Kapil Sheth

Aggregate Flow Model for Air-Traffic Management

Traditionally, models used in air-traffic control and flow management are based on simulating the trajectories of individual aircraft. This approach results in models with a large number of states, which are intrinsically susceptible to errors and difficult for designing and implementing optimal strategies for traffic flow management. This paper outlines an innovative approach for the development of linear-time-variant dynamic traffic flow system models based on historical data about the behavior of air traffic. The resulting low-order, linear, robust models can be used both for the analysis and synthesis of traffic flow management techniques for current and future systems.

Initial Study of Tube Networks for Flexible Airspace Utilization

Air traffic in the United States is reaching new highs as it continues to increase at a steady pace. There is a general consensus that the National Airspace System needs to be transformed from today’s rigid airways and airspace structure to a more flexible arrangement in order to accommodate and manage this growth. It has been suggested that one way to support this divergent growth in the mix of air traffic is to divide the airspace into different categories with different levels of service and entry requirements based on policy or price; e.g., connect high-traffic regions with a network of dedicated “tubes” analogous to the interstate highway system. This paper starts with today’s air traffic as a baseline, groups airports into regions, and models a series of tubes connecting major regions. We achieve this grouping in two different ways, and present results based on the two methods. Next, we present simulation results by connecting these regions with a network of tubes. The modeling approach provides a basis for systematically studying the design and impact of dynamic airspace concepts in the National Airspace System.

Performance evaluation of airborne separation assurance for free flight

Airborne separation assurance is a key requirement for free flight operations. This paper investigates the feasibility of airborne separation assurance for free flight by evaluating the performance of Conflict Detection and Resolution (CD&R) schemes in a simulated air traffic environment. Two qualitatively different CD&R methods were evaluated in an air traffic simulation environment provided by the Future ATM Concepts Evaluation Tool (FACET). The evaluation was based on a horizontal-plane free flight traffic scenario constructed with initial conditions from actual air traffic data; nearly a thousand aircraft were modeled in this 6-hour scenario. The results of the performance evaluation indicate that airborne separation assurance performed quite well in the free flight evaluations: (1) All of the conflicts were resolved; (2) The impact on flight efficiency, as measured by path-length and flight-time changes, was quite small; and, (3) The impact on system stability, as measured by additional aircraft experiencing conflicts due to the “domino effect,” was modest.

Migration of FACET from simulation environment to dispatcher decision support system

This paper describes the approach taken to develop AOC requirements, assess the feasibility of implementing the requirements and ongoing efforts to transfer FACET-derived technology to users of the NAS. The advances made in the state of the art for handling of flights using integrated air traffic and weather data, along with the coupled applications of risk analysis, demand forecasting and management, and efficient route planning for various phases of flight are addressed. Although implementation issues are presented here with respect to FACET, the comments apply generally to the development of most dispatcher tools.

Incorporating User Preferences in Collaborative Traffic Flow Management

This paper presents a preferred route selection method that includes a concept of credit points for improving collaboration between participants in Traffic Flow Management. The notion of expending credit points by users to prioritize their flights is considered for selecting alternate flight routes. Starting with a simple scenario containing a few flights, the paper presents four route selection modes for each flight, a sequential approach and aggressive, moderate and conservative user behaviors. Flights were simulated based on selected routes, with an automated system monitoring airspace constraints. With the current fidelity of the experiments, adopting a moderate or conservative approach appears to provide more benefit than being an aggressive user when all flights depart at the same time. Additionally, two different traffic scenario data (current and three times the current traffic) were used in the dynamic case to assess the utility of such a concept with timevarying schedules. Results indicate that the current implementation with moderate user behavior handles these traffic scenarios in a reasonable time and satisfies the airspace constraints.

Analysis of airspace tube structures

This paper presents analysis of five airspace tube structures; three of which were previously defined and two new designs that were generated for this research. Five metrics to characterize the performance of these tubes are described. The metrics address the spatio-temporal utilization, frequency and angles at which aircraft cross tubes, along with separation of aircraft with and without tubes. All of the designs were incorporated in a common simulation platform for evaluation. The results indicate that current designs of tubes have low utilization and improvements are needed for additional benefits. Other structural parameters for consideration in future designs are presented along with visualization of a simple three-dimensional tube network.

