This paper proposes a new high-accuracy calculation method to estimate collision probability to ground obstacles during Instrument Landing System (ILS) approach. The current collision risk model (CRM) used to evaluate the ground obstacle collision probability was developed in the 1970s. In this CRM, a shadowing technique is used to avoid over-estimation of the risk when there are multiple obstacles located close to each other. However, this shadowing still overestimates the risk due to several conservative assumptions. This paper proposes mathematical modifications to the calculation of shadowing to address the risk overestimation. To validate the proposed method, 106 sets of aircraft trajectories are generated so that the actual risk can be estimated by counting the number of collisions. The result shows that the risk calculated by the proposed method is much closer to the actual risk compared to the one calculated by the current CRM. The proposed model will help introduce ILS approach at obstacles-sensitive airports.
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