[Code of Federal Regulations] [Title 47, Volume 5] [Revised as of October 1, 2002] From the U.S. Government Printing Office via GPO Access [CITE: 47CFR87.71] [Page 203] TITLE 47--TELECOMMUNICATION COMMISSION (CONTINUED) PART 87--AVIATION SERVICES--Table of Contents Subpart C--Operating Requirements and Procedures Sec. 87.71 Frequency measurements. A licensed operator must measure the operating frequencies of all land-based transmitters at the following times: (a) When the transmitter is originally installed; (b) When any change or adjustment is made in the transmitter which may affect an operating frequency; or (c) When an operating frequency has shifted beyond tolerance.