Aviation companies show great interest in Structural Health Monitoring (SHM) systems. Although noticeable effort has been put into this research field, so far no system is ready for industrial use. One of the major issues is the processing of complex signals caused by complex aerospace structures. Numerical simulations can help to comprehend these signals, but are often unable to cope with the model detail required. A ray tracing algorithm to approximate Lamb wave propagation is proposed, which enables a huge model reduction. The resulting minimal model mainly consists of the border lines of areas with different geometrical or material properties. Finite element simulations are used to determine the interaction behavior of these transition zones. A two stage concept is used to find paths from an actuator to a sensor and calculate time signals.