Editorial Note on Part 21
Editorial Notes: 1. For miscellaneous amendments to cross references in this 21 see Amdt. 21-10, 31 FR 9211, July 6, 1966. 2. Nomenclature changes to part 21 appear at 74 FR 53384, Oct. 16, 2009.

§ 21.17 Designation of applicable regulations. ( a ) Except as provided in §§ 25.2, 27.2, and 29.2 of this subchapter, and in parts 26, 34, 36, and 38 of this subchapter, an applicant for a type certificate must show that the aircraft, aircraft engine, or propeller concerned meets— ( 1 ) The applicable requirements of this subchapter that are effective on the date of application for that certificate unless— ( i ) Otherwise specified by the FAA; or
( ii ) Compliance with later effective amendments is elected or required under this section; and
( 2 ) Any special conditions prescribed by the FAA.
( b ) For special classes of aircraft, including the engines and propellers installed thereon (e.g., gliders, airships, and other nonconventional aircraft), for which airworthiness standards have not been issued under this subchapter, the applicable requirements will be the portions of those other airworthiness requirements contained in Parts 23, 25, 27, 29, 31, 33, and 35 found by the FAA to be appropriate for the aircraft and applicable to a specific type design, or such airworthiness criteria as the FAA may find provide an equivalent level of safety to those parts.
( c ) An application for type certification of a transport category aircraft is effective for 5 years and an application for any other type certificate is effective for 3 years, unless an applicant shows at the time of application that his product requires a longer period of time for design, development, and testing, and the FAA approves a longer period.
( d ) In a case where a type certificate has not been issued, or it is clear that a type certificate will not be issued, within the time limit established under paragraph (c) of this section, the applicant may— ( 1 ) File a new application for a type certificate and comply with all the provisions of paragraph (a) of this section applicable to an original application; or
( 2 ) File for an extension of the original application and comply with the applicable airworthiness requirements of this subchapter that were effective on a date, to be selected by the applicant, not earlier than the date which precedes the date of issue of the type certificate by the time limit established under paragraph (c) of this section for the original application.
( e ) If an applicant elects to comply with an amendment to this subchapter that is effective after the filing of the application for a type certificate, he must also comply with any other amendment that the FAA finds is directly related.
( f ) For primary category aircraft, the requirements are: ( 1 ) The applicable airworthiness requirements contained in parts 23, 27, 31, 33, and 35 of this subchapter, or such other airworthiness criteria as the FAA may find appropriate and applicable to the specific design and intended use and provide a level of safety acceptable to the FAA.
( 2 ) The noise standards of part 36 applicable to primary category aircraft.
[Doc. No. 5085, 29 FR 14564, Oct. 24, 1964, as amended by Amdt. 21-19, 32 FR 17851, Dec. 13, 1967; Amdt. 21-24, 34 FR 364, Jan. 10, 1969; Amdt. 21-42, 40 FR 1033, Jan. 6, 1975; Amdt. 21-58, 50 FR 46877, Nov. 13, 1985; Amdt. 21-60, 52 FR 8042, Mar. 13, 1987; Amdt. 21-68, 55 FR 32860, Aug. 10, 1990; Amdt. 21-69, 56 FR 41051, Aug. 16, 1991; Amdt. 21-70, 57 FR 41367, Sept. 9, 1992; Amdt. 21-90, 72 FR 63404, Nov. 8, 2007; Doc. No. FAA-2015-1621, Amdt. 21-100, 81 FR 96688, Dec. 30, 2016; Amdt. No. 21-107, 89 FR 12653, Feb. 16, 2024]