A Review of Conflict Detection and Resolution Modeling Methods
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paper_title: Design of a conflict detection algorithm for the Center/TRACON automation system

paper_content:

An algorithm for detecting and analyzing potential enroute conflicts has been designed and implemented within the Center-TRACON Automation System (CTAS). The design uses the 4D trajectories provided by CTAS to produce a set of probable future conflicts, and assists the enroute sector controller in efficiently resolving these conflicts. Conflicts are detected via comparisons of trajectories at closely spaced time instants, with measures taken to limit the computations required to complete the search. Performance tests indicate more than 800 aircraft can be processed by the conflict detection and analysis algorithm within a search cycle of 10 seconds. This suggests that the search algorithm easily meets the performance requirements for an automated conflict detection and resolution tool in the current air traffic system. The algorithm includes a trial resolution functionality which automatically detects conflicts of proposed resolutions, and gives near instantaneous feedback to controller input. Field evaluation of the Conflict Probe will be conducted at the Denver and Fort Worth Air Route Traffic Control Centers (ARTCC) beginning in September, 1997.
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paper_title: Conflict detection and alerting for separation assurance systems

paper_content:

Many of the nation's airspace users desire an increase in efficiency in the air traffic control system. Some feel that an increase in efficiency can be achieved by moving away from a centralized control paradigm towards a distributed control paradigm. In a distributed control paradigm, the cockpit crew would have more freedom in selecting and modifying their routes. This new paradigm is part of the Free Flight concept. Increased autonomy of operations will require increases in cockpit information, pilot responsibility, and avionics capability. One of the key enabling capabilities will be the detection and resolution of air traffic conflicts. CDR a baseline conflict detection algorithm based on instantaneous state vectors; and an analysis of the algorithm's performance for flight data from the ADS-B Operational Evaluation.
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paper_title: Assessment of field trials, algorithmic performance, and benefits of the User Request Evaluation Tool (URET) conflict probe

paper_content:

In order to respond to rising demands for services from the National Airspace System (NAS), the Federal Aviation Administration (FAA) and The Mitre Corporation's Center for Advanced Aviation System Development (CAASD) have developed and evaluated a set of en route air traffic control (ATC) decision support capabilities based on many of years of earlier work on the Advanced En Route ATC (AERA) program. The component capabilities-embodied in a prototype referred to as the User Request Evaluation Tool (URET)-include a conflict probe that continuously checks current flight plan trajectories for strategic conflicts, and a Trial Planning function that allows a controller to expeditiously evaluate problem resolutions before they are issued as clearances. These capabilities are intended to provide the flexibility and decision support needed to allow more user preferences to be met while continuing to maintain or enhance today's level of safety. The URET prototype was deployed to the Indianapolis Air Route Traffic Control Center (ARTCC) for field trials in January 1996 and later expanded to include more sectors and to span longer periods of time. In addition, the prototype has been deployed and is being evaluated at the Memphis ARTCC. This paper presents key findings from the field trials and from other related activities.
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paper_title: KNOWLEDGE-BASED COLLISION AVOIDANCE

paper_content:

This paper describes preliminary studies towards a navigational Knowledge-based System currently in progress within the School of Engineering and Technology Management at Liverpool Polytechnic
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paper_title: Obstacle Avoidance in a Dynamic Environment: A Collision Cone Approach

paper_content:

A novel collision cone approach is proposed as an aid to collision detection and avoidance between irregularly shaped moving objects with unknown trajectories. It is shown that the collision cone can be effectively used to determine whether collision between a robot and an obstacle (both moving in a dynamic environment) is imminent. No restrictions are placed on the shapes of either the robot or the obstacle, i.e., they can both be of any arbitrary shape. The collision cone concept is developed in a phased manner starting from existing analytical results that enable prediction of collision between two moving point objects. These results are extended to predict collision between a point and a circular object, between a point and an irregularly shaped object, between two circular objects, and finally between two irregularly shaped objects. Using the collision cone approach, several strategies that the robot can follow in order to avoid collision, are presented. A discussion on how the shapes of the robot and obstacles can be approximated in order to reduce computational burden is also presented. A number of examples are given to illustrate both collision prediction and avoidance strategies of the robot.
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paper_title: A Dynamic Conflict Probe and Index of Collision Risk

paper_content:

