This paper presents preliminary results of the application of the Parameter Space Investigation method for the design of the ℒ 1 flight control system implemented on the two turbine-powered dynamically-scaled GTM AirSTAR aircraft. In particular, the study addresses the construction of the feasible solution set and the improvement of a nominal prototype design, obtained using the systematic design procedures of the ℒ 1 adaptive control theory. On the one hand, the results in the paper demonstrate the benefits of ℒ 1 adaptive control as a verifiable robust adaptive control architecture by validating the theoretical claims in terms of robustness and performance, as well as illustrating its systematic design procedures. On the other hand, the paper confirms the suitability of the Parameter Space Investigation method for the multicriteria design optimization of a flight control system subject to desired control specifications. Also, in order to facilitate the multicriteria analysis process, this study takes advantage of the Multicriteria Optimization and Vector Identification software package, which was designed to apply the Parameter Space Investigation method to engineering problems. The results and conclusions of this paper have contributed to the improvement of the (predicted) flying qualities and the robustness margins of the all-adaptive ℒ 1-augmented GTM AirSTAR aircraft.