Hazard avoidance alerting with Markov decision processes

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004.Includes bibliographical references (p. 123-125).(cont.) (incident rate and unnecessary alert rate), the MDP-based logic can meet or exceed that of alternate logics.This thesis describes an approach to designing hazard avoidance alerting systems based on a Markov decision process (MDP) model of the alerting process, and shows its benefits over standard design methods. One benefit of the MDP method is that it accounts for future decision opportunities when choosing whether or not to alert, or in determining resolution guidance. Another benefit is that it provides a means of modeling uncertain state information, such as unmeasurable mode variables, so that decisions are more informed. A mode variable is an index for distinct types of behavior that a system exhibits at different times. For example, in many situations normal system behavior tends to be safe, but rare deviations from the normal increase the likelihood of a harmful incident. Accurate modeling of mode information is needed to minimize alerting system errors such as unnecessary or late alerts. The benefits of the method are illustrated with two alerting scenarios where a pair of aircraft must avoid collisions when passing one another. The first scenario has a fully observable state and the second includes an uncertain mode describing whether an intruder aircraft levels off safely above the evader or is in a hazardous blunder mode. In MDP theory, outcome preferences are described in terms of utilities of different state trajectories. In keeping with this, alerting system requirements are stated in the form of a reward function. This is then used with probabilistic dynamic and sensor models to compute an alerting logic (policy) that maximizes expected utility. Performance comparisons are made between the MDP-based logics and alternate logics generated with current methods. It is found that in terms of traditional performance measuresby Lee F. Winder.Ph.D

Performance evaluation of evasion maneuvers for parallel approach collision avoidance

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, February 1999.Includes bibliographical references (leaves 55-56).Current plans for independent instrument approaches to closely spaced parallel runways call for an automated pilot alerting system to ensure separation of aircraft in the case of a "blunder," or unexpected deviation from the normal approach path. Resolution advisories by this system would require the pilot of an endangered aircraft to perform a trained evasion maneuver. The potential performance of two evasion maneuvers, referred to as the "tum-climb" and "climb-only," was estimated using an experimental NASA alerting logic (AILS) and a computer simulation of relative trajectory scenarios between two aircraft. One aircraft was equipped with the NASA alerting system, and maneuvered accordingly. Observation of the rates of different types of alerting failure allowed judgement of evasion maneuver performance. System Operating Characteristic (SOC) curves were used to assess the benefit of alerting with each maneuver. This analysis shows the climb-only maneuver to be a poor substitute for the turn­climb. For a 2500 ft runway spacing and an expected 2 sec pilot reaction time, and with the nominal alerting threshold settings chosen by NASA for the tum-climb, false alarms during blunders are approximately 40 times as likely to induce collisions when using the climb­only as when using the tum-climb, and 40 times as many collisions occur during blunders with the climb-only overall. SOC analysis shows that the safety possible with the climb­only is difficult to distinguish from having no alerting system at all. With the tum-climb there is a clear safety benefit. Alerting performance with the tum-climb is also more resistant to errors in trajectory prediction and evasion maneuver execution.by Lee F. Winder.S.M