This paper examines the nature and characteristics of the US airport hierarchy and compares the size distribution of air-traffic communities with the urban hierarchy, using data from 1997. Air-carrier network structures have a significant influence on the distribution of traffic in the US hierarchy, and it is demonstrated that there is greater variability in the relationship between traffic and urban population at the top and bottom sections of the hierarchy than for medium-sized communities. Small communities are examined in detail with economic and demographic characteristics of 'Essential Air Service' communities being presented. It is demonstrated that the subsidised communities are generally located in areas of lower economic growth and lie further from the larger air-traffic hubs than unsubsidised communities.