Abstract: In a gas turbine bypass engine having an inlet for gas flow to a core duct and an outer duct for bypassing a portion of the inlet air flow around such core duct, an improvement is provided in which a plurality of pivotal outlet guide vanes mounted on the rear frame member, aft of the low-pressure turbine, the vanes being hollow and upstanding edgewise in the path of the core gas with each vane mounted to pivot on an axis extending through the length thereof, with means to pivot the vanes on their axes so as to correct the swirl of turbine discharge gases toward axial flow through the nozzle of such engine, during high bypass ratio and low bypass ratio operation.