Sonic boom attenuation is a considerable design challenge to enable civilian aircraft to operate at supersonic ight conditions. One technology proposed by Gulfstream Aerospace Corporation for the production of low-noise supersonic aircraft is the high-fl ow nacelle bypass concept in which an outer nacelle surface is used to encircle the asymmetric external engine protuberances of a traditional turbine engine. Although this bypass flow may reduce the overall sonic boom signature of the vehicle, the engine gearbox and protuberances create a highly complex 3-D flow in the annular bypass region. To better understand the 3-D flow features, an approximately 1/6th engine model was tested in a newly constructed 11.1 inch diameter axisymmetric test section of a subsonic wind tunnel at the University of Illinois at Urbana Champaign. By rotating the test section, pressure measurements were obtained over a range of circumferential angles and radial positions. The pressure measurements were used to create planar maps of nondimensionalized total and dynamic pressure upstream and downstream of the bypass model. Wind tunnel testing was performed on the empty axisymmetric wind tunnel followed by model configurations of increasing complexity until a full test configuration of the engine model with the gearbox fairing and crane beam mounts was achieved. Results show significant pressure loss behind the gearbox fairing further characterized using surface flow visualization. Due to the blockage created by the gearbox fairing mounted at the underside of the model, results also show increased fl ow velocity in the upper section of the bypass duct.