We present a mathematical index of colllision risk and propose it as a candidate conflict probe for use in free flight. The index can be used to aid and measure ATC and pilot performance during simulated or real flight. The instantaneous value of the index is a relative (ordinal) measure of global situational risk. When the value of the index is graphed over time, conflicts can be easily identified and their severity estimated. Peak values indicate approximate times and degree of risk associated with the minimum separation of aircraft.
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paper_title: Collision avoidance as a differential game: real-time approximation of optimal strategies using higher derivatives of the value function

paper_content:

Contemporary developments of on-board systems for automatic or semi-automatic driving include car collision avoidance. For this purpose a worst case approach based on pursuit-evasion differential games is investigated. On a freeway a correct driver (evader) is faced with a wrong driver (pursuer) ahead. The correct driver tries to avoid a collision against all possible wrong driver's maneuvers and additionally tries to stay on the freeway. The representation of an optimal collision avoidance strategy along a lot of optimal paths is used to synthesize a collision avoidance strategy globally by means of Taylor series expansions of the value function's gradient. Examples of simulations which proved satisfactory performance of the on-board collision avoidance system against various typical maneuvers of wrong drivers are presented.
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paper_title: Design of a conflict detection algorithm for the Center/TRACON automation system

paper_content:

An algorithm for detecting and analyzing potential enroute conflicts has been designed and implemented within the Center-TRACON Automation System (CTAS). The design uses the 4D trajectories provided by CTAS to produce a set of probable future conflicts, and assists the enroute sector controller in efficiently resolving these conflicts. Conflicts are detected via comparisons of trajectories at closely spaced time instants, with measures taken to limit the computations required to complete the search. Performance tests indicate more than 800 aircraft can be processed by the conflict detection and analysis algorithm within a search cycle of 10 seconds. This suggests that the search algorithm easily meets the performance requirements for an automated conflict detection and resolution tool in the current air traffic system. The algorithm includes a trial resolution functionality which automatically detects conflicts of proposed resolutions, and gives near instantaneous feedback to controller input. Field evaluation of the Conflict Probe will be conducted at the Denver and Fort Worth Air Route Traffic Control Centers (ARTCC) beginning in September, 1997.
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paper_title: Assessment of field trials, algorithmic performance, and benefits of the User Request Evaluation Tool (URET) conflict probe

paper_content:

In order to respond to rising demands for services from the National Airspace System (NAS), the Federal Aviation Administration (FAA) and The Mitre Corporation's Center for Advanced Aviation System Development (CAASD) have developed and evaluated a set of en route air traffic control (ATC) decision support capabilities based on many of years of earlier work on the Advanced En Route ATC (AERA) program. The component capabilities-embodied in a prototype referred to as the User Request Evaluation Tool (URET)-include a conflict probe that continuously checks current flight plan trajectories for strategic conflicts, and a Trial Planning function that allows a controller to expeditiously evaluate problem resolutions before they are issued as clearances. These capabilities are intended to provide the flexibility and decision support needed to allow more user preferences to be met while continuing to maintain or enhance today's level of safety. The URET prototype was deployed to the Indianapolis Air Route Traffic Control Center (ARTCC) for field trials in January 1996 and later expanded to include more sectors and to span longer periods of time. In addition, the prototype has been deployed and is being evaluated at the Memphis ARTCC. This paper presents key findings from the field trials and from other related activities.
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paper_title: Pilot non-conformance to alerting system commands during closely spaced parallel approaches

paper_content:

Pilot non-conformance to alerting system commands has been noted in general and to a TCAS-like collision avoidance system in a previous experiment. This paper details two experiments studying collision avoidance during closely-spaced parallel approaches in IMC, and specifically examining possible causal factors of, and design solutions to, pilot non-conformance.
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paper_title: Probability-based collision alerting logic for closely-spaced parallel approach

paper_content:

A prototype airborne collision alerting logic was developed for aircraft on approach to closely-spaced parallel runways. A novel design methodology was used based on collision probabilities instead of traditional spatial or temporal alerting criteria. With this technique, an alert is issued when the probability of a collision exceeds an acceptable threshold value. The logic was based on a hazard level corresponding to the current Precision Runway Monitor System of one accident in every one thousand worst-case blunders. Probability contours were constructed through Monte Carlo simulation over a range of aircraft position, speed, heading, and turn rate conditions. These contours were stored in look-up tables that were accessed in real time for evaluation during numerical simulation of approaches. Three runway spacings were investigated: 3,400, 2,500, and 1,700 ft. The results show that the unnecessary alert rate at 1,700 ft runway spacing was double that at 3,400 ft runway spacing. Additionally, the logic induced collisions in two low-closure-rate situations, suggesting that the worst case blunder may not be a drastic heading change. (Author)
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paper_title: Design of cockpit displays for limited delegation of separation assurance

paper_content:

