Quantifying Well Clear for Autonomous Small UAS

Air traffic safety is the primary concern when it comes to the integration of Unmanned Aircraft Systems in the civil airspace. At the tactical level, the goal is to quantify en-route safety through pairwise separation minima. Unmanned Aircraft Systems make use of Detect and Avoid systems to remain, or regain well clear from other aircraft. There is already a well clear definition adopted for large Unmanned Aircraft Systems, however, this definition is not adequate and applicable to small Unmanned Aircraft Systems operating in low altitudes. In order to ensure the safe separation of various types of sUAS with different performances, a self-separation method is proposed. The method is based on dynamic protection zone, an early concept developed by US Air Force and later adapted into a time-based Detect and Avoid self-separation method. This paper outlines an engineering approach on designing a generic methodology, to define well clear among small Unmanned Aircraft Systems. For this purpose, both unmanned aircraft and systems performance are considered. Furthermore, we specify and recommend appropriate well clear thresholds and Detect and Avoid alerting times, based on the results the severity of loss of well clear. Several influencing factors such encounter geometry, speed and uncertainties in Communication, Navigation and Surveillance systems are examined to obtain efficient separation criteria.