Terminal air traffic flow and collision exposure

The actual incidence of midair collisions and near midair collisions in terminal areas between controlled and uncontrolled traffic can be expected to depend on the number of aircraft operations, the relative location and utilization of airports and runways in each terminal, the restrictions on the use of the terminal airspace imposed by topographical features and arrival/departure routes, the incidence of marginal visibility, and the effectiveness of traffic advisories warning of potentially conflicting traffic. This paper shows that the relative incidence of collision exposure in the various terminals, as measured by the number of hazardous near midair collisions reported in these terminals during the 1968 FAA Near Midair Collision Study, is accounted for to a remarkable extent by the relative number of operations and the relative degree to which controlled and uncontrolled aircraft share the same airports. Only a very few specific terminals, where the unequal influence of the other factors cited is believed to be significant, depart somewhat from this finding.