The Evolutionary Air-ground Co-operative ATM Concepts (EACAC) study of the FREER-FLIGHT project investigates the delegation, by the controller to the pilot, of some tasks related to separation assurance. Starting from the analogy of visual clearances, EACAC investigates the possibility of giving electronic clearances in managed airspace. One of the issues of the study deals with the appropriate assistance scheme to be provided to the pilot, considering the proposed concept of limited delegation. An initial design work has been done, leading to the definition of key elements for cockpit displays: three different levels of assistance are identified, with different representations. All these options will be evaluated by pilots, first through a cockpit environment in a stand-alone mode (end 1999), and then using a cockpit simulator in a real-time simulation with controllers (mid 2000).
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paper_title: Conflict Resolution Advisory Service in autonomous aircraft operations

paper_content:

Recent advances in air traffic Communication Navigation and Surveillance (CNS) have encouraged investigations into the concept following which Air Traffic Control functions can be delegated to the flight deck, allowing more freedom of movement to airspace users. In late 1995, an initiative, known under the project name FREER, for Free-Route Experimental Encounter Resolution, was introduced at EUROCONTROL to investigate the feasibility of this concept. In this paper, we present the initial results obtained from the Autonomous Aircraft Operations study (FREER-I) that targets full delegation of ATC to aircraft operating in low-density airspace. Specific issues of Autonomous Aircraft Operations (AAO) supporting free-route, free flight and user-preferred routing are discussed. A description of the current prototype illustrating the Airborne Interactive Conflict Resolution Advisory service is included.
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paper_title: Medium term conflict detection in EATCHIP phase III

paper_content:

The European ATC Harmonization and Integration Programme, EATCHIP, is a phased programme, where phases I and II dealt with assessment of the current situation and setting goals for the programme run by the EUROCONTROL Agency on behalf of the 35 Member States of the European Civil Aviation Conference. EATCHIP Phase III is the first harmonized acquisition and implementation phase. EATCHIP Phase IV will include very advanced ATM automation up to the year 2015 (and beyond). This paper gives background information on detection of conflicts in EATCHIP Phase III timeframe in Europe and a brief description of capabilities of the EATCHIP Phase III Medium Term Conflict Detection tool.
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paper_title: Design of a conflict detection algorithm for the Center/TRACON automation system

paper_content:

An algorithm for detecting and analyzing potential enroute conflicts has been designed and implemented within the Center-TRACON Automation System (CTAS). The design uses the 4D trajectories provided by CTAS to produce a set of probable future conflicts, and assists the enroute sector controller in efficiently resolving these conflicts. Conflicts are detected via comparisons of trajectories at closely spaced time instants, with measures taken to limit the computations required to complete the search. Performance tests indicate more than 800 aircraft can be processed by the conflict detection and analysis algorithm within a search cycle of 10 seconds. This suggests that the search algorithm easily meets the performance requirements for an automated conflict detection and resolution tool in the current air traffic system. The algorithm includes a trial resolution functionality which automatically detects conflicts of proposed resolutions, and gives near instantaneous feedback to controller input. Field evaluation of the Conflict Probe will be conducted at the Denver and Fort Worth Air Route Traffic Control Centers (ARTCC) beginning in September, 1997.
---
paper_title: Assessment of field trials, algorithmic performance, and benefits of the User Request Evaluation Tool (URET) conflict probe

paper_content:

In order to respond to rising demands for services from the National Airspace System (NAS), the Federal Aviation Administration (FAA) and The Mitre Corporation's Center for Advanced Aviation System Development (CAASD) have developed and evaluated a set of en route air traffic control (ATC) decision support capabilities based on many of years of earlier work on the Advanced En Route ATC (AERA) program. The component capabilities-embodied in a prototype referred to as the User Request Evaluation Tool (URET)-include a conflict probe that continuously checks current flight plan trajectories for strategic conflicts, and a Trial Planning function that allows a controller to expeditiously evaluate problem resolutions before they are issued as clearances. These capabilities are intended to provide the flexibility and decision support needed to allow more user preferences to be met while continuing to maintain or enhance today's level of safety. The URET prototype was deployed to the Indianapolis Air Route Traffic Control Center (ARTCC) for field trials in January 1996 and later expanded to include more sectors and to span longer periods of time. In addition, the prototype has been deployed and is being evaluated at the Memphis ARTCC. This paper presents key findings from the field trials and from other related activities.
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paper_title: USING INTENT INFORMATION IN PROBABILISTIC CONFLICT ANALYSIS

paper_content:

