14 C.F.R. § 252.4
Air carriers shall prohibit smoking on the following flights:
(b) Nonscheduled passenger flights, except for the following flights where a flight attendant is not a required crewmember on the aircraft as determined by the Administrator of the Federal Aviation Administration:
[Docket DOT-OST-2011-0044, 81 FR 11427, Mar. 4, 2016]