A new steady approach has been developed to predict the transonic buffet onset of a high speed aircraft. In this paper, the flow is assumed to be steady for the buffet onset. The present study involves the analysis of a distinct change in the variation of various static aerodynamic parameters. These distinct changes indicates the onset of transonic buffet. Among the various aerodynamic parameters considered in this study, the variation in the center of pressure has shown to provide a clearest indicator of transonic buffet onset. This new steady approach can be applied to predict the transonic buffet onset for airfoils with shock induced separation bubble and for large swept wings with small aspect ratios. Good agreements have been obtained compared with unsteady wind tunnel buffet test data. Based on the results obtained the new steady approach, it can be newly suggested that the distinct slope changes of the center of pressure curve can be used as an indicator of buffet onset for the steady experimental method on a full aircraft configuration.