A Distributed Trajectory-Oriented Approach to Managing Traffic Complexity

Abstract

In order to handle the expected increase in air traffic volume, the next generation air transportation system is moving towards a distributed control architecture, in which ground-based service providers such as controllers and traffic managers and air-based users such as pilots share responsibility for aircraft trajectory generation and management. While its architecture becomes more distributed, the goal of the Air Traffic Management (ATM) system remains to achieve objectives such as maintaining safety and efficiency. It is, therefore, critical to design appropriate control elements to ensure that aircraft and groundbased actions result in achieving these objectives without unduly restricting user-preferred trajectories. This paper presents a trajectory-oriented approach containing two such elements. One is a trajectory flexibility preservation function, by which aircraft plan their trajectories to preserve flexibility to accommodate unforeseen events. And the other is a trajectory constraint minimization function by which ground-based agents, in collaboration with air-based agents, impose just-enough restrictions on trajectories to achieve ATM objectives, such as separation assurance and flow management. The underlying hypothesis is that preserving trajectory flexibility of each individual aircraft naturally achieves the aggregate objective of avoiding excessive traffic complexity, and that trajectory flexibility is increased by minimizing constraints without jeopardizing the intended ATM objectives. The paper presents conceptually how the two functions operate in a distributed control architecture that includes self separation. The paper illustrates the concept through hypothetical scenarios involving conflict resolution and flow management. It presents a functional analysis of the interaction and information flow between the functions. It also presents an analytical framework for defining metrics and developing methods to preserve trajectory flexibility and minimize its constraints. In this framework flexibility is defined in terms of robustness and adaptability to disturbances and the impact of constraints is illustrated through analysis of a trajectory solution space with limited degrees of freedom and in simple constraint situations involving meeting multiple times of arrival and resolving a conflict.

Trajectory Planning by Preserving Flexibility: Metrics and Analysis

“…A previous effort analyzed the solution space along a path using speed as the only degree of freedom and with RTA and conflict constraints. 15,16,17 This analysis extends that research to the solution space for an aircraft with only heading as a degree of freedom and with RTA and conflict constraints.…”

“…15,16 Examples of these constraints include the heading limits, RTAs, and loss of separation, described in the previous section, but in general they include any constraints that intend to achieve ATM and aircraft objectives. They define the trajectory solution space as was shown in Figure 5.…”

“…15,16 Trajectory flexibility preservation plans the trajectory in a manner that affords the aircraft sufficient flexibility in accommodating disturbances that stem, for example, from other traffic or from weather activity. Flexibility preservation complements separation assurance both within the conflict resolution horizon and outside it within an extended flexibility planning horizon.…”

“…As discussed in , although flexibility preservation does not explicitly coordinate between the aircraft, it assists each ownship in reducing the risk of conflict due to the potential behavior of the surrounding traffic, thus resulting in implicit coordination. 15 Beyond the conflict resolution horizon, the flexibility preservation function plans the aircraft trajectory to minimize its exposure to disturbances such as weather cells and dense traffic areas. It is hypothesized that trajectory flexibility preservation naturally produces traffic situations that are less complex than without its application.…”

“…To help support this hypothesis trajectory flexibility metrics have been defined in previous work to represent the trajectory robustness and adaptability to the risk of violating safety and traffic management constraints. 15,16 It is also hypothesized that minimizing the constraints imposed on a trajectory, without jeopardizing the intended ATM objectives, increases its flexibility. These functions offer a trajectory-oriented approach to managing traffic complexity, by explicitly planning aircraft trajectories, from the ground or the air, such that their contribution to complexity is minimized.…”