Successful performance in complex operating environments requires that operators function with a level of proficiency in cognitive skills such as situation awareness, planning, problem-solving, and decision-making. However, assessing the application of these skills within the operational environment has been difficult, to the extent that their application is often simply inferred on the basis of a set of behavioural responses. The broad aim of the present study is to develop a tool to identify the application of cognitive skills within the applied environment. Twenty-one experienced airline pilots participated in a series of cognitive interviews in which they were asked to describe the tasks that they engage during a flight. Preliminary analyses suggest that different phases of flight are associated with different levels of cognitive complexity and can be used as a basis to test the validity of a cognitive assessment tool.