Towards safe human–machine interaction in remotely controlled ships: A system-theoretic risk analysis framework

With the rapid advancement of Maritime Autonomous Surface Ships (MASS), the complexity of onboard automation and remote operations has significantly increased, placing greater demands on the safety and reliability of Human-Machine Interaction (HMI). Ensuring safe navigation under varying levels of autonomy requires a structured and comprehensive assessment of HMI-related risks. This study proposes a novel risk-informed safety framework for HMI in remotely controlled MASS, particularly those operating at Degree of Autonomy 2 (DoA2). By integrating Systems-Theoretic Process Analysis (STPA) with the Human Factors Analysis and Classification System (HFACS), the framework systematically identifies unsafe interactions, causal factors, and control structure vulnerabilities across multiple functional levels. The approach captures both technical failures and human factors, offering a holistic view of HMI safety. A case study of DoA2 ships demonstrates the applicability and effectiveness of the proposed STPA-HFACS framework in visualising unsafe scenarios and tracing their root causes. The findings highlight key areas for risk mitigation through targeted technological improvements and enhanced operator training. This research contributes a structured methodology for MASS HMI safety assessment and provides practical guidance for risk management in semi-autonomous ship operations.