A 10%-scale high-lift version of the Common Research Model (CRM-HL) was tested in the NASA Langley Research Center’s 14 by 22 ft subsonic tunnel. The focus of the wind-tunnel tests was to investigate the vortices generated at the nacelle/pylon region and their effect on the aerodynamic performance. The wind-tunnel measurements included the acquisition of force and moment data, steady pressure data, as well as surface flow visualization using minitufts. For some select cases, numerical simulations were performed to aid in understanding the wind-tunnel data. Wind-tunnel tests, with and without the nacelle/pylon, indicated a lift degradation of the conventional CRM-HL at high angles of attack. The surface flow visualization with fluorescent minitufts revealed that the lift degradation is due to flow separation caused by the nacelle/pylon vortex system on the inboard wing. The consequent flow separation was successfully mitigated using a nacelle chine installed on the inboard side of the engine nacelle.