There is an increasing need to fly Unmanned Aircraft Systems (UAS) in the U.S. National Airspace System (NAS) for national security, defense, emergency management, science missions, and future commercial applications. Because UAS operations have not been integrated with the civilian airspace, research is needed to identify and develop new safety analysis approaches, prognostic indicators, and potential safety metrics to enable seamless operation and integration of UAS into the NAS. IAI and its subcontractors, Luxhoj Consulting and Research LLC (LCR) and Coherent Technical Services Incorporated (CTSI), are developing an Uninhabited Aerial System (UAS) Safety Analysis Model (USAM). USAM is a ground-breaking technology that combines prior NASA research on future UAS flights and UAS performance profiles, with technologies developed specifically for UAS flight risk analysis and NAS-wide simulation analysis. USAM computes the probability of collisions between piloted and UAS aircraft while performing a full hazard analysis for a range of possible collisions, resulting in a risk profile for UAS operations in the NAS. This risk profile can be used to decide what procedures or technologies should be developed to mitigate the risks and render UAS operations as safe as, or safer than, piloted flights. USAM consists of three interacting components: a screening tool to identify situations where loss of separation might occur, a stochastic computational engine for computing the conditional probabilities of collision, and a Bayesian belief network for establishing the causal links for each collision, thereby identifying the hazards. Specific UAS-piloted flight encounter geometries have already been studied. In this program, different UAS traffic levels will be modeled, and specific conflict scenarios will be studied to provide a comprehensive view of the spectrum of possible hazards .