Active magnetic bearings(AMBs) present a technology which has many advantages compared to traditional bearing concepts. However, they require backup bearings in order to prevent damages in the event of a system failure. In this study, the dynamics of an AMB supported rotor during impact on backup bearings is studied employing a detailed simulation model. The backup bearings are modeled using an accurate ball bearing model, and the model for a flexible rotor system is described using the finite element approach with the component mode synthesis. Not only the influence of the support stiffness, clearance and friction coefficient on the rotor orbit, but also bearing load are compared for various rotor system parameters. Comparing these results it is shown that the optimum backup bearing system can be applicable for a specific rotor system.