A model is described of directional coupled two-phase composite growth in three dimensions using a combined cellular automaton finite difference (CAFD) approach. The modelling strategy and some preliminary results are presented here for the first time. The model incorporates solute diffusion and a simple cellular automaton growth rule containing a pseudo-curvature algorithm. Despite its limitations, the model is able to simulate some of the structural effects that take place during coupled growth. As a demonstration application the model is applied to eutectic growth in the Pb-Sn system and compared to experimental measurements. The scale of predicted microstructures in the model is close to that measured after directional freezing of Pb-Sn eutectic.