14 CFR § 252.4 - Smoking ban: air carriers.
Air carriers shall prohibit smoking on the following flights:
(a) Scheduled passenger 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:
(1) Single entity charters.
(2) On-demand services of air taxi operators.