Uncertainty is present throughout the aircraft design process and is of key importance during the preliminary design stage. At the same time there is often insufficient understanding of the governing process to warrant a detailed description of an uncertainty model, which often leads to neglecting the issue altogether. In this paper we present the foundation of a framework for propagating uncertainty through black-box computer models organically integrated into highly flexible parametric geometry models. We form this foundation by focusing on the interval as a building block of uncertain numbers. We compare the reliability and efficiency of the uncertainty representation provided by various interval propagation methods by applying them to an early-stage geometric model of an electric motor mount.