A method to incorporate aircraft flight path intent information into a conflict detection and resolution system is described. The approach uses a set of probability density functions that describe potential trajectory errors such as cross-track, along-track, or course change, in a series of Monte Carlo simulations. The simulations are used to estimate the probability of conflict in traffic encounters. Intent information is readily included in the model, and can consist of a series of waypoints, heading or track holds, target altitudes, or maneuvering limitations from free flight concepts. The method also allows for direct incorporation of the confidence with which an intended path will be followed. An efficient modeling method is used that enables the Monte Carlo simulations to be run in real time, suggesting that such an approach could be used in conflict detection systems. Several example traffic encounters are discussed using conflict probability maps that show regions in which a conflict will likely occur. The potential benefit of access to intent information in a vertical conflict example is also shown.
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paper_title: Computationally efficient conflict detection methods for air traffic management

paper_content:

Air Traffic Management (ATM) combines the roles of Air Traffic Control (ATC) and Traffic Flow Management (TFM). Generally, TFhl is concerned with the smooth and efficient flow of traffic in the airspace while ATC has the responsibility for maintaining the separation between aircraft. The challenge for the ATM system is to accommodate growth in air traffic while maintaining the same level of safety and increased operator flexibility. This can only be achieved by introducing the technological innovations in Communication, Navigation and Surveillance (CNS) and by the development of decision support tools for controllers, pilots and airline operations. Basic components of these decision support tools are algorithms and software for conflict detection and resolution. This paper takes a detailed look at the standard approach to conflict detection in order to reduce the number of computations. The number of computations are reduced by posing the conflict detection problem in two steps: (a) spatial separation and (b) temporal separation. Three algorithms for conflict detection are described. The first method describes the standard approach. It computes the Euclidean distance between all aircraft pairs and compares the distance to the allowable minimum separation distance. The number of computations required by this method are of the order of n2 where n is the number of aircraft. The second algorithm transforms the planned trajectories of the aircraft into a sequence of discrete spatial regions which are then sorted to locate regions in airspace where conflict is possible. The number of computations in this case are of the order of nlog, n. The third algorithm uses an accumulator driven by the transformed trajectories to locate regions where conflict is possible. It is shown that the computational complexity of this algorithm is of the order of n. Algorithmic details of the sorting-based and accumulator-based algorithms are provided. Numerical examples are presented to demonstrate the theoretical computational advantage of using the sorting-based and accumulator-based conflict detection algorithms over the standard method.
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paper_title: Comparison of Centralized and Decentralized Conflict Resolution Strategies for Multiple-Aircraft Problems

paper_content:

Under the concept of Free Flight, future air traffic operations may permit the transfer of responsibility for various tasks, including conflict detection and resolution, from ground-based air traffic controllers to the flight crew. While aircraft-based conflict resolution is attractive from a user-preferences standpoint, the degree to which it can efficiently resolve complex conflicts among several interacting aircraft remains a significant issue. The objective of this study is to compare the performance of a decentralized conflict resolution strategy against that of a benchmark centralized conflict resolution strategy. A generalized methodology for such a comparison does not exist; therefore two qualitatively different conflict scenarios, characterized by complex interactions among multiple aircraft, were constructed to conduct simulation studies using an idealized model. Preliminary investigations indicate that a decentralized resolution strategy can successfully solve complex multiple-aircraft problems in real time, albeit with some performance degradation relative to a centralized strategy. Research Scientist, Automation Concepts Research Branch; Mail Stop 210-10; E-mail; kbilimoria@mail.arc.nasa.gov. Associate Fellow, AIAA. f Software Specialist, Raytheon ITSS. Research Assistant, Dept. of Aeronautics and Astronautics. Associate Professor, Dept. of Aeronautics and Astronautics; E-mail: feron@mit.edu. Senior Member, AIAA. Copyright © 2000 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes. All other rights are reserved by the copyright owner. Introduction The advent of new technologies for Air Traffic Management (ATM) has the potential to change the operational paradigm of the air transportation system by delegating more responsibility to the flight deck for airplane trajectory management functions; this includes conflict detection and resolution (CDR this is an idealized representation of a situation where several "free flying" aircraft are simultaneously attempting to arrive at some terminal area entry point. The second scenario features two closelyspaced traffic streams (each consisting of several aircraft) intersecting at a common point; this is an idealized representation of aircraft flying along intersecting "free routes" in en route airspace. The performance of a reactive decentralized resolution method that provides sequential, pairwise conflict resolutions based on a geometric optimization approach10 is compared against that of a proactive centralized resolution method that provides a single coordinated conflict resolution based on a global optimization algorithm.5 Although determining a fully coordinated optimal solution to conflicts involving multiple aircraft is computationally challenging, the centralized conflict resolution method described in Ref. 5 is able to compute these solutions, which are used as benchmarks for the best performance that can be achieved. The performance of decentralized strategies is then compared against these benchmark solutions. This paper is organized as follows: First, the mathematical models used for aircraft trajectories and conflict avoidance are presented. The centralized and decentralized conflict resolution methods used in this study are then outlined. Next, performance measures for conflict resolution are defined, and two conflict scenarios are described. Finally, a comparison of the performance of the decentralized conflict resolution strategy relative to the centralized conflict resolution strategy is presented, along with some general observations about their characteristics.
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paper_title: Deterministic resolution of two aircraft conflict in free flight

