This paper presents the viewpoint that an air traffic management system is emergent, i.e., exhibiting behaviors at the system-wide level that emerge from the combined actions of individuals within the system. Emergence carries with it the additional implication that these phenomena typically cannot be predicted by examining the individuals' behavior alone. As a result, this paper proposes agent-based simulation as a method of predicting the impact of revolutionary changes to an air transportation system. Agent based simulation can integrate cognitive models of human performance, physical models of technology behavior and description of their operating environment. Simulation of these individual models acting together can predict the result of completely new transformations in procedures and technologies. While agent-based simulations cannot include every aspect of system behavior, they can provide quick, cost-effective insights that can supplement other forms of analysis.