[Code of Federal Regulations] [Title 14, Volume 2] [Revised as of January 1, 2007] From the U.S. Government Printing Office via GPO Access [CITE: 14CFR91.173] [Page 526] TITLE 14--AERONAUTICS AND SPACE CHAPTER I--FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION (CONTINUED) PART 91_GENERAL OPERATING AND FLIGHT RULES--Table of Contents Subpart B_Flight Rules Sec. 91.173 ATC clearance and flight plan required. No person may operate an aircraft in controlled airspace under IFR unless that person has-- (a) Filed an IFR flight plan; and (b) Received an appropriate ATC clearance.