Computer Simulation of Near Midair Collisions in the Terminal Environment

Abstract

A computer simulation of near midair collisions in a terminal environment is developed and its capability demonstrated in a simplified case. The motion of several aircraft is described with certain constraints imposed on the speed, flight path, and other parameters to restrict the aircraft movement to lie within actual operating limitations. The main purpose of this study is to test the feasibility of the approach as far as general complexity, computer execution time, and accuracy. The results indicate good agreement with applicable theoretical arguments as well as additional information relating frequency and severity of near midair collisions to miss distance and aircraft density .Also, the advantage of the computer simulation technique is discussed. MATHEMATICAL modeling of flight operations in the terminal environment for the purpose of studying air-toair conflicts has only lately been developed. Recent work has contributed a which estimates the frequency of near midair collisions (NMACs) in a terminal area.1 Its purpose was to determine the computational workload of an automated collision avoidance system. In performing this task, turning rate, aircraft speed, rate of climb, warning time, type of flight (IFR or VFR),t and various other parameters were utilized. Another study has examined the number of aircraft operations and the number of reported NMACs for CY-1968 in each of the twenty-one large air transportation hubs.2 The results of this particular study was a terminal air traffic which showed a high correlation for a quadratic relationship between aircraft population or density and the number of reported NMACs. This fact reinforces the hypothesis that a model is applicable. Alexander3 and Graham-Orr,4 using this approach have indicated that a square law exists between NMACs and aircraft density. However, a gas has obvious limitations. Namely, aircraft do not possess a velocity spectrum comparable to gas molecules and, in general, lack the randomness to be treated in the macroscopic sense. In fact, the gas approach is becoming a poorer approximation even for an upper bound since increased radar control of aircraft, including VFR aircraft, in terminal areas eliminates the randomness required for analytic solutions. Also implicit in some (not all) NMACs is the human element of surprise. One pilot may be startled by a close approach of another aircraft, while the other pilot would simply consider the approaching aircraft as routine traffic. Thus, obviously not all close approaches are reported as near midair collisions.