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.

(c) Nothing in this section shall be deemed to require air carriers to permit smoking aboard aircraft.