14 C.F.R. § 26.1 – Purpose and scope.

(a) This part establishes requirements for support of the continued airworthiness of and safety improvements for transport category airplanes. These requirements may include performing assessments, developing design changes, developing revisions to Instructions for Continued Airworthiness (ICA), and making necessary documentation available to affected persons. Requirements of this part that establish standards for design changes and revisions to the ICA are considered airworthiness requirements.
(b) Except as provided in paragraph (c) of this section, this part applies to the following persons, as specified in each subpart of this part:
1. (1) Holders of type certificates and supplemental type certificates.
2. (2) Applicants for type certificates and supplemental type certificates and changes to those certificates (including service bulletins describing design changes).
3. (3) Persons seeking design approval for airplane repairs, alterations, or modifications that may affect airworthiness.
4. (4) Holders of type certificates and their licensees producing new airplanes.
(c) An applicant for approval of a design change is not required to comply with any applicable airworthiness requirement of this part if the applicant elects or is required to comply with a corresponding amendment to part 25 of this chapter that is adopted concurrently or after that airworthiness requirement.
(d) For the purposes of this part, the word “type certificate” does not include supplemental type certificates.