Development of unmanned aerial systems (UAS), made of an unmanned aerial vehicle (UAV) and equipment such as a ground station, has increased tremendously in recent years. This has made more pressing the need for new design methodologies that provide a reliable and thorough safety assessment throughout the entire design process. The European specific operations risk assessment (SORA) document provides recommended operational safety objectives (OSO) to achieve. The current paper lays groundwork to comply with OSOs pertaining to UAS flight procedures. Key criteria for modeling such procedures are identified and lead to the choice of the AltaRica DataFlow (ADF) language. The Cecilia Workshop is used to model three real-life UAS emergency flight procedures. Custom components developed for this model are presented while discussing the process of modeling a formal procedure from an informal text source. A safety analysis is performed on the resulting model by computing minimal cut sets on an undesired procedure outcome. The results are then reviewed, providing feedback to increase the procedures' safety gain.