In the last years, Unmanned Aircraft Systems (UASs) are getting popular and are widely used to provide many applications. Specifically, a promising UAS application discussed in this thesis is the distribution of life-saving pharmaceutics using UASs. This thesis aims at defining a path planning strategy to be used to provide the distribution of life-saving pharmaceutics using UASs in populated areas. The proposed strategy is based on a method already suggested in the literature by the research group, consisting in two phases: first, a risk-map is generated analyzing the risk of a specific area; then, a path planning algorithm based on the well-known Rapidly-exploring Random Trees (RRT) algorithm searches for the optimal path that minimizes the overall risk and the flight time.