Strictly Formalized Situation-Operator-Modeling technique for fall-back layer modeling for autonomous or semi-autonomous systems requiring software-based fail-safe behavior

Autonomous and semi-autonomous aerial systems (AES) are often needed to perform tasks in complex and dynamic environments. The safe navigation assurance as well as safety assurance of AES are open research issues. Traditional combination of safety aspects with mission related tasks and in consequence unmanageable AES system complexity as well as unpredictable effects during the spatial environment interaction makes traditional safety assurance methods inapplicable. This paper introduces Strictly Formalized Situation-Operator-Modeling (sf-SOM) technique for AES safe behavior assurance. In combination with the System Safety Surveillance and Control (SSSC) system concept a AES fall-back layer concept can be realized. In comparison to other approaches, in this concept a separation between regular behavior generating mission-tasks and safety assurance non-mission tasks is used. Furthermore, the system is separated in well-defined, safety task-specific modules and can be realized using standardized industrial programming languages and programmable safety device. Proof of concept using an industrial Programmable Logic Controller demonstrates the successful use of SSSC-based fall-back layer also for comparable applications.