A method for assembling a gas turbine engine assembly includes coupling a fan assembly to a core gas turbine engine such that the fan assembly is upstream from the core gas turbine engine, coupling a low-pressure turbine downstream from the core gas turbine engine such, wherein the low-pressure turbine includes a disk and a plurality of splines formed in the disk, providing a shaft that includes a first end and a second end that includes a plurality of splines, coupling the shaft first end to the fan assembly, and coupling the shaft second end to the low-pressure turbine such that the shaft splines mesh with the disk splines such that torque is transmitted from the low-pressure turbine to the fan assembly via the shaft during engine operation.