MetroSim is a Metroplex-based arrival, departure, and surface optimization. Linking with both the NASA-developed Traffic Management Advisor (TMA) tool as well as the NASA-developed System Oriented Runway Management (SORM) tool, MetroSim allows airport planners, traffic flow management experts, airline dispatchers, air traffic controllers, and pilots to reduce the uncertainty in operations planning, recover quickly from disruptive events, maintain high throughput even in adverse weather conditions, and handle the uncertainties associated with weather forecasts. To accomplish all these goals simultaneously, the MetroSim architecture contains a collection of different tools, some of which are simulations, some of which are physics-based computations, and some of which are mathematical optimization calculations. These tools all interoperate in a distributed computational environment to provide real-time airport planning and optimization at the Metroplex level for all operationsarrivals, departures, and surface movements. The type of each tool is chosen to be the best and fastest at what it is required to compute.