Before revision: 21.303 PMA Approval It is generally illegal in the United States to install replacement or modification parts on a certificated aircraft without an airworthiness release such as PMA .
After revision: 21.303 a Supplemental Type Certificate (STC) or Parts Manufacturing Approval (PMA) Approval It is generally illegal in the United States to install replacement or modification parts on a certificated aircraft without an airworthiness release such as PMA .