high

As for requirements of the part itself, the article list four characteristics that a part must have:

  1. The part must be properly designed
  2. The part must be produced to conform to the design
  3. The part's production must be properly documented
  4. The part must be properly maintained

The owner must be involved in the production but doesn't actually have to do the manufacturing himself:

The aircraft owner must participate in the manufacture of the part in at least one of five ways for it to be considered an Owner Produced Part.

  1. The owner provides the manufacturer of the part with the design or performance data.
  2. The owner provides the manufacturer of the part with the materials.
  3. The owner provides the manufacturer with fabrication processes or assembly methods.
  4. The owner provides the manufacturer of the part with quality control procedures.
  5. The owner personally supervises the manufacture of the new part.

More recently, in the September 2014 edition of the Cessna Pilots Association magazine, Mike Busch has an article on replacement parts that calls the current regulations on owner produced parts "extremely liberal":

“Owner-produced parts” do not require a PMA. These are parts produced by an aircraft owner for use on his own aircraft, and not offered for sale. There is an FAA letter of interpretation that sets forth precisely what an owner's involvement must be to qualify a part as “owner-produced,” and it is extremely liberal. The owner need not actually manufacture the part himself, so long as he provides specifications or materials or supervision or some other meaningful participation in the part's production.

Unfortunately, he didn't mention exactly which letter of interpretation covers these parts but the FAA magazine article refers to an "FAA Memorandum dated August 5, 1993" and I guess it's probably the same one. I wasn't able to find it on the FAA site.

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