Current models for airport terminal performance assessment require substantial modeling effort to be customized to the configuration of a particular airport terminal and to reflect adequately the alternative airport operational policies adopted in a user-friendly way. Therefore, there is a need to develop a generic, yet flexible decision-support tool that will facilitate high-level decision-making related to fundamental changes in the structure and operation of the airport terminal system. This paper presents a generic and easily customizable system dynamics based tool for assessing the performance of the Athens International Airport passenger terminal under different demand and resource deployment scenaria.