In view of the constant trend toward reducing the mass of aircraft engine components, gears dynamics has assumed an increasingly important role in the development of new products. The reduction in component mass entails a decrease in their dimensions as well as an increase of their flexibility, making some phenomena associated with high rotational speeds no longer negligible. In this context, the present thesis, carried out in collaboration with GE Avio Aero, represents a preliminary study for the multibody analysis of complex transmission systems by means of the MSC.Adams software. After an initial phase devoted to the modelling of rotors with multiple degrees of freedom, a model of a compound gearbox was developed to analyze the effects that micro-geometry modifications, combined with the non-negligible deformations of the components, exert on the system dynamics.