A Review of Conflict Detection and Resolution Modeling Methods <s> D. Conflict Resolution <s> 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) <s> BIB001 </s> A Review of Conflict Detection and Resolution Modeling Methods <s> D. Conflict Resolution <s> 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. <s> BIB002 </s> A Review of Conflict Detection and Resolution Modeling Methods <s> D. Conflict Resolution <s> 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). <s> BIB003
The Resolution column shows the method by which a solution to a conflict is generated. Five categories are included here: Prescribed (P), Optimized (O), Force field (F), Manual (M), and no resolution (-). Prescribed resolution maneuvers are fixed during system design based on a set of predefined procedures. For example, GPWS issues a standard "Pull Up" warning when a conflict with terrain exists. GPWS does not perform additional computation to determine an optimal escape maneuver. AILS  and Carpenter & Kuchar BIB001 assume that a fixed climbing-turn maneuver is always performed to avoid traffic on a parallel runway approach. Prescribed maneuvers may have the benefit that operators can be trained to perform them reflexively. This may decrease response 13 time when a conflict alert is issued. However, prescribed maneuvers are less effective, in general, than maneuvers that are computed in real time since there is no opportunity to modify the resolution maneuver -the maneuver is performed open-loop to some extent. In many conflicts, it will be necessary to adapt the resolution maneuver to account for unexpected events in the environment, or to reduce the aggressiveness of the maneuver should the conflict be resolved more easily than first predicted. Optimization approaches typically combine a kinematic model with a set of cost metrics. An optimal resolution strategy is then determined by solving for the trajectories with the lowest cost. TCAS, for example, searches through a set of potential climb or descent maneuvers and selects the least-aggressive maneuver that still provides adequate protection  . This requires the definition of appropriate cost functions -typically projected separation, or fuel or time, but costs could also cover workload. Developing costs may be fairly straightforward for economic values but difficult when modeling subjective human utilities. Because current interest in this field is generally centered on strategic resolution of conflicts before immediate tactical evasion is required, economic costs and operator workload will be important to the system design. Some of the models denoted as using Optimized conflict resolution apply techniques such as game theory, genetic algorithms, expert systems, or fuzzy control to the problem. Expert system methods use rule bases to categorize conflicts and decide whether to alert and/or resolve a conflict. These models can be complex and would require a large number of rules to completely cover all possible encounter situations. Additionally, it may be difficult to certify that the system will always operate as intended, and the "experts" used to develop or train the system may in fact not use the best strategy in resolving conflicts. However, a rule base, by design, may be easier for a human to understand or explain than an abstract mathematical algorithm. Force field approaches treat each aircraft as a charged particle and use modified electrostatic equations to generate resolution maneuvers. The repulsive forces between aircraft are used to define the maneuver each performs to avoid a collision. A force field method, while attractive in the 14 sense that a conflict resolution solution is continuously available using relatively simple equations, may have some pathologies that require additional consideration before they can be used in operation. For example, force field methods may assume that aircraft continuously maneuver in response to the changing force field, or that aircraft can vary their speed over a wide range. This requires a high level of guidance on the flight deck and increases complexity beyond issuing simple heading vectors, for example. Additionally, sharp discontinuities in the commanded resolution maneuvers may occur that require additional processing or filtering to arrive at physically feasible solutions. Several human-in-the-loop implementations of the force field method, however, appear to have resolved these problems and have shown that force field resolution can be effective when properly applied BIB002  BIB003 . Some models allow the user to generate potential conflict resolution solutions and obtain feedback as to whether the trial solution is acceptable. These models are denoted as handling a Manual solution in the table. The benefit of a manual solution is that it is generally more flexible in the sense that it is based on human intuition, using information that may not be available to the automation. For example, weather information that is not available to the CD&R system may be important when considering a conflict resolution maneuver. Automated solutions that do not take relevant environmental information into account will likely produce nuisance solutions that the human finds unacceptable. A "-" in the Resolution column indicates that the model does not provide an explicit output of an avoidance action or feedback on a user-defined trial solution. These models perform conflict detection but are not designed to explicitly consider conflict resolution. In some cases, successful conflict resolution is presumed -the focus of the model is only on detecting or counting conflicts.