Making a Risk Informed Safety Case for Small Unmanned Aircraft System Operations

This paper describes an approach to create a Risk Informed Safety Case (RISC) towards facilitating safe, cost-effective operations with small unmanned aircraft systems (sUAS). The core constituents of a RISC are i) barrier models of safety, which underpin the development of a comprehensive collection of safety measures so as to be commensurate with the safety risk posed, and ii) structured arguments, which provide assurance of safety in operations through explicit rationale and the appropriate evidence. We also identify key safety-related assurance concerns that are relevant for improving confidence in a RISC, and, in turn, in operational safety. Then, we present a tiered framework to structure the corresponding assurance arguments. This work, which has been motivated, in part, by an absence of the relevant aviation regulations and applicable performance standards, leverages our successful, collective prior experience in creating RISCs for real sUAS operations. We draw upon this background to provide illustrative examples of our approach.