In this paper flight instrument panels, main user-interfaces of multi-purpose civil helicopters are studied. Current arrangement approaches for instrument panels are studied and analyzed and a new user-centered design method is developed for civil rotary-wing aircraft that can be described as an interface optimization based on user opinions and preferences. An interview was conducted among 15 helicopter pilots constituted the first step of the research. In the second phase of the research, a paper prototyping method has been applied on helicopter pilots. The proposal of an optimization method of instrument panel arrangement based on user opinions is the primary output of the study. The optimum instrument panel design is, constructed depending on an approach, in which locating displays on the instrument panel using their average locational values and then making revisions over the first design, using interview findings and pilots' opinions and preferences. As the result of both interview and experimental studies; it has been observed that the principle of functional grouping of displays is the primary consideration of users. Additionally, two new concepts, "inseparability relation" and "locational value" has been proposed by the researcher.