12.1 Part 21 Certification Framework: TC, PC, PMA, TSO & Owner-Produced Parts

12.1 Part 21 Certification Framework: TC, PC, PMA, TSO & Owner-Produced Parts

[!IMPORTANT] The parts eligibility question: Every time an IA signs an approval for return to service, the signature implicitly certifies that the parts installed are eligible for that aircraft. There is no separate FAA form that says "eligible." Eligibility is established by tracing the part back to a Part 21 approval and forward to the aircraft's approved configuration. This section is the tracing map.

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The Approval Architecture

14 CFR Part 21, Certification Procedures for Products and Articles, is the rule that creates every approval an IA relies on. The structure is worth holding in one picture:

                 TYPE CERTIFICATE (design approval)
                    |                         |
                    |                         +--> SUPPLEMENTAL TYPE CERTIFICATE
                    |                              (major change to type design)
                    v
      PRODUCTION CERTIFICATE (approval to build to that design)
                    |
                    v
      AIRWORTHINESS CERTIFICATE (this individual aircraft conforms
                                 and is in condition for safe operation)

  Articles / parts:
      PMA  -- Parts Manufacturer Approval: design + production approval
              for a replacement or modification part
      TSO  -- Technical Standard Order authorization: design + production
              approval that the article meets a minimum performance standard

• Type certificate (TC) approves the design. Under § 21.41 the type certificate includes the type design, the operating limitations, the type certificate data sheet, the applicable regulations, and any other conditions prescribed — which is why the TCDS is evidence that the product is type certificated.
• Production certificate (PC) approves the manufacturing system that reproduces that design.
• Supplemental type certificate (STC) approves a major change to a type design that is not so extensive as to require a new type certificate application (Section 4.3).
• Airworthiness certificate attaches to the individual aircraft.

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14 CFR 21.303: Replacement and Modification Parts

Section 21.303 is the provision the IAR test asks about by number: which location in 14 CFR provides for the fabrication of aircraft replacement and modification parts? The answer is 14 CFR Part 21, Subpart K, § 21.303.

The rule's structure is a general requirement plus a set of exceptions. The general requirement is that no person may produce a modification or replacement part for sale for installation on a type certificated product unless it is produced under a Parts Manufacturer Approval (PMA). Then come the categories to which the PMA requirement does not apply:

Two of these deserve their own treatment because they are where mistakes happen.

Owner-Produced Parts

The exception is narrow and every word of it does work: produced by an owner or operator for maintaining or altering that owner's or operator's own product.

• The part must be for the owner's own aircraft. It cannot be produced for sale, for another owner, or as shop stock.
• The owner must participate in the production — the FAA's position is that the owner must take part in at least one of controlling the design, producing the part, providing the materials, providing the specifications, or supervising the production. A mechanic cannot simply manufacture a part and label it owner-produced.
• The part must still conform to the type design and meet § 43.13(b), so the owner-produced exception is about who may produce it, not about relaxing the design standard.
• The part is not marked with a PMA and carries no 8130-3, so its pedigree is established by the aircraft's own maintenance records. A thorough Item 8 or logbook entry describing the part, its material, and the data it was produced from is what makes the part defensible three owners later.

Standard Parts

A standard part conforms to an established industry or U.S. government specification that includes design, materials, manufacture, and uniform identification requirements, and that is published so that any party can make the part. AN, MS, and NAS hardware are the everyday examples, which is why a bag of AN3 bolts carries no PMA marking and needs none. Note the boundary: a part is standard because it conforms to a published specification, not because it is common or inexpensive. Hardware-store bolts are not standard parts in this sense (Section 2.3).

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PMA and TSO: What Each Approval Actually Means

Parts Manufacturer Approval

A PMA is a combined design and production approval for a replacement or modification part. It is granted for a specific part on a specific list of products, and that eligibility list is the operative document for the IA. A PMA part is marked with "FAA-PMA" along with the part number and the make and model of the products it is eligible for.

The IA's check is straightforward: is this aircraft make and model on the PMA eligibility list? A PMA part that is eligible for a Cessna 172 is not thereby eligible for a Cessna 182.

Technical Standard Order Authorization

A TSO is a minimum performance standard for an article. A TSO authorization (TSOA) is a design and production approval stating that the manufacturer's article meets that standard.

The distinction the exam tests: a TSO authorization is not, by itself, approval to install the article on a given aircraft. It establishes that the article performs to a standard. Installation eligibility comes from the aircraft's type design, an STC, or an approved alteration. So an inspector who finds a TSO'd article installed still has to ask what data approved the installation.

TSO articles also come up in a different form on the IAR test: when the question is which document establishes the test standard for a particular article — for example, the compressive load test standard for a seat belt — the answer is the TSO that the article was built to, rather than an STC (which approves an installation) or a PMA (which approves production of a replacement part).

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Part 183: Designees Who Produce Approved Data

14 CFR Part 183, Representatives of the Administrator, allows the FAA to designate private persons to act on its behalf. The designee that matters most to an IA is the one that produces approved data for repairs and alterations:

So the answer to "Part 183 allows the FAA to designate certain persons to develop and approve technical data for alteration and repair of U.S. certificated aircraft — these persons are known as..." is Designated Engineering Representatives. A DAR issues certificates; a DMIR works production conformity; only the DER (and the ODA engineering unit) approves alteration and repair data.

And as Section 5.3 establishes: a DER approves data, never the aircraft. The return to service remains with the IA, the repair station, or the manufacturer.

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Parts Eligibility Decision Path for the IA

   Part in hand
        |
        +-- Marked FAA-PMA?  --> Check the eligibility list for THIS make/model
        |
        +-- Marked TSO?      --> Article meets a performance standard.
        |                        Now ask: what data approves its INSTALLATION here?
        |
        +-- OEM part with 8130-3 or manufacturer C of C?
        |                     --> Check part number against the IPC / TCDS
        |
        +-- Standard part (AN/MS/NAS to a published spec)?
        |                     --> Acceptable; verify the correct spec and size
        |
        +-- Owner-produced?  --> Verify owner participation, conformity to type
        |                        design, and a records entry that documents it
        |
        +-- None of the above, no traceability
                              --> Suspected Unapproved Part. Do not install;
                                 do not approve for return to service (Section 5.3)

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High-Yield Exam Traps

• § 21.303 is the parts-fabrication provision. Not § 23 Appendix B, not § 45.21.
• Owner-produced means the owner participated, and the part is for the owner's own aircraft.
• A TSO authorization is not installation approval. It approves the article against a performance standard.
• A PMA is product-specific. Check the eligibility list against this make and model.
• DERs approve data; DARs issue certificates; DMIRs work production conformity.
• Standard parts are standard because a published specification exists, not because they are common.