Multiple Cooperative UAS Mid-Air Collision Probability Assessment and Monte-Carlo Validation in Urban Air Mobility

Risk assessment is pivotal for enabling unmanned aircraft systems (UAS) in urban airspace, particularly under high-density, cooperative flight operations. This paper presents a systematic approach to quantifying the mid-air collision (MAC) risk for cooperative UAS in urban air mobility (UAM) by incorporating flight characteristics, operational uncertainties, and latency effects. We propose a novel MAC evolution timeline comprising three safety barriers (strategic, tactical, and conflict avoidance mitigation) designed to prevent conflicts from culminating in a collision. Guided by this timeline, the failure of strategic mitigation is captured through a conflict probability estimation model, which includes an analytical solution for rapidly identifying threats. The failure of tactical mitigation is then evaluated via an approach time estimation model that integrates multiple maneuver strategies to refine outcome predictions. Finally, conflict avoidance failure is characterized using the risk ratio associated with detection and avoidance (DAA) systems. By combining the failure probabilities of these three safety barriers, we derive the overall MAC probability. Monte Carlo simulations validate the proposed models, revealing that the resulting probability curves closely match the theoretical predictions.