[Code of Federal Regulations] [Title 14, Volume 1] [Revised as of January 1, 2006] From the U.S. Government Printing Office via GPO Access [CITE: 14CFR21.99] [Page 134] 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 D_Changes to Type Certificates Sec. 21.99 Required design changes. (a) When an Airworthiness Directive is issued under Part 39 the holder of the type certificate for the product concerned must-- (1) If the Administrator finds that design changes are necessary to correct the unsafe condition of the product, and upon his request, submit appropriate design changes for approval; and (2) Upon approval of the design changes, make available the descriptive data covering the changes to all operators of products previously certif icated under the type certificate. (b) In a case where there are no current unsafe conditions, but the Administrator or the holder of the type certificate finds through service experience that changes in type design will contribute to the safety of the product, the holder of the type certificate may submit appropriate design changes for approval. Upon approval of the changes, the manufacturer shall make information on the design changes available to all operators of the same type of product. [Doc. No. 5085, 29 FR 14567, Oct. 24, 1964, as amended by Amdt. 21-3, 30 FR 8826, July 24, 1965]