[Code of Federal Regulations] [Title 14, Volume 1] [Revised as of January 1, 2007] From the U.S. Government Printing Office via GPO Access [CITE: 14CFR21.120] [Page 138] TITLE 14--AERONAUTICS AND SPACE CHAPTER I--FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION PART 21_CERTIFICATION PROCEDURES FOR PRODUCTS AND PARTS--Table of Contents Subpart E_Supplemental Type Certificates Sec. 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]