Operational research has been developed and introduced into air transportation problems since the late 1940s, mainly in the U.K. and the U.S.A., and simulation techniques have also been used for designing or evaluating air traffic control systems. Some data on the actual operations are needed for carrying out these studies. The data on the time and motion of taxiing aircraft, especially jet aircraft, were collected at Tokyo International Airport (TIA) in 1975 and 1976 and the relation between average taxi speed and taxi distance was stated on the basis of the observed data. In this paper, a theoretical method for estimating the average taxi speed of departing aircraft is considered, using simplified models, and the results are compared with the empirical data.