This paper addresses the problem of congestion prevalent in most airports around the world, especially at security screening and check-in areas of departure terminals due to rapid growth in civil aviation demand.  Addressing this problem is often limited by space and financial constraints, making layout optimization the most feasible option available.  However, misestimating space needs due to a common misuse of international standards for space requirements at different levels of service (LOS) renders many re-layout projects ineffective.  This factor coupled with an inefficient initial layout are found to be the main reasons behind the high congestion experienced at Beirut-Rafic Hariri International Airport (BEY) departure terminal during peak season demand, making it an ideal candidate for a case study on terminal layout optimization.  Therefore, this paper presents a macroscopic system dynamics model to depict the overall flow of departing passengers at the BEY passenger terminal and uses dwell time as a variable in the model to assess and re-allocate existing space needs in the departure terminal for minor investment costs.  The value of this research is in providing a decision support tool for airport operators to improve passenger flow in the terminal within existing space constraints and for minimum investment costs.