In the highly uncertain environment of conceptual aircraft design and technology assessment and selection, making good decisions is of utmost importance. Aiming to contribute to improving decision quality, the problem was researched from both a technical as well as a socio-psychological perspective. In the technical perspective, the uncertainty associated to three two-dimensional aerodynamic solvers -- following from physical flow model assumptions or numerical solution method differences -- was quantified and propagated. It was found that the influence of flow model clearly outweighs the impact of solution method. Although the aircraft synthesis program used for uncertainty propagation showed very little sensitivity to the effects of the assumptions investigated, these results raise critical questions about the currently observed push for higher-fidelity analysis methods in aircraft conceptual design. In the socio-psychological perspective, document review, interviews and observations were used to define what socio-psychological factors negatively impact group decision making in an international public-private research consortium aiming to contribute to aircraft fuel burn reduction through R&D concept development. Based on vigilant interaction theory and (the conceptual foundations of) effective intercultural workgroup communication theory, a theoretical framework was used to develop the TARE-model, which helps groups balance task (TA) and relationship (RE) outcomes in an uncertain environment. Using a thought experiment, the inherent integration and inseparability of the two perspectives was found. Uncertainty was put forward as the primary variable impacting the interwovenness of the two perspectives. Applying this conclusion to the results from the technical and socio-psychological domains, the question is raised whether increased computational power and additional models are the most effective way to substantially improve the quality of decisions in conceptual design and technology assessment and selection projects.