In the United States alone, there has been an average of 12.4 mid-air collisions of General Aviation (GA) aircraft resulting in an average of 19.1 fatalities per year between 1991 and 2008.  In order to determine where the risk of a mid-air collision is highest, the narratives of NTSB mid-air collision accident reports from January 2000 until June 2010 were analyzed (total of 112). All accidents were separated into three categories based on their proximity to the airport. 

The geometry for each collision was analyzed. Then, the geometry of all mid-air cillisions was visualized using one half of a compass rose (see Figure 1).

To gain a better understanding of each of the environments identified in the first step, the geometries were also visualized for all three of them (Figure 2-4).

In summary, a mid-air collision is most likely to occur between two aircraft going in the same direction. The location with the most reported mid-air collisions is the airport pattern (59%) with most of them occuring on final or short final.

The attached document gives a broader summary as well as evaluates the implications of these findings.