paper_content:

This paper studies strategies for resolving two aircraft conflicts in a free flight environment for air traffic management. In a free flight environment, pilots of individual aircraft can change flight paths in real time. As a result, resolving conflicts among aircraft becomes a key priority for controllers. In this paper, a pointmass level flight aircraft model is used. Resolution of a two-aircraft conflict is formulated as deterministic nonlinear optimal control problems. Performance indices are selected to minimize deviations of both aircraft from their originally-intended flight paths or to minimize banking angles, subject to a minimum separation requirement. In addition, terminal constraints are included that force each aircraft to return to its original path after conflict avoidance maneuvers. In an unrestricted region, it is assumed that aircraft are originally flying with a constant heading. In general, the two aircraft would turn the same way (left or right) by roughly the same amount to avoid a conflict. When the intersecting angle is small, however, one aircraft needs to take a path stretching to avoid the other aircraft. In the terminal region where aircraft converge to the same gate, one aircraft needs to stretch its flight paths to avoid the other aircraft. If the two aircraft have the same speed, either aircraft can perform the path stretching. If the two aircraft have different speeds, the slower aircraft should perform the path stretching.
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paper_title: Conflict detection and alerting for separation assurance systems

paper_content:

Many of the nation's airspace users desire an increase in efficiency in the air traffic control system. Some feel that an increase in efficiency can be achieved by moving away from a centralized control paradigm towards a distributed control paradigm. In a distributed control paradigm, the cockpit crew would have more freedom in selecting and modifying their routes. This new paradigm is part of the Free Flight concept. Increased autonomy of operations will require increases in cockpit information, pilot responsibility, and avionics capability. One of the key enabling capabilities will be the detection and resolution of air traffic conflicts. CDR a baseline conflict detection algorithm based on instantaneous state vectors; and an analysis of the algorithm's performance for flight data from the ADS-B Operational Evaluation.
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paper_title: Conflict Detection and Resolution for Free Flight

paper_content:

Conflict detection and resolution has a long history of investigation, but further investigation is necessary as a result of new Free Flight policies removing many constraints; new data link, GPS, ...
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paper_title: AI knowledge model for self-organizing conflict prevention/resolution in close free-flight air space

paper_content:

An artificial intelligence (AI) knowledge model is proposed as a basis for automated conflict management in close free-flight air space. A conceptual framework of the model is developed. The problem of air traffic control (ATC) within a group of potentially conflicting vehicles is represented as an autonomous, self-organizing process. This process incorporates the principles of collective behavior observed in nature (bird flocking, fish schooling, insect swarming, etc.) and comprehensive knowledge of the "pilot vehicle-operational environment" system dynamics derived from special computer experiments. Through this process, real-time knowledge-based predictions of near term flight paths are made to prevent and resolve conflicts in a group of vehicles under normal and demanding conditions. The model may be useful for prototyping intelligent technologies for assisted and automatic collision avoidance in close air space.
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paper_title: Conflict Detection and Resolution for Future Air Transportation Management

paper_content:

