Unmanned Air Systems (UAS) have numerous applications. Commercial potential in particular will not be realized until a comprehensive strategy is developed for safely and fully integrating UAS into an airspace currently dominated by commercial transport operations. This paper overviews a challenging benchmark application, on-demand surveillance over a densely-populated urban region, then presents a spectrum of risks that might be encountered. We describe novel risk mitigation criteria for small UAS that focus not on vehicle preservation but instead on minimizing risk of harm to people and property on the ground as well as to higher-value airborne assets. We conclude with a case study in which wind shear and turbulence in an urban canyon require a small UAS to execute an unplanned landing.