§ 135.121
Alcoholic beverages.
(a) No person may drink any alcoholic beverage aboard an aircraft unless the certificate holder operating the aircraft has served that beverage.
(b) No certificate holder may serve any alcoholic beverage to any person aboard its aircraft if that person appears to be intoxicated.
(c) No certificate holder may allow any person to board any of its aircraft if that person appears to be intoxicated.