The applications of sandwich structures in industry are numerous. The optimizations of such structures with high strength and light weight have been the topic of interest for many researchers. This paper presents the coupled structural-acoustic simulation of sandwich structures for global transport aircraft applications.These studies employ a flexible uniform thin cylindrical shell as the model of the sandwich structure for global transport aircraft. The Galerkin and the Rayleigh-Ritz methods are used to obtain the coupled modal equations for the system which are solved using a state space formulation. Numerical simulation results are presented which show the mode shapes of the coupled system, it would provide the reference to the coupled structural-acoustic systems optimization.