A rotary propulsion system for a tiltrotor aircraft operable to transition between rotary and non rotary flight modes. The rotary propulsion system includes an engine that is coupled to a freewheeling unit. A gear system has a torque path coupling assembly between a first gear assembly that is coupled to the freewheeling unit and a second gear assembly that is coupled to a proprotor assembly. The torque path coupling assembly has an engaged position wherein the output of the first gear assembly is coupled to the input of the second gear assembly thereby providing a torque path between the engine and the proprotor assembly. The torque path coupling assembly also has a disengaged position wherein the output of the first gear assembly is independent of the input of the second gear assembly thereby interrupting the torque path between the engine and the proprotor assembly.