Most of the industrial software codes used for the prediction of the radar cross-sections (RCS) of aircraft are based on ray tracing. While ray based methods give useful scattered fields from the skin of the aircraft illuminated by an incident plane wave, they largely fail to predict the returns from onboard cavities, such as the jet engines. As a possible enhancement to these ray-tracing programs, an auxiliary program based on the modal method was developed to predict the scattering of electrically large and complex jet inlets and engines. Monostatic RCS measurements of a 0.706 m diameter test cylinder containing 30 skewed blades mounted on a center shaft with a conical hub have been performed at X-band. The dimensions of the structure and the number and orientation of the blades are consistent with existing jet engines. Good agreement between predictions and measurements verify the developed software and analytical method used.