Investigation of Strategies for Optimal Collaborative Airborne Separation in Free Flight

Abstract

The limitations of the existing air traffic management (ATM) system lead to problems like congestion in airspace, delays and improper detection of conflicts between the aircrafts and their resolution. The current trend is to shift from this centralized system to an autonomous one in which the assurance of separation lies with the aircraft themselves. This self separation concept is termed as Free Flight. In this study we deal with the two most important concepts in Free Flight – conflict detection and resolution (CDR). Conflicts can be resolved using either a change in altitude, heading or speed of the aircraft involved, or a combination of these. Results of three speed control actions for optimal conflict resolution for a cluster of three aircraft involved in a conflict scenario are reported in literature. To study the effectiveness of these control actions, we propose a penalty function containing four control parameters, whose values can be changed. In this function, penalties are imposed only during those time intervals in which either the separation distance falls below the minimum prescribed value, and/or in which the aircraft is forced to fly at a speed that is different from the desired optimal value, in order to resolve a conflict. The Penalty that results for nine different combinations of the values of four penalty parameters for each of the three conflict avoidance solutions has been studied. The results indicate a nearly linear increasing trend in the net penalty values in some of the cases for the initial conflict configuration and for all the cases in the three conflict avoidance solutions. The net penalty values for the initial conflict configuration almost increase by a factor of two in the cases where one penalty parameter is changed while keeping the other constant. Further, the range of variation in the minimum and the maximum net penalty values for each of the three conflict avoidance solutions was seen to be quite large. Lower net penalty values were observed for cases in which all the three aircraft co-operate in the conflict resolution process.