With a Free Flight policy, the emphasis for air traffic control is shifting from active control to passive air traffic management with a policy of intervention by exception. Aircraft will be allowed to fly user preferred routes, as long as safety Alert Zones are not violated. If there is a potential conflict, two (or more) aircraft must be able to arrive at a solution for conflict resolution without controller intervention. Thus, decision aid tools are needed in Free Flight to detect and resolve conflicts, and several problems must be solved to develop such tools. In this report, we analyze and solve problems of proximity management, conflict detection, and conflict resolution under a Free Flight policy. For proximity management, we establish a system based on Delaunay Triangulations of aircraft at constant flight levels. Such a system provides a means for analyzing the neighbor relationships between aircraft and the nearby free space around air traffic which can be utilized later in conflict resolution. For conflict detection, we perform both 2-dimensional and 3-dimensional analyses based on the penetration of the Protected Airspace Zone. Both deterministic and non-deterministic analyses are performed. We investigate several types of conflict warnings including tactical warnings prior to penetrating the Protected Airspace Zone, methods based on the reachability overlap of both aircraft, and conflict probability maps to establish strategic Alert Zones around aircraft.
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paper_title: Rule Optimization for Airborne Aircraft Separation

paper_content:

An antenna and antenna coupling apparatus is provided in which a receiving antenna is used with a super regenerative transponder receiver. The antenna comprises a coaxial cable which has the outer conductor stripped away from the inner conductor at one end and both the outer conductor and inner conductor bent so as to be at right angles. At the other end of the cable the outer conductor is also stripped away from the inner conductor and both are also bent at right angles. The coaxial cable passes through a shield enclosing the receiver and is soldered at the center of the bottom of the shield thus coupling the antenna to the receiver.
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paper_title: KNOWLEDGE-BASED COLLISION AVOIDANCE

paper_content:

This paper describes preliminary studies towards a navigational Knowledge-based System currently in progress within the School of Engineering and Technology Management at Liverpool Polytechnic
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paper_title: AIRCRAFT COLLISION AVOIDANCE TRAJECTORY GENERATION

paper_content:

This paper presents a new approach to the aircraft collision avoidance problem. This approach gives a recommended avoidance trajectory in both the horizontal and vertical planes of motion based on the geometric relationship between aircraft and threats. A new concept, the "threat map", is introduced to describe moving threats as static threats. Thus, motion planning for dynamic threats is reduced to path planning for stationary threat avoidance. At every time interval, the threat map is updated and the velocity direction of the aircraft is calculated to avoid the threats. The "risk space" is used to model a threat By avoiding the risk space, the aircraft avoids the threat while keeping a safe separation. Some simulation studies show the effectiveness of the proposed approach.
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paper_title: Conflict Resolution for Air Traffic Management: a Study in Multi-Agent Hybrid Systems

paper_content:

Air Tra c Management (ATM) of the future allows for the possibility of free ight, in which aircraft choose their own optimal routes, altitude and speed. In a free ight environment, the trajectories of di erent aircraft may be con icting, in which case aircraft may or may not cooperate in resolving the con ict. In this paper, both cooperative and noncooperative con ict resolution methods are presented. Noncooperative methods are based on game theory in which each aircraft models the actions of other aircraft as disturbances and chooses its actions to be safe against the worst possible disturbance. The solutions to the games partition the state space into safe and unsafe sets and the control strategies are abstracted into discrete protocols on hybrid automata. In cooperative methods, aircraft perform coordinated maneuvers in order to avoid con ict. The merging of inter-aircraft coordination protocols with the individual continuous control laws of each aircraft gives rise to hybrid systems which have been made safe by design. Two examples of con ict resolution using speed and heading changes are worked out in detail.
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paper_title: Optimal Resolution of En Route Conflicts

paper_content:

Designing a Control Simulator involves many difficult problems: modeling conflict detection, trajectory uncertainties, solving conflict inside sectors, respecting military areas constraints, coordinating aircraft between sectors, etc\ldots Moreover, the n-aircraft conflict resolution problem is highly combinatorial and cannot be optimally solved using classical mathematical optimization techniques. The set of admissible solutions is made of many unconnected subsets enclosing different local optima, but the subset enclosing the optimum cannot be found a priori. In this paper, we present a conflict solver and its implementation in an Air Traffic simulator, with statistical results on real traffic in a French Sector. This solver, which takes into account real flight plans, solves every conflict inside a sector or over the French airspace on a loaded day.
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paper_title: Obstacle Avoidance in a Dynamic Environment: A Collision Cone Approach

paper_content:

