An eye movement study has been conducted to investigate if and how visual groupings are formed for an aircraft conflict detection task (ACDT) with multiple moving targets. We define visual grouping (VG) as a group of two or more targets in which a participant's eye movements have shown a greater number of transitions between or among the targets. In order to identify and compare the VGs, a short algorithm is proposed and evaluated. The experiment results reveal that VGs can be captured and clustered. Also, the clustered VGs are identical to the uncertain pair(s) of aircraft that may have loss of separation (LOS) under co-altitude. This study is one necessary step in performing further eye movement studies to better understand cognitive processes for a dynamic task, especially an ACDT.