What is the Difference Between FAA PMA Parts and FAA STC Parts?

A member recently asked “what is the difference between FAA PMA parts and FAA STC parts.”

A PMA is a production approval.  14 C.F.R. § 21.1(b)(7).  The PMA gives the holder the power to produce articles for use on aircraft.  E.g. 14 C.F.R. § 21.9(a)(2).  Parts produced under an FAA PMA are approved parts.

A supplemental type certificate (“STC”) is a design approval only.  14 C.F.R. § 21.1(b)(4).  It does not provide any inherent production approval.  Thus, an STC holder who wants to produce articles for use on aircraft will need some other production basis (in addition to the STC).  When parts are offered for sale and described as “STC Parts” it is important for the buyer to understand the production approval basis for the parts.

STC Holder Options for Production

Generally speaking, if a person knows that a replacement or modification article is reasonably likely to be installed on an aircraft, engine or propeller, then the person may only produce that article under one of the categories listed in the FAA regulations – specifically in section 21.9(a) of those regulations. These represent the FAA-acceptable mechanisms for production.

STC holders can and do use production certificate (PC) and/or parts manufacturer approval (PMA) to obtain FAA production approval for parts where the design has been approved under an STC.  14 C.F.R. § 21.9(a)(2).  In these cases, the production approval permits the holder to produce articles that are likely to be installed on aircraft, engines or propellers.

An STC holder (or the licensee of such a holder) could produce parts for consumption during maintenance or alteration.  14 C.F.R. § 21.9(a)(6).  But if that company decides to sell those parts, instead of consuming them itself, then that may violate the regulations.  14 C.F.R. § 21.9.

An owner/operator could produce an article for maintaining or altering that owner or operator’s own aircraft, engine or propeller.  4 C.F.R. § 21.9(a)(5).  An STC could serve as the design basis for the article.  So this is another possible way to produce parts based on STC data.

It is also possible for an article that is called-out in an STC design to be produced as a commercial part or a standard part; but when such articles are produced under one of these categories, they are typically not called “STC parts.”

Conclusion

I have seen situations where STC holders mistakenly believe that they have the authority to produce and sell aircraft parts under the STC (alone).  This is, of course, not true.

Because of this history, whenever someone tells me they intend to buy STC parts, I always want to follow-up to identify the production approval basis of the parts.