The Concurrent Subspace Design (CSD) framework has been used to conduct a preliminary design optimization of an aircraft landing gear subsystem. The application required the implementation of the MDO framework with existing industrial analysis software. The CSD framework employs artificial neural networks to provide approximations to the design space, which are the means of coordinating design decisions in the individual disciplines. This approach was applied to the design of an aircraft brake actuation system which contains continuous and discrete design variables. The results demonstrate that the mixed CSD framework was able to efficiently identify improved designs. This study also demonstrated that the CSD framework can be exploited using existing engineering analysis methods.