As unmanned aircraft systems (UAS) become more important to the US military and other users, the pressure to allow them to fly in the national airspace increases. The greatest impediment to this is the lack of an alternative means of compliance with federal “see and avoid” regulations to provide the capability to avoid airborne conflicts between the UAS and manned aircraft. To provide this alternative means of compliance, the US Army is leading the development of a Ground-Based Sense and Avoid System (GBSAA). The system uses ground-based radars, threat detection and alerting logic, and decision support display aids to provide an air picture of the UAS’s operating environment and follows the DO-254 and DO-178C standards for safety critical avionics hardware and software, respectively. This system will allow greater airspace access and lower cost operations by replacing ground observers in the field with a centralized system, thus consolidating the observer function. The first GBSAA deployment site is expec...