To address the problem of collision risk assessment for mixed operations of unmanned aerial vehicles and manned aircraft in integrated airspace, this paper proposes a collision risk analysis method based on an improved Event model. Based on the traditional Event model, the proposed method introduces modifications from four aspects: collision-box geometric modeling, data-link delay, wake vortex effect, and multi-layer safety barrier reliability. Specifically, an elliptical cylindrical collision box is used to replace the conventional rectangular collision box; a 5s data-link delay correction and a 200m wake vortex distribution distance correction are introduced; and a multi-layer safety barrier reliability model based on a series-parallel structure is established. Meanwhile, a position error probability distribution model based on the normal distribution assumption and overlap probability integral expressions are supplemented to improve the theoretical framework. Taking the crossing routes of the AT200 large fixed-wing UAV and a CITIC Offshore Helicopter near Shenzhen Nantou Airport as a typical case, collision risks in the vertical, longitudinal, and lateral directions are calculated, and the analytical model is verified through 100000 Monte Carlo simulations. The results show that a vertical separation of 150m can reduce the risk to 0.41 events per million flight hours, representing an approximately 80% reduction compared with the risk at a 130m separation. A critical threshold exists at a longitudinal separation of 120m, and a longitudinal safety separation of no less than 300m is recommended. The lateral risk exhibits a double-peak characteristic: the first peak occurs at approximately 110m, corresponding to the main rotor downwash influence region, while the second peak occurs at approximately 135m, corresponding to the lateral diffusion region of the tail rotor vortex. Therefore, a lateral separation of no less than 200m is recommended. The parameter sensitivity analysis indicates that the vertical error standard deviation has the greatest influence on collision risk, with a sensitivity index of 0.92. The Monte Carlo simulation results show that the relative errors between the analytical solutions and the simulation results are all within 10%, demonstrating good model accuracy. The research findings can provide theoretical reference for the formulation of safety separation standards in integrated airspace.
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