A variety of assessment methods are used in assessing performance in complex domains. These vary from paper-and-pencil tests to advanced simulation. The conventional approach to assessment of airline pilots' performance has focused on technical skills, such as flying an aircraft and related aeronautical knowledge including aerodynamics, aircraft systems, navigation, rules and regulations. While technical skills are important, over recent decades another set of pilot skills has been implicated in a majority of airline accidents. These skills, termed non-technical skills, include decision making, communication and teamwork. Although critical to airline safety, these non-technical skills are only now beginning to be transparently assessed. This paper presents empirical research that investigated current practice in how experienced senior pilots assess pilot performance. The research has led to a model for assessing pilots? performance (MAPP). Whilst this model has been developed for use in aviation, the paper discusses how the MAPP may have relevance to other professions and vocations for assisting in complex performance-based assessment.