The Gulf Regional Airspace Strategic Initiative (GRASI) is an effort to involve stakeholders affected by future changes in the airspace and military installations in the Northwest Florida Panhandle in creating a compromise that equally protects each stakeholder's airspace and airfield resources now and into the future. As part of this effort, the Gulf Regional Airspace Strategic Initiative ExtendSim discrete event model was developed, aiming to expand on the capabilities of existing modeling tools used for GRASI by creating higher fidelity estimates on transit times along airspace paths, and by introducing airport models. Creating additional modeling capabilities makes the model a more effective tool for evaluating alternatives put forth by military and civilian stakeholders. The GRASI ExtendSim model was used to evaluate two scenarios, and found a slight, but significant change in flying time by military aircraft. This model creates a framework from which future models can be developed for the GRASI effort. / Master of Science