In the air transport sector where the uncertainty is very frequent due to the high sensitivity of the activity to many factors that influence the behavior of the consumers. Fuzzy logic can be used to produce estimates which take into account the vagueness of the operating environment. In this sector, many important decisions about the supply of service are based on these estimates. In this paper an analysis of the optimal supply conditions under fuzzy demand information is considered for a market where only one carrier is operating. The carrier's supply decision making process is investigated, first when the demand function is obtained through classical methods then when it is given by a fuzzy function. The main advantages of the new approach are then discussed.