Study on Impact of Separation Distance to Traffic Management for Small UAS Operations in Urban Environment

Unlike manned aviation operating in non-segregated or controlled airspace where separation distance between aircraft is well defined, the safe separation distance for UAVs operating in urban environment in segregated or uncontrolled airspace have yet to be established. There are many confounding factors affecting the safe separation distance for UAV. These include but not limited to exogenous factors such as wind, rain and birds. In this study, the aim is to derive the relationship between separation distance and the number of conflicts. As a preliminary study, direct flights for UAVs are considered. This is because from a UAS operator's point of view, a direct flight to destination is always preferred. However this may not be allowed due to the potential increase in conflicts due to multiple UAVs operating concurrently in the airspace. If the airspace density is sufficiently low, one expects the conflicts between UAVs to be reduced accordingly, thus making direct paths feasible. On the other hand, a high density would nonetheless increase the number of conflicts, rendering a controlled and managed airspace necessary, either by altering the flight paths or through speed control. It is then postulated that there should be a particular threshold whereby such transition from a free flight path to a non-free flight path will take place. With this aim in mind, the number of conflicts, defined by the loss of separation, between the UAVs is investigated for two scenarios: (1) direct flight path to destination and (2) direct flight path with speed control. In both scenarios, the UAVs will enter the airspace simultaneously towards different destination points, simulating the maximum possible number of UAVs entering the airspace at the same time. The number of conflicts is also then computed for different values of distance separation distance separation for each scenario. These results will then give a preliminary hint on the threshold conditions for the transition.