1Factors Influencing Blind Collision Risk in En Route Sectors Under Free-Flight Conditions

We developed a simulation model of the flight of aircraft through an en route sector. We used the model in two experiments. The first studied the effect of directional clumping on risk. The second was a full factorial design with replication, which simulated a large number of scenarios to assess the impact of key input factors on free flight risk measures. We measured risk for a given flight by the mean distance of closest approach to other aircraft and the mean number of approaches closer than a specified distance. Using analysis of variance and regression analysis, we determined the most important influences on blind collision risk. The most important factors were time of entry into the sector and number of aircraft. Also influential were certain orientations of flight paths and the distribution of airspeeds. The least important factor was altitude. The relationship between number of aircraft and the two risk measures could be quantified in regression relationships. 3Overview The airspace over the US is congested, with a high and growing volume of traffic. In the interests of safety, the congestion is made worse by the constraint that aircraft be routed through a series of pre-established airways where they can be subject to the positive control of air traffi