Aircraft to Aircraft Collision Risk Modeling

The increase in new surveillance and communication technologies that are becoming available across different airspaces drives the need to reassess the collision risk modeling (CRM) that informs separation standards. The impact of new surveillance, communication, and navigation technologies is being investigated for oceanic and remote airspaces, terrestrial air transport operations, and new entrant operations, such as advanced air mobility (AAM). For oceanic and remote airspace risk assessment, CRM has previously focused on models which rely on a probability distribution of aircraft locations within an airspace. These models have typically assessed risk per lateral or longitudinal dimension based on the historic paradigm of oceanic operations. Many of these airspaces apply separation standards based on the CRM results in the form of establishing appropriately spaced track systems such as the North Atlantic Organised Track System (NAT-OTS). In recent years, many airspaces are moving away from this type of airspace management and providing more opportunity for route-free flight. In order to provide new separation standards that could support non-track-based flight trajectories, the modeling has evolved into a more dynamic, radial approach that relies on the specific location of aircraft. Another key aspect of this CRM is the addition of the effect of communication and surveillance capabilities which allows for the inclusion of pilot and controller intervention should an off-nominal event, such as an unplanned deviation, occur. The capability to include navigation, communication, and surveillance within the CRM has resulted in a model that is highly adaptable to the various technologies available. The CRM work presented in this paper was initially developed as the foundation for the first oceanic and remote airspace non-procedural separation which will be published by ICAO in 2024. Subsequently, this more direct aircraft-to-aircraft CRM was adapted to a wide variety of other airspace types, vehicles, and operations. The mathematical details of this model and the adaptation methodology are thoroughly described in this paper.