[Code of Federal Regulations] [Title 14, Volume 2] [Revised as of January 1, 2008] From the U.S. Government Printing Office via GPO Access [CITE: 14CFR137.21] [Page 1191-1192] TITLE 14--AERONAUTICS AND 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 [[Page 1192]] certificate that is suspended or revoked shall return it to the Administrator.