## 4 Conclusions  
The paper reported some exemplary experimental results obtained through real-time validation, with hardware and human in the loop (RTS-HIL) simulations of an automatic ADS-B-based separation assurance and collision avoidance system (ASACAS) aimed to support RPAS automatic operations and remote pilot decision making. The paper described the background, motivation, and design steps that led to the development, implementation, and testing of the ASACAS. In addition, the paper provided a description of the concept of operations of the system and of its architectural organization, and it summarized the main concepts implemented in the system, identifying its main functions and their mutual connection in the overall integrated system. From the description of the exemplary real-time simulation with hardware and pilots in the loop tests (including both separation assurance and collision avoidance test scenarios) and from the analysis and discussion of the related results, it emerged that the ASACAS behaved as expected in the tests: it was demonstrated to be able to support the remote pilot in performing the separation management task at a tactical level and to be able to perform automatic collision avoidance at the emergency level. The elaborated maneuvers, both for self-separation and for collision avoidance, were able to minimize the deviation from the original flight path while also being able to prevent an infringement of the assigned safety volumes. The self-separation maneuver was designed according to early feedback and suggestions provided by the very experienced test pilots that acted as remote pilots. In particular, the separation assurance functionality of the ASACAS was designed to provide maneuvers that preferably act on only one flight dimension (longitudinal, lateral, or speed), with an assigned priority to lateral changes (track deviation)--a priority that is, in all cases, a parameter that can be set as desired. This design choice changed the initial implementation of the functionality, where the design was aimed to obtain 4D maneuver, and was motivated by the need to provide the pilot with a minimum amount of workload in evaluating and implementing the proposed maneuver. From such perspective, it is much more convenient for the pilot to manage a suggested maneuver that only affects one flight dimension than a whole 4D maneuver. Therefore, the conflict resolution functionality assigns specified priority to the possible resolution maneuvers in order to select the one that minimizes the workload for the remote pilot; when this is not possible due to a particular conflict scenario, the system increases the maneuver complexity up to a full 4D maneuver. This is a relevant added value of the system. Future work will address many possible improvements of the system. It is currently designed to be used in the en-route phase of a flight, and its extension to TMA operations is a future improvement of the system. In addition, the collision avoidance functionality of the system is limited to sequential single-collision management and does not specifically take into account the rules of the air and self-compatibility requirements. Therefore, future improvements will be needed to address these important aspects. Finally, as indicated in the introductory part of the paper, the system has also been validated in real flight trials that will be the subject of future publications. Both authors contributed extensively to the research activities presented in this paper. [PERSON] prepared and reviewed all sections of the paper, [PERSON] specifically prepared Sections 3.2 and 3.3. All authors have read and agreed to the published version of the manuscript. The real-time simulation campaigns described in this paper were co-financed by the SESAR Joint Undertaking through the project RAID, as part of RPAS Demo projects of the SESAR Program. The ASACAS design was carried out in the framework of the nationally-funded Italian projects MISE and EATS.