  Employing Unmanned Aircraft Systems (UAS) beyond visual line of sight (BVLOS)
is an endearing and challenging task. While UAS have the potential to
significantly enhance today's logistics and emergency response capabilities,
unmanned flying objects above the heads of unprotected pedestrians induce
similarly significant safety risks. In this work, we make strides towards
improved safety and legal compliance in applying UAS in two ways. First, we
demonstrate navigation within the Probabilistic Mission Design (ProMis)
framework. To this end, our approach translates Probabilistic Mission
Landscapes (PML) into a navigation graph and derives a cost from the
probability of complying with all underlying constraints. Second, we introduce
the clearance, explanation, and optimization (CEO) cycle on top of ProMis by
leveraging the declaratively encoded domain knowledge, legal requirements, and
safety assertions to guide the mission design process. Based on inaccurate,
crowd-sourced map data and a synthetic scenario, we illustrate the application
and utility of our methods in UAS navigation.
