A mathematical collision risk model is available for evaluating the safety of air route systems. The model requires several parameters associated with navigational accuracies of aircraft. This paper estimates the probability of lateral overlap of pairs of proximate aircraft, which is one of the key parameters of the model, or a given lateral separation minimum. The method of estimation is based on the interpolation of a fitted curve to the empirical distribution of relative lateral distance (=the difference between lateral deviations of a pair of aircrft) obtained by a height finding radar. The curves are determined by using the minimum AIC (Akaike Information Criterion) estimation techniques for several probability density function (pdf) models. The results of analyses show that the pdf of relative lateral distances may be approximated by a family of the double-double exponential (DDE) distribution. The estimated probability of lateral overlap for the same assigned route, Py(0), is 3.00×10^<-2> under observational conditions.
