Husni Idris

Operational Concept for Collaborative Traffic Flow Management based on Field Observations

*† ‡ § ** Based on field observations conducted at a wide range of airline operational control (AOC) facilities and the Traffic Management Unit (TMU) of several Air Route Traffic Control Centers , a human-centered, bottom-up approach was followed to develop a future concept of operation for local/tactical en route collaborative traffic flow management (TFM). Many operational issues were recorded for different types of flow constraints and the interaction between the TMU and AOC in dealing with these situations was observed. Several key traffic flow management issues were identified that caused inefficiencies in current operations (in terms of performance metrics such as delay, workload, equity, and user preferences), despite the best efforts of dispatchers and flow managers. The operational concept provides a framework for enhancing collaboration between TMUs and AOCs to mitigate these flow management issues. One key observation was that, due to high TMU workload, the interaction between the TMU and AOC is limited in current tactical TFM operations to addressing user concerns in extreme circumstances such as emergency and low fuel load. The concept of operation suggests extending the scope of TMU-AOC collaboration to start in the early stages of tactical TFM planning and continue through implementation.

Distributed traffic complexity management by preserving trajectory flexibility

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. This paper presents preliminary research investigating a distributed trajectory oriented approach to manage traffic complexity, based on preserving trajectory flexibility. The underlying hypotheses are that preserving trajectory flexibility autonomously by aircraft naturally achieves the aggregate objective of avoiding excessive traffic complexity, and that trajectory flexibility is increased by collaboratively minimizing trajectory constraints without jeopardizing the intended air traffic management objectives. This paper presents an analytical framework in which flexibility is defined in terms of robustness and adaptability to disturbances and preliminary metrics are proposed that can be used to preserve trajectory flexibility. The hypothesized impacts are illustrated through analyzing a trajectory solution space in a simple scenario with only speed as a degree of freedom, and in constraint situations involving meeting multiple times of arrival and resolving conflicts.

A Distributed Trajectory-Oriented Approach to Managing Traffic Complexity

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.

Preliminary Benefits Assessment of Traffic Aware Strategic Aircrew Requests (TASAR)

While en route, aircrews submit trajectory change requests to air traffic control (ATC) to better meet their objectives including reduced delays, reduced fuel burn, and passenger comfort. Aircrew requests are currently made with limited to no information on surrounding traffic. Consequently, these requests are uninformed about a key ATC objective, ensuring traffic separation, and therefore less likely to be accepted than requests informed by surrounding traffic and that avoids creating conflicts. This paper studies the benefits of providing aircrews with on-board decision support to generate optimized trajectory requests that are probed and cleared of known separation violations prior to issuing the request to ATC. These informed requests are referred to as traffic aware strategic aircrew requests (TASAR) and leverage traffic surveillance information available through Automatic Dependent Surveillance – Broadcast (ADS-B) In capability. Preliminary fast-time simulation results show increased benefits with longer stage lengths since beneficial trajectory changes can be applied over a longer distance. Also, larger benefits were experienced between large hub airports as compared to other airport sizes. On average, an aircraft equipped with TASAR reduced its travel time by about one to four minutes per operation and fuel burn by about 50 to 550 lbs per operation depending on the objective of the aircrew (time, fuel, or weighted combination of time and fuel), class of airspace user, and aircraft type. These preliminary results are based on analysis of approximately one week of traffic in July 2012 and additional analysis is planned on a larger data set to confirm these initial findings.

Trajectory Planning by Preserving Flexibility: Metrics and Analysis

In order to support traffic management functions, such as mitigating traffic complexity, ground and airborne systems may benefit from preserving or optimizing trajectory flexibility. 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. In this paper these metrics are instantiated in the case of planning a trajectory with the heading degree of freedom. A metric estimation method is presented based on simplifying assumptions, namely discrete time and heading maneuvers. A case is analyzed to demonstrate the estimation method and its use in trajectory planning in a situation involving meeting a time constraint and avoiding loss of separation with nearby traffic. The case involves comparing path-stretch trajectories, in terms of adaptability and robustness along each, deduced from a map of estimated flexibility metrics over the solution space. The case demonstrated anecdotally that preserving flexibility may result in enhancing certain factors that contribute to traffic complexity, namely reducing proximity and confrontation.

Task Analysis for Feasibility Assessment of a Collaborative Traffic Flow Management Concept

*† ‡ § A far-term collaborative traffic flow management concept has been proposed for mitigating flow constraint situations that result in imbalance between demand and capacity in the National Airspace System. This paper presents a scenario-based task analysis of core attributes of the concept in the expected future traffic environment. These attributes include a dynamic allocation of some traffic flow management responsibility to airline operation centers, while the traffic flow managers maintain a supervisory role, monitoring performance and intervening increasingly as time-to-constraint decreases. This analysis proposes a three-tier time horizon with different collaboration schemes between traffic flow managers and airlines within each tier. In the outer tier, the airlines are responsible for modifying flight trajectories to mitigate the constraints identified by the traffic flow managers, before any flow plan is needed. In the middle tier, the traffic flow managers collaborate with the airlines to select and impose a flow plan, while the airlines continue to modify trajectories according to the flow plan. In the inner tier, the flow managers take over responsibility for modifying flight trajectories while incorporating airline preferences for flights, reroutes, and delay. The task analysis describes the activities in each tier to the level required for identifying the communication and information sharing between the airlines and the traffic flow managers. It also identifies benefit mechanisms and feasibility issues. Some key benefits mechanisms include reducing the traffic flow manager workload by shifting some responsibilities to airlines and increasing airline satisfaction by increasing their proactive participation and incorporating their preferences. Some key feasibility issues identified include the ability to delegate responsibility for flight trajectory changes to airlines and to coordinate among them. Addressing these issues avoids creating constraints elsewhere and ensures equity. Implications of the task analysis on future research related to feasibility and benefit assessments of the concept are discussed.

