[Code of Federal Regulations] [Title 14, Volume 2] [Revised as of January 1, 2003] From the U.S. Government Printing Office via GPO Access [CITE: 14CFR137.21] [Page 769] TITLE 14--AERONAUTICSAND SPACE CHAPTER I--FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION (CONTINUED) PART 137--AGRICULTURAL AIRCRAFT OPERATIONS--Table of Contents Subpart B--Certification Rules Sec. 137.21 Duration of certificate. An agricultural aircraft operator certificate is effective until it is surrendered, suspended, or revoked. The holder of an agricultural aircraft operator certificate that is suspended or revoked shall return it to the Administrator.