Application of Probabilistic Convective Weather Forecasts for Flight Routing Decisions

An available probabilistic convective weather predicts probabilities of severe weather occurrence in the continental United States up to a six-hour period. This paper examines the forecast for making flight routing decisions. By synchronizing the forecast with air traffic data in a simulation, the intensity and ceilings of the forecasted weather are used to derive a cut-off probability value, which represents the bounding probability contour that aircraft are most likely to avoid. This parameter is an important metric for meteorologists in improving the accuracy of weather forecasts from an air traffic management perspective. The cut-off parameter for this forecast product was computed as 35% for a one-hour forecast, over a three-month period during summer of 2007. The results are shown for different altitude levels, aircraft types and airspace users. Using this parameter, a method of calculating flight distances and times, while avoiding specific areas of convective activity is presented for flight planning decisions. Several improvements to the forecast weather data, such as frequency, accuracy, and coverage, are suggested to improve the utility of weather data in air traffic management. I. Introduction LIGHT delays in the United States have been steadily increasing with the increase in air traffic. The Federal Aviation Administration’s (FAA) Operational Network (OPSNET) data show that during the two four-month periods from May through August of 2005 and 2006, weather related delays accounted for about 70% of all reported delays. The current deterministic weather prediction in tactical (within the next 2 hours) timeframe is at a manageable level of accuracy; however, the state of weather forecasting for strategic (2-6 hours) time frame needs improvement for longer-term flight planning. 1 In the absence of weather forecasts with sufficient accuracy, the decision-making for flights longer than two hours is challenging. The Joint Planning and Development Office working on Next Generation (NextGen) Air Transportation System considers weather-assimilated decision-making a principal area of research. The NextGen Weather Integrated Product Team has considered integrated weather information and improved aviation weather forecasts as two of the main efforts for future development.

Network Characteristics of Air Traffic in the Continental United States

Abstract Air traffic is undergoing big changes both in developed and developing countries. The demand for air traffic in the United States is expected to grow to 2 or 3 times the current levels of traffic in the next few decades. This paper models demand for air traffic as a network with several thousand nodes. Recently, methods have been developed to study the network characteristics of large complex systems in many natural and engineering fields. Several networks exhibit the “scale-free” property that as the network grows in size, a small number of components have a disproportionate influence on the successful operation of the network. This paper describes the network properties of the current air traffic system and uses future scenarios of air traffic growth to understand the performance of future air traffic networks. The air traffic network exhibits an exponentially truncated scale-free behavior. It is shown that a three-times growth in the overall traffic may result in a ten-times impact on the density of traffic in certain parts of the United States. Thus, in addition to bottlenecks at major airports, the risk of en route traffic saturation calls for route restructuring and the introduction of new operational concepts, such as automation to increase en route capacity.

Simulations of Credits Concept with User Input for Collaborative Air Traffic Management

This paper describes the procedure and outcome of a human-in-the-loop simulation experiment. The purpose of the simulation was to study feasibility of incorporating user flight preferences in air traffic demand and capacity management. Five airline dispatchers specified flight priorities for multiple routes. These priorities were used for airspace constraint management by creating a new credit ranked flight departure schedule. One air traffic manager prescribed and managed the airspace constraints. The dispatchers were trained on the system using different traffic scenarios. A realistic data set with convective weather was used for generating final results. Based on the experiment results, the credits concept allowed users to prioritize their flights and to distribute delays as per their preference. It was also observed that the delays could be reduced and better distributed among users with respect to a first-come-first served schedule, without violating airspace constraints. The study elicited several factors for prioritizing flights from the users’ perspective, which could be used in future fast-time simulations.

Enhancing Collaboration in Air Traffic Flow Management

This paper extends the concept of credit points to enhance collaboration between participants in air traffic flow management. In earlier research, a preferred route selection method was presented, where users expend credit points to prioritize the flight paths for each of their pre-departure flights. This method of prioritizing flights provides a mechanism to incorporate users’ preferences in air traffic management subject to airspace congestion and weather impact constraints. In the current research, the airport arrival and departure rates at the top 70 airports are incorporated. In order to analyze the equity of arrival and departure schedules, the flight distributions at those airports were constructed for the 40 largest flight operators in the United States. The credit-points concept gives airborne flights the highest priority, enabling them to better maintain their schedule. A negotiation mechanism for participants to reassess their decisions for improved operations is described. Results for violations of arrival/departure rates and airspace constraints (due to volume and weather) before and after implementing the concept, along with credit use and incurred delays are presented. Results indicate that the credit-points concept is feasible for users to incorporate their preferences of important flights. The overall delay compared to a schedule based system reduces while maintaining airspace and airport capacities. Also, the equity increases for participating users as more constraints are added due to better utilization of available airspace.