Separation of air traffic by visual means: An estimate of the effectiveness of the see-and-avoid doctrine

Using the 1968 FAA near midair collision data and Howell´s flight test data on visual detection of aircraft from other aircraft, an estimate is made of the effectiveness of the see-and-avoid doctrine as a function of closing speed in today´s air traffic environment. It is estimated that at present about 95 percent of potential collisions are avoided at low closing speeds; this effectiveness of see and avoid falls to about 50 percent above 400 knot closing speed. Midair collisions are found to be primarily attributable to the failure by pilots to see the other aircraft in time to maneuver, and an estimate is given of the potential reduction in anticipated collision rates achievable with the use of pilot warning indicator systems of various degrees of effectiveness. The probability that a pilot reports an NMAC is found to increase as the closing speed of the encounter increases, but it also appears that pilots tend to underestimate the miss distance at the high closing speeds. The estimates made of the probability of successful maneuvers are in good agreement with the independent results of simulation experiments. The expected number of midair collisions in the various closing speed ranges, as predicted from the NMAC and Howell data, are in reasonable agreement with experience.