This research memo presents results obtained during the period from July 1 through October 1, 1975, in research on a systems analysis procedure for estimating the capacity of an airport in which both airside and landside capacities are studied. A definition of the system is presented including the system boundaries and a description of the subsystems and components of the overall system. A review is made of available analytical models of airport components including air traffic control, runways, gates, passenger processing baggage claim, internal roadways, and parking lots. Also included is a discussion of previous concepts and definitions of capacity, a discussion of relevant units of capacity, and a proposed definition of capacity for the airport system as a whole as well as its subsystems and components.