FASR: Automated Identification of Unsafe Control Actions in STPA

2026-05-28

AI Summary

This study addresses the limitations of existing System-Theoretic Process Analysis (STPA) methods, which rely heavily on manual effort for identifying Unsafe Control Actions (UCAs), resulting in low efficiency and susceptibility to human error. To overcome these challenges, this work proposes the first integration of robustness analysis into the STPA framework, combining model-driven engineering with formal methods to enable automated and complete UCA identification. The approach was validated through a case study on an aircraft braking control system, demonstrating significant improvements in both analytical efficiency and accuracy. Furthermore, user studies indicate that the accompanying tool offers practical utility for the majority of safety analysts, supporting its real-world applicability in safety-critical systems engineering.

Abstract

The System-Theoretic Process Analysis (STPA) is a well-established hazard analysis technique that has been applied to a wide range of safety-critical systems. Despite its popularity, there is relatively little automation support for STPA, and most of its steps are carried out manually by a human analyst, which can be time consuming and error prone. This paper investigates the potential use of model-based engineering and formal methods to assist human analysts in efficiently and accurately carrying out STPA. The proposed tool, called FASR (Formalizing and Automating STPA with Robustness), enables automated, complete identification of unsafe control actions (UCAs), leveraging recent advances in robustness analysis to identify UCAs as undesirable deviations in the controller's actions. The use of the tool is demonstrated on a case study involving a Braking System Control Unit (BSCU) in an avionics system. As a preliminary exploration of the potential benefits and limitations of the tool, the paper reports on a user study involving nine participants with varying backgrounds in STPA, model-based engineering, and formal methods; the study found that most participants considered the tool a useful aid in identifying UCAs, while suggesting improvements that would make a tool such as FASR usable and applicable to a wider range of systems and analysts.

Problem

• STPA
• unsafe control actions
• automation
• hazard analysis
• formal methods

Innovation

• STPA automation
• unsafe control actions
• formal methods
• model-based engineering
• robustness analysis