National airspace sector occupancy and conflict analysis models for evaluating scenarios under the free-flight paradigm

Free-Flight is a paradigm of aircraft operations that permits the selection of more cost-effective routes for flights rather than simple traversals between designated way-points, from various origins to different destinations. In this paper, we consider the effect of this paradigm on sector workloads and potential conflicts or collision risks, based on current and projected levels of commercial air traffic. To accomplish this task, we first develop an Airspace Sector Occupancy Model (AOM) that identifies the occupancies of flights within three-dimensional (possibly nonconvex) regions of space called sectors, by utilizing an iterative procedure to trace each flight's progress through sector modules, that constitute the sectors. Next, we develop an Aircraft Encounter Model (AEM), which uses the information obtained from AOM to efficiently estimate the number and nature of blind-conflicts (i.e., conflicts under no avoidance or resolution maneuvers) resulting from a selected mix of flight plans. Besides identifying the existence of a conflict, AEM also provides useful information on the severity of the conflict and its geometry, such as the faces across which an intruder enters and exits the protective shell or envelope of another aircraft, the duration of intrusion, its relative heading, and the point of closest approach. For purposes of evaluation and assessment, we also develop a metric that provides a summary of the conflicts in terms of severities and difficulty of resolution. Finally, we apply these models to real data provided by the Federal Aviation Administration (FAA) for evaluating several Free-Flight scenarios under wind-optimized conditions. This study constitutes the first phase of a project undertaken by a joint FAA/Eurocontrol Collision Risk Modeling Group to develop tasks for investigating air traffic control strategies and related workload and collision risk consequences under various scenarios. Follow-on work will incorporate pilot blunders, random deviations, and air traffic control man-in-the-loop maneuvers within the context of the Free-Flight paradigm, using the basic tools developed in the present study.