On Metrics for U-Space Safety Risk Assessment

Regulatory frameworks are essential to ensure safe (i.e., collision-free) and efficient operations of UAVs. In Europe, U-Space addresses these needs through traffic management services. However, to maximize the effectiveness of these services in preventing and mitigating safety risks, particularly the risk of collision, a comprehensive safety risk assessment is necessary. This assessment involves determining and calculating safety metrics that are vital for measuring and monitoring the Target Level of Safety (TLS) in U-Space, enabling timely mitigation actions when collision risks arise. This paper presents several safety metrics, categorizing them into collision and surveillance performance metrics. It proposes a systematic approach to identify the most effective safety metrics for assessing safety risks in U-Space. Through experiments conducted under varying conditions (e.g., traffic density and GPS failures), the study calculates the correlation between collision frequency-recognized as a key risk indicator-and other safety metrics. The results show that metrics like probability of update, probability of long gaps, bubble violations, false/true target reports, false track density, and vertical position accuracy show strong correlations with safety risk level. These findings highlight that our approach is effective in identifying safety metrics that provide valuable in-sights for monitoring, preventing, and mitigating risks associated with UAVs' operations in the context of U -Space,