Testing Operating Procedures for Large UAS with Detect and Avoid Capabilities in Civil Air Traffic Management Environments

The Royal Netherlands Aerospace Center (NLR), in partnership with General Atomics Aeronautical Systems, Inc. (GA-ASI) and Information Systems Delft (ISD), has conducted several series of human-in-the-loop simulation experiments to assess and refine the safety and efficiency of fully integrating operations of large uncrewed aircraft systems (UAS) into typical civil air traffic scenarios. These experiments used a high-fidelity Air Traffic Control (ATC) simulation facility to provide professional controllers and pilots with the experience of introducing large UAS operations into otherwise familiar air traffic situations. Currently, there are no UAS operating approvals that would allow such tests to be conducted in the real world, so the experience gained and lessons learned are invaluable in preparing for safe and smooth introduction of large UAS into civil airspace operations in the near future.Detect and Avoid (DAA) technologies are key to allowing nonsegregated, beyond visual line-of-sight (BVLOS) operation of large UAS, by enabling their remote pilots to keep the universal right of way rules of the air, without the conventional ability to see out of the aircraft's cockpit. The focus of these experiments, therefore, has been to test DAA capabilities and operating procedures needed for remote pilots and air traffic controllers to maintain separation of the uncrewed aircraft (UA) from other aircraft and to avoid collisions. Scenarios were carefully designed to trigger DAA alerting and guidance to the remote pilot, requiring a response with appropriate procedures, including coordination with ATC, to assess the safety and operational efficiency of those procedures. Many of the scenarios required traffic to make procedural mistakes in order to create conflict geometries that would trigger DAA alerts. UAS contingencies were also incorporated, such as loss of C2 link, to evaluate remote pilot and controller response procedures.GA-ASI's SkyGuardian, a turboprop-powered, large fixed-wing UAS, was used as the performance model for a UAS operating from conventional runways that could perform flights as diverse as infrastructure surveying to cargo transport. Rotterdam airport and its surrounding airspace was selected as the operating context, to typify moderately busy and complex European airspace. The UAS flight scenarios spanned all the typical domestic airspace ATC roles, involving Tower, Approach and Route controllers, and included typical background commercial and general aviation traffic patterns and densities.The DAA capabilities tested are based on RTCA DO-365B Minimum Operational Performance Standards (MOPS). Earlier series of experiments tested the capabilities of a Class 1 system with air-to-air radar, active surveillance, ADS-B In and DAA alerting and guidance for en-route self-separation, plus Class 5 for DAA alerting and guidance in the terminal area. The latest series of experiments upgraded the DAA system to Class 2 capabilities with the addition of TCAS II collision avoidance logic, also with automatic execution of TCAS Resolution Advisories by the UA. A new operating mode was also added for Cockpit Display of Traffic Information (CDTI)-assisted visual separation (CAVS), to test the efficiency and effectiveness of procedures for controllers to delegate separation responsibility to the remote pilot during the landing approach. Operating procedures were initially based on those described in the Operational Services Environment Description appendix of RTCA DO-365B.The professional participants provided qualitative assessment of several human factors aspects for each scenario and the procedures employed, including their perceptions of safety, operational acceptability, situational awareness and workload. The experiments proved that appropriately-equipped UAS can be introduced safely into the existing airspace system, and that controllers adapt quickly to the few unique considerations needed when managing UAS traffic. The DAA system gave remote pilots unprecedented traffic awareness compared to conventional incockpit situations, enabling them to identify potential conflicts at a similar time to ATC, or even before. This situation emphasized the need for procedures that support efficient coordination between remote pilots and ATC, to avoid contrary resolutions to the same identified conflict. Beneficial changes to DAA procedures were also identified that would improve overall safety and operational efficiency. For example, by providing more options when responding to traffic alerts in the terminal area, and to ensure that remote pilots follow all right of way rules, for predictability when responding to DAA alerting and guidance. Furthermore, when the UA executes an automatic Resolution Advisory while in the Lost C2 Link state, controllers expressed a preference for the UA to return automatically to its approved lost link altitude, after becoming clear of the conflict, to minimize the incidence of secondary conflicts and to reduce controller workload. These findings and others will be fed back to RTCA committees to further improve DAA MOPS.