Scale-free Networks and Commercial Air Carrier Transportation in the United States

Network science, or the art of describing system structure, may be useful for the analysis and control of large, complex systems. For example, networks exhibiting scale-free structure have been found to be particularly well suited to deal with environmental uncertainty and large demand growth. Changes in the demand for air transportation are inevitable, and indeed seem to be upon us. The National Airspace System (NAS) improvement initiatives currently being pursued are focused on incremental improvements in today’s Air Transportation System (ATS), but it is becoming clear these will not satisfy future demand. In June of 2001, Federal Aviation Administration (FAA) spokesman William Shumann told the San Francisco Chronicle, “Even if the [FAA] plan attains the goal of a 30 percent increase in air traffic, it will not completely close the gap between supply and demand... There is no obvious solution.” More dramatically, Transportation Secretary Norm Minetta recently called for tripling the air traffic capacity of the United States in the next 15 to 20 years because of growing demand in the airline sector and the introduction of new transportation modes such as jet taxies and unmanned aerial vehicles. He stated, “The changes that are coming are too big, too fundamental for incremental adaptation of the infrastructure... We need to modernize and transform our global transportation system, starting right now.” The National Airspace System may be, at least in part, a scalable network. In fact, the hub-and-spoke structure of the commercial segment of the NAS is an often-cited example of an existing scale-free network After reviewing the nature and attributes of scale-free networks, this assertion is put to the test: is commercial air carrier transportation in the United States well explained by this model? If so, are the positive attributes of these networks, e.g. those of efficiency, flexibility and robustness, fully realized, or could we effect substantial improvement?