Application of “Well Clear” to Small Drones

Detect and avoid systems (DAA) play an important role in more and more areas of manned and unmanned aviation. Originally developed as an additional safety concept for manned aviation, today they represent a central concept of unmanned aviation, without which many deployment scenarios would not be conceivable. DAA systems perceive the environment using sensors such as lidar, radar or cooperative transponders to detect and avoid surrounding traffic. A core concept here is the notion of “Well Clear”. Originally this described the intuitive awareness of the pilot of a safe, conflict-free situation. In the context of semi-automatic systems, however, this term had to be formalized, not least by the standardization of ACAS/TCAS. This resulted in several, partly mutually compatible definitions. We present different approaches to the concept of “Well Clear”, including RTCA DO-365 and latest U-space developments. Further, we apply the notion to application scenarios involving small drones, and discuss to what degree the definitions can be applied or have to be modified in order to grant both safety and effectiveness.