As a determinant of the air passenger's choice of airport, ground accessibility plays a more dominant role than air carrier level-of-service. Thus, the use of differential flight frequencies as a policy tool to shift air passengers from one airport to another would have only limited potential. These conclusions are based upon an empirical study of air passengers' choice of airport in which a series of multinomial logit models were calibrated using air passenger survey data. These models relate the probability that a given airport will be selected to measures of ground accessibility and air carrier level-of-service associated with each available departure airport. A variety of measures for ground accessibility and air carrier level-of-service were tested in various combinations in models which consistently performed well from a statistical standpoint and in which the ground access measure was consistently the dominant variable.