(SEE ALSO... CAP Products and Services)
Before we discuss the CAP procedures, we should get educated on this topic . The best information I have seen on this subject is the following article, originally published in the Aviation Maintenance Technology trade publication.
by Bill O'Brien
Along with the pilot shortage and the mechanic shortage, there is  also a  parts shortage that plagues the general aviation industry. Because  supply and  demand are out of balance the cost of new and used parts seem to  increase every  day. Let's examine the reasons why this is so.  
First, we have an old fleet. The average general aviation (GA)  single engine  airplane is approximately 32 years old. The average age of GA  multi-engine  reciprocating aircraft is close to 27 years old. The average age for the  turbine  powered multi-engine propeller driven aircraft average out around 19  years of  age. So because of long term wear and tear the demand for replacement  parts and  large sub-assemblies is much greater today than it was even 10 years  ago.  
The second reason is our general aviation fleet has been well  maintained over  the years. So well maintained in fact, the average GA aircraft with a  mid-time  engine and decent avionics has appreciated to two or three times its  original  purchase price and is still climbing. Yet even in that land of many  zeros the  older aircraft are still substantially lower in price than the cost of a  brand  new aircraft with similar performance numbers and equipment. So the  value of  older aircraft in good shape are proven investments that over time have  beaten  the DOW JONES average. So we have an economic imperative on the part of  the  owners to keep maintaining older aircraft in flying condition which  increases  the demand for replacement parts.  
The third reason is the increasing production costs to make a  part. Today  aircraft manufacturers are not making makes and models of aircraft in  the same  quantity they made them back in the Seventies. So the production runs  for parts  are not as frequent and not as many parts are produced. In addition, it  is not  cost effective for a manufacturer to make a lot of parts even if the  unit price  for each part is out of this world because taxes on maintaining a large  inventory of parts would eat all of the profits. This low parts  production keeps  the supply of replacement parts low.  
The fourth reason is that some manufacturers would prefer that  their older  makes and model aircraft-made a million years ago-would quietly  disappear from  the aircraft registry. This retroactive birth control on the part of the   manufacturers may seem not to make any sense until you look at aircraft  market  dynamics of creating demand and reducing costs. First, each older  aircraft that  is no longer in service creates a demand for a new, more expensive  aircraft to  take its place. Second, despite some tort claim relief granted to GA  manufacturers in the early Nineties, the fewer older aircraft there are  in  service, the manufacturers of those aircraft enjoy reduced overall  liability  claims and ever decreasing continuing airworthiness responsibilities. 
So how are we going to maintain these older aircraft with an ever  dwindling  parts supply when Part 21, section 21.303 Replacement and modification  of parts,  requires us to use the Parts Manufactured Approval (PMA) parts on a type   certificated product? Well, the same rule grants four exemptions to the  PMA  requirement.  
1. You can use parts produced under a type or production  certificate such as  a Piper, Cessna, or Mooney produced part; 
2. A owner or operator produced part to maintain or alter their  own product;  
3. Parts produced under a Technical Standard Order (TSO) such as  radios, life  vests and rafts, and GPS; or,  
4. A standard aviation part such as fasteners, washers, or safety  wire. 
Before I segue into the subject of "owner produced parts" as  called out in  section 21.303, which is the purpose of this article. I would like to  create a  small uproar with this statement: "FAA Airframe and Powerplant rated  mechanics  can maintain, repair, and modify parts, but they cannot make a brand new  part  and call it a repair." Before you accuse me of losing dendrites by the  minute,  check out section 65.81 General privileges and limitations. The section  talks  about maintenance, preventive maintenance, and alterations, but not the  manufacturing of parts. Nor is it an implied privilege in Part 65,  because Part  21 section 21.303 says "no person" may make a replacement part for a  type  certificated (TC) product unless that person has a PMA, etc.  
While I write this I can remember 25 pounds ago and when I had  hair, I worked  in the real world and I specialized in making engine baffles for  Lycoming  engines. Before someone accuses me of bureaucratic ventriloquism which  is  roughly translated as "talking out of both sides of my mouth." My weak  defense  is, I made the parts because I thought I could." It never dawned on me  that I  could not legally make a part. Some of you may be astounded that I make  this  confession freely. It's no big thing because I know the statue of  limitations  has run out years ago and a jury of my peers would never look me in the  eye and  convict me.  
So here is our problem that we must solve. Since mechanics cannot  legally  make parts for aircraft and aircraft need replacement parts, how are we  going to  keep the fleet flying? If we cannot find PMA, TSO, standard, or  production  holder replacement parts, we are left to make the part under the  owner-produced  option under section 21.303(b)(2). However, we must remember that the  part is  for the owner/operator's aircraft only and is not manufactured for sale  to other  TC aircraft. 
