Research in the field of human-computer interaction (HCI) has shown that early usability evaluation of human interfaces can reduce operator errors by optimizing functions for a specific population. HCI research has produced many methods for evaluating usability, which have proven effective in developing highly complex computer systems. Given the importance of the human in the loop in aviation systems, it is possible that advanced commercial cockpit and air traffic control systems may benefit from systematic application of usability research. This article identifies the special requirements of the aviation domain that will affect a usability evaluation and the characteristics of evaluation methods that may make them effective in this context. Recommendations are made of usability evaluation techniques, or combinations of techniques, most appropriate for evaluating complex systems in aviation technology.