A novel collision cone approach is proposed as an aid to collision detection and avoidance between irregularly shaped moving objects with unknown trajectories. It is shown that the collision cone can be effectively used to determine whether collision between a robot and an obstacle (both moving in a dynamic environment) is imminent. No restrictions are placed on the shapes of either the robot or the obstacle, i.e., they can both be of any arbitrary shape. The collision cone concept is developed in a phased manner starting from existing analytical results that enable prediction of collision between two moving point objects. These results are extended to predict collision between a point and a circular object, between a point and an irregularly shaped object, between two circular objects, and finally between two irregularly shaped objects. Using the collision cone approach, several strategies that the robot can follow in order to avoid collision, are presented. A discussion on how the shapes of the robot and obstacles can be approximated in order to reduce computational burden is also presented. A number of examples are given to illustrate both collision prediction and avoidance strategies of the robot.
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paper_title: Air traffic controller agent model for free flight

paper_content:

The objective of this research was to design and demonstrate an agent-based modeling and analysis tool for evaluating air traffic controller (ATC) performance under free flight air traffic management (ATM), and to develop a distributed decision-making model to investigate the potential for collaborative problemsolving under free flight. We developed a set of intelligent agent models representing ATC and pilot behavior in free flight. These models contain simplified representations of information processing and situation assessment applied to air traffic conflict detection. They also contain detailed air traffic conflict resolution models applying collaborative decisionmaking via inter-agent negotiation. We demonstrated the operation of a limited-scope prototype in a set of simulation trials designed to exercise the multi-agent decision-making model under a spectrum of free flight air traffic configurations. The results showed that our agent models are capable of performing on-line learning to support global situation awareness (SA) in the air traffic environment. The nature of conflict resolution maneuvers negotiated by the agents varied with conflict geometry in a manner consistent with intuitive expectation.
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paper_title: Stream Option Manager (SOM): automated integration of aircraft separation, merging, stream management, and other air traffic control functions

paper_content:

Stream Option Manager (SOM) is a proposed concept for automated integration of aircraft separation, merging and stream management, using linear programming techniques. It was developed as part of a research and development initiative for air traffic control (ATC) automation concepts, sponsored by the Federal Aviation Administration (FAA) and performed by MITRE Corporation. SOM is research; it has not been approved by the FAA for use in future ATC. SOM's purpose is to resolve possible problems involving multiple aircraft with given flight paths. Each aircraft must be separated by a minimum distance from every other aircraft at all times, and certain sets of aircraft (e.g., those about to land at a particular airport) must be merged or metered (lined up, or separated in trail by a given distance). Aircraft in sets called streams must be separated in the along-route direction at all times. Each aircraft is also subject to certain speed limits. Given the pilot-preferred flight paths, and separation, metering, stream, and speed requirements, SOM finds modified flight paths for each aircraft that satisfy all the requirements yet stay as close as possible to the pilot-preferred paths. SOM's algorithm represents the (x, y, z) positions of each aircraft at future times as variables in a linear program. The requirements are expressed or approximated by linear inequalities or equalities. Pilot preferences are approximated by a linear objective function. The SOM algorithm has been implemented successfully in a prototype simulation in 2D. Scenarios with up to 15 aircraft and 24 separation and/or merging problems have been resolved. >
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paper_title: Maneuver option manager: automated simplification of complex air traffic control problems

paper_content:

Maneuver option manager (MOM) is part of an air traffic control automation project, sponsored by the Federal Aviation Administration (FAA), in which the computer for the first time assumes responsibility for separation assurance between en route aircraft. MOM's purpose is to detect and simplify certain complex air traffic control problems, identified here as sets of interrelated potential pairwise separation problems. MOM determines which of six types of maneuver options is available (free of possible separation problems) for each aircraft. MOM simplifies a complex problem by protecting (for future use) an available maneuver option for one or more of the involved aircraft. Routinely, a single maneuver option resolves multiple pairwise problems. MOM's actions cause complex problems to be iteratively broken down into independent, smaller, and less complex problems. >
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paper_title: Optimal Strategies for Free Flight Air Traffic Conflict Resolution

paper_content:

