This paper reviews two major programmes for support of pilot decision making in a fighter aircraft: the US Pilot's Associate and the French Copilote Electronique. In addressing the problem of decision support in a highly complex and time-pressurised environment, both programmes migrated from a traditional expert systems approach to one based on cognitive modelling. This, however, is where most commonality ends. The paper shows how the differences between the programmes can be explained in terms of their assumptions of what constitutes pilot expertise. These views explain the method for analysis of pilot activities, the model of the pilot, what phase of the pilot's problem solving the programmes attempt to support, and the support philosophy. The paper concludes with a discussion on computer-based decision support in complex, dynamic domains, and how cognitive modelling may contribute.