TIME-BASED CONFLICT RESOLUTION ALGORITHM AND APPLICATION TO DESCENT CONFLICTS

A time-based conflict resolution algorithm was developed to resolve predicted conflicts by time shifting (delaying or advancing) one of the flights prior to conflict. This resolution approach was applied to conflicts in the complex transition phase (from Center to Terminal airspace) involving flights that are also impacted by descent and time restrictions. In order to accurately account for the complex descent dynamics, a high fidelity trajectory model was used to analyze descent trajectories and the geometry of conflicts that occur in the descent phase of flight. The development of an accurate and efficient conflict resolution solution needed an accurate and simple analytical approximation of the descent trajectory. Therefore, linear and quadratic approximations of the trajectory model were assessed for their accuracy and ease of use in the conflict resolution algorithm. The quadratic approximation resulting in an average error of 0.05 nautical miles was more accurate than the linear approximation with an average error of 0.8 nautical miles. However, the linear approximation resulted in a simpler, and therefore more computationally efficient, closed form solution for the minimum time shift required for conflict resolution. It was shown that the time shift computed using the closed-form based on the linear approximation was extremely close to the more accurate time shift computed numerically based on the quadratic approximation. The difference was within 1 second (corresponding to about 0.1 nautical miles) for a relative course angle range between 30 and 150 degrees and under different descent speed profiles. The deviation increased marginally as the conflict occurred closer to the bottom of descent but the increase due to the conflict altitude was negligible. The conflict resolution algorithm and its analysis were applied to conflicts with a number of simplifying assumptions. Namely, the resolution is achieved by maintaining conservatively the horizontal separation requirement between an intruder aircraft with constant altitude and constant ground speed and a descending maneuver

Benefit Mechanisms of Enhanced Collaboration in Tactical Traffic Flow Management

*† ‡ § ** †† This study qualitatively identified the benefit mechanisms of an operational concept for enhanced collaboration in traffic flow management. The operational concept applies to the management of traffic within the airspace controlled by the Traffic Management Unit of an Air Route Traffic Control Center. The operational concept enhances the collaboration between traffic managers and airspace users (such as airlines) for mitigating the impact of local constraints such as convective weather, Special Use Airspace activity, and airspace congestion, and for facilitating user-preferred arrival metering. It is limited to a tactical time horizon up to two hours. A formal approach for the derivation and presentation of benefit mechanisms was followed. It ensures a consistent and comprehensive analysis and provides a visualization and communication tool that guides further research and development of the concept of operation. The approach maps key functions of the operational concept to technical benefits, and then to economic benefits, through causal links which constitute benefit mechanisms. Key operational elements that enable the benefit mechanisms and affect the resulting benefits value were also identified. This preliminary analysis forms the basis for future quantitative benefits assessments, which involve modeling the benefit mechanisms and associated operational elements presented in this paper.

Airline and Service Provider Collaborative Algorithms for Flight Route and Delay Decisions

In this paper, algorithms are presented that model increased collaboration between the air traffic service provider and airspace users on flight route and delay decisions. These decisions are part of the traffic flow management function that constrains demand below capacity. Currently, users cannot make changes to the route or delay of a flight close to or after departure time and instead must send requests to the service provider who attempts to accommodate the users based on congestion and workload limitations. To mitigate this limitation, the algorithms model a new collaboration scheme. First, users directly implement their flight route and delay decisions, when the flight is further from the congested airspace, without sending a request to the service provider. The service provider can override their action when the flight becomes closer to the congested airspace. Second, users send flight ranking, route ranking and location-to-absorb-delay preferences to the service provider. The service provider may reject these preferences if needed. The algorithms are used to study whether increasing users’ responsibility and increasing their preferences would prevent maintaining demand below capacity. To prevent demand from exceeding capacity the algorithms impose limits, such as available routes and imposed flow rates, on user decisions. A simulation case demonstrates the impact of the collaboration schemes on reducing demand below capacity within an en-route center. Preliminary results indicate that aircraft delay and, to a larger extent, passenger delay are reduced. However, congestion is reduced by a smaller amount when user preferences are considered by the service provider. Giving users responsibility according to service provider limits and delay feedback did not increase congestion.

Ground Automation Impact on Enabling Continuous Descent in High Density Operations

Continuous descent procedures provide reduced fuel costs and environmental benefits over traditional approaches with multiple level -altitude segments. However, they are difficult to implement in high traffic density environments since it is hard for a human controller to merge and space descending traffic without procedural level segments. Thus, introducing continuous descent in such environments may lead to disadvantages such as reducing the ability of the controller to predict aircraft trajectories, increasing controller workload and increasing the probability of loss of separation. In order to compensate, continuous descent procedures may require larger separation margins to avoid s eparation losses, resulting in reduced throughput. One approach to enable continuous descent approaches in high density operations is the use of ground -based automation to reduce the workload of air traffic controllers by providing assistance with key fun ctions such as separation assurance and flow constraint conformance. A preliminary evaluation of the effect of ground automation on the success of continuous descent in a high density environment is presented. For comparison, a baseline case models current human controller procedures (based on feedback from subject matter experts) in merging and spacing traffic in a situation where demand exceeds capacity and aircraft are assigned scheduled times of arrival at a meter fix. The baseline is compared to a hum an controller assisted with various levels of ground automation which may provide speed and path stretch advisories to assist the controller in meeting the scheduled times of arrival as well as conflict detectio n advisories. The magnitude of demand exceeding capacity is varied to investigate the sensitivity of the benefit provided by the ground automation to such factors. The benefit of the ground automation is quantified through metrics including continuous descent success rate and throughput at the meter fix.