[Code of Federal Regulations] [Title 14, Volume 4] [Revised as of January 1, 2006] From the U.S. Government Printing Office via GPO Access [CITE: 14CFR252.9] [Page 206] TITLE 14--AERONAUTICS AND SPACE CHAPTER II--OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) PART 252_SMOKING ABOARD AIRCRAFT--Table of Contents Sec. 252.9 Ventilation systems. Air carriers shall prohibit smoking whenever the ventilation system is not fully functioning. Fully functioning for this purpose means operating so as to provide the level and quality of ventilation specified and designed by the manufacturer for the number of persons currently in the passenger compartment.