14 CFR § 21.120 - Responsibility of supplemental type certificate holders to provide written permission for alterations.

---
identifier: "/us/cfr/t14/s21.120"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "14 CFR § 21.120 - Responsibility of supplemental type certificate holders to provide written permission for alterations."
title_number: 14
title_name: "Aeronautics and Space"
section_number: "21.120"
section_name: "Responsibility of supplemental type certificate holders to provide written permission for alterations."
chapter_name: "FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION"
subchapter_number: "C"
subchapter_name: "AIRCRAFT"
part_number: "21"
part_name: "CERTIFICATION PROCEDURES FOR PRODUCTS AND ARTICLES"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "42 U.S.C. 7572; 49 U.S.C. 106(f), 40105, 40113, 44701-44702, 44704, 44707, 44709, 44711, 44713, 44715, 45303."
cfr_part: "21"
---


# 21.120 Responsibility of supplemental type certificate holders to provide written permission for alterations.

A supplemental type certificate holder who allows a person to use the supplemental type certificate to alter an aircraft, aircraft engine, or propeller must provide that person with written permission acceptable to the FAA.

[Doc. No. FAA-2003-14825, 71 FR 52258, Sept. 1, 2006]