A mathematical model of the control system of a mobile crane is presented in the paper. The system controls the slewing motion of the chassis as well as it is applied in the model of the emergency subsystem which changes the jib reach. The latter one is initiated at the moment when the threat of loss of stability occurs. Some results of numerical analysis are presented in this paper. The results are related to different strategies of control of the slewing motion as well as to different types of controllers applied in the main loop of control and emergency subsystem. The results of experimental studies are reported as well. The experiments were performed using custom-built testing setup, which represents a kinematic model of a crane.