To get through confusing regulatory policy with our pride intact,  let's try  the question and answer routine. (Note: This policy is taken from FAA 's  AGC-200  policy memorandum to AFS-300 on the definition of "Owner-Produced Parts"  dated  August 5, 1993) 
Question 1: Does the owner have to manufacture the part him or  herself in  order to meet the intent of the rule? 
Answer 1: No, the owner does not have to make the part him or  herself.  However to be considered a producer of the part he/she must have  participated in  controlling the design, manufacturer, or quality of the part such as: 
1. provide the manufacturer with the design or performance data  from which to  make the part, or 2. provide the manufacturer with the materials to make the part, or
3. provide the manufacturer with fabrication processes or assembly methods to make the part, or
4. provide the quality control procedures to make the part, or
5. personally supervised the manufacturer of the part.
Question 2: Can the owner contract out for the manufacture of the  part and  still have a part that is considered "owner-produced?" 
Answer 2: Yes, as long as the owner participated in one of the  five functions  listed in Answer 1. 
Question 3: Can the owner contract out the manufacture of the  part to a  non-certificated person and still have a part that is considered  "owner-produced?" 
Answer 3: Yes, as long as the owner participated in one of the  five functions  listed in Answer 1. 
Question 4: If a mechanic manufactured parts for an owner, is  he/she  considered in violation of section 21.303(b)(2)? 
Answer 4: The answer would be no, if it was found that the owner  participated  in controlling the design, manufacture, or quality of the part. The  mechanic  would be considered the producer and would not be in violation of  section  21.303(a). On the other hand, if the owner did not play a part in  controlling  the design, manufacture, or quality of the part, the mechanic runs a  good chance  of being in violation of section 21.303 (b)(2). 
Question 5: What kind of advice can you give on how a mechanic  can avoid even  the appearance of violating section 21.303(b)(2)?  
Answer 5: First, a mechanic should never make a logbook or  maintenance entry  saying that he/she made a part under his certificate number. This foopah  will  send up a flare and get you undue attention from your local FAA  inspector, which  you could do without. However, the mechanic can say on the work order  that he  helped manufacture an owner-produced part under section 21.303 (b)(2).  
Second, the owner or operator should be encouraged to make a log  book entry  that is similar to section 43.9 maintenance entry that states: The part  is  identified as an owner produced part under section 21.303 (b)(2). The  part was  manufactured in accordance with approved data. The owner/operator's  participation in the manufacturer of the part is identified, such as  quality  control. The owner must declare that the part is airworthy and sign and  date the  entry.  
Question 6: Is there anything else a mechanic must do? 
Answer 6: The mechanic must ensure that the owner-produced part  meets form,  fit, and function, and, within reasonable limits, ensure that the part  does meet  its approved type design (e.g. like looking at the approved data used to  make  the part). Then the mechanic installs the part on the aircraft, makes an   operational check if applicable, and signs off the required section 43.9   maintenance entry.  
Question 7: What is the owner responsible for and what is the  mechanic  responsible for concerning owner-produced parts? 
Answer 7: The owner is responsible for the part meeting type  design and being  in a condition for safe operation. The mechanic is responsible for the  installation of the owner-produced part being correct and airworthy and  for a  maintenance record of the installation of the part made.  
Question 8: How does the owner or operator get the approved data  to make a  part if the manufacturer and other sources are no longer in business? 
Answer 8: For aircraft that the manufacturer is no longer  supporting the  continuing airworthiness of, the owner or operator can petition the FAA  Aircraft  Certification Directorate under the Freedom of Information Act for the  data on  how the part was made. Or the owner or operator can reverse engineer the  part  and have the data approved under a FAA field approval or, if it is a  really  complicated part, have the data approved by a FAA engineer or FAA  Designated  Engineering Representative. 
Question 9: What happens to the owner-produced part on the  aircraft if the  original owner sells the aircraft? 
Answer 9: Unless the part is no longer airworthy, the original  owner-produced  part stays on the aircraft.  
I hope that I spread some light on the murky subject of  owner-produced parts,  so the next time instead of saying to the owner of an broke aircraft:  "Sure, 'I'  can make that part," you will now say "Sure, 'WE' can make that part."  
Bill O'Brien is an Airworthiness Aviation Safety Inspector in FAA's Flight Standards Service. This article also appeared in the Aircraft Maintenance Technology magazine.


