This paper discusses problems encountered in modeling airport activity and particularly emphasizes forward planning and policy making. It is concerned with the relations among airlines, airports, and users (passengers and freight). Three simple models of activity are indicated, dealing successively with capacity, investment, and pricing. A basic need is creating a workable typology of airports in which attributes other than size may be considered. A second requirement is considering the importance of fluctuations in airport output. We used multivariate analysis of data for the leading British airports in the period 1968 to 1972 to develop a successful typology, which is essentially applicable to other national airport systems. It stresses the differences between scheduled and nonscheduled activity. Correlations among definitive output variables are used as input to principal components and factor analysis to derive the typology. Output is then disaggregated by the use of a corrected moving mean to give seasonal and trend components. These are used for analyzing growth and growth variability and for studying the stability over time of seasonal variations. In addition, we note positive links between nonscheduled activity and output variability. The implications for planning are demonstrated, in particular the close association among nonscheduled activity, variability, and predictability. The variable associations also indicate possible investment scenarios for the airport manager and the airport modeler.

This paper considers a number of problems associated with building a fundamental dynamic system model of airport activity. At first sight, such activities as movements, passenger throughput, and financial turnover might appear to vary solely as a function of airport size. We examine this possibility, which would permit size variables to provide the basic structure of a simple system model, and also examine whether there is a valid alternative methodology for developing an activitybased system model. Moreover, we examine the amount