Recent advances in navigation and data communication technologies make it feasible for individual aircraft to plan and fly their trajectories in the presence of other aircraft in the airspace. This way, individual aircraft can take advantage of the atmospheric and traffic conditions to optimally plan their paths. This capability is termed as the free flight concept. While the free flight concept provides new degrees of freedom to the aircraft operators, it also brings-in complexities not present in the current air traffic control system. In the free flight concept, each aircraft has the responsibility for navigating around other aircraft in the airspace. While this is not a difficult task under low speed, low traffic density conditions, the complexities of dealing with potential conflict with multiple aircraft can significantly increase the pilot’s work load. This paper presents the development of a conflict resolution algorithm based on the quasilinearization method to enable the practical implementation of the free flight concept. The algorithm development uses nonlinear point-mass aircraft models, and incorporates realistic operational constraints on individual aircraft. The analytical framework can also incorporate information about ambient atmospheric conditions. Realistic conflict resolution scenarios are illustrated. Due to their speed of execution, these conflict resolution algorithms are suitable for implementation on-board aircraft.
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paper_title: Free flight separation assurance using distributed algorithms

paper_content:

Many of the nation's airspace users desire more freedom in selecting and modifying their routes. This desire has been expressed in the free flight concept, which has gained increased attention in the last few years. Free flight offers the potential for more efficient routes, decreased fuel costs, and less dependence on air traffic control. The greatest challenge, however, is maintaining the safe separation between aircraft. This problem is often referred to as conflict detection and resolution (CD and R). This paper describes a technique by which aircraft may simultaneously and independently determine collision-free flight operational environment. The technique derived from potential-field has demonstrated tremendous robustness in of scenarios ranging from simple two-aircraft conflicts and contrived geometric formations to complex, randomized multi-aircraft conflicts. Communication failures and restrictive maneuverability constraints have also been considered. The results of this work suggest that potential field algorithms are an extremely robust solution to the problem of CD and R. The results also show that these algorithms can be adapted to a situation requiring distributed computation and resolution. The advantage of a distributed approach is the decreased reliance on a central command authority.
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paper_title: Conflict Resolution Advisory Service in autonomous aircraft operations

paper_content:

Recent advances in air traffic Communication Navigation and Surveillance (CNS) have encouraged investigations into the concept following which Air Traffic Control functions can be delegated to the flight deck, allowing more freedom of movement to airspace users. In late 1995, an initiative, known under the project name FREER, for Free-Route Experimental Encounter Resolution, was introduced at EUROCONTROL to investigate the feasibility of this concept. In this paper, we present the initial results obtained from the Autonomous Aircraft Operations study (FREER-I) that targets full delegation of ATC to aircraft operating in low-density airspace. Specific issues of Autonomous Aircraft Operations (AAO) supporting free-route, free flight and user-preferred routing are discussed. A description of the current prototype illustrating the Airborne Interactive Conflict Resolution Advisory service is included.
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paper_title: Resolution of Conflicts Involving Many Aircraft via Semidefinite Programming

paper_content:

An auto-sequencing associative store provides outputs during a read operation which at least partially forms the search argument for the next store cycle to improve the speed of operation in a data processor.
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Title: A Review of Conflict Detection and Resolution Modeling Methods

Section 1: CONFLICT DETECTION AND RESOLUTION PROCESSES
Description 1: This section defines conflict and describes the core processes involved in conflict detection and resolution (CD&R).

Section 2: CATEGORIZATION OF MODELING APPROACHES
Description 2: This section provides a literature review and categorizes different modeling approaches used in conflict detection and resolution.

Section 3: State Propagation
Description 3: Discusses the methods used for state propagation to predict future aircraft positions and possible conflicts.

Section 4: State Dimensions
Description 4: Describes how models use state information in different dimensions, such as horizontal, vertical or both.

Section 5: Conflict Detection
Description 5: Explains the methods by which models determine the occurrence of conflicts.

Section 6: Conflict Resolution
Description 6: Discusses the various resolution strategies modeled for resolving conflicts, including prescribed, optimized, force field, and manual approaches.

Section 7: Resolution Maneuvers
Description 7: Details the types of maneuvers (turns, vertical maneuvers, speed changes) models predict or advise for conflict resolution.

Section 8: Multiple Conflicts
Description 8: Explains how models handle scenarios involving multiple aircraft conflicts.

Section 9: Other Model Elements
Description 9: Details additional factors such as coordination between aircraft, uncertainty management, and the specific metrics used for CD&R decisions.

Section 10: SYSTEM DESIGN PROCESS ISSUES
Description 10: Discusses the system design processes and methodologies used to develop and tune CD&R systems.

Section 11: IMPLEMENTATION ISSUES
Description 11: Explores operational issues including human performance, integration with existing systems, and computational efficiency.

Section 12: CONCLUDING REMARKS
Description 12: Summarizes the findings and suggests areas for future research and model improvement in conflict detection and resolution.