ARgument-based airworthiness assurance of small UAS

A combination of airworthiness and various operational restrictions are currently used to assure that unmanned aircraft system (UAS) operations can be conducted at an acceptable level of safety. We present a methodology to communicate these aspects in a unified way, providing a centralized record of safety risk management (SRM) activities. Central to our approach is the notion of structured argument, i.e., an explicit chain of reasoning linking safety substantiating evidence to the overall safety and airworthiness objectives. Our use of argumentation is motivated, in part, by the observations that: i) certain kinds of UAS operations currently require a safety case; ii) structured arguments are often a core component of modern safety cases, providing a convenient means to represent the underlying reasoning and to access the aggregated safety information; and iii) there exists a standardized graphical notation to present structured arguments, i.e., the goal structuring notation (GSN), which has been used in both civil and military aviation. To exemplify our methodology, we apply it to an unmanned rotorcraft system (URS), using GSN arguments to show the relationship between safety of URS operations, and various SRM measures including airworthiness, in particular a potential certification basis for type design assurance. The example illustrates how our approach can coexist with, and augment, existing safety processes by transforming SRM artifacts into assurance argument fragments.