Method of manufacturing a tail assembly for a rotorcraft; the tail assembly including: - a power transmission shaft covered by at least one non-load bearing fairing; and - a load bearing structure defining, from fore to aft, a tail boom and a tail fin; wherein the load bearing structure has a fore end and a longitudinal median boom portion extending from the fore end towards the tail fin; the power transmission shaft penetrates inside the tail fin by a passing through opening in the load bearing structure; the passing through opening facing forwards longitudinally the fore end; characterized in that the method includes: - a transition stage of providing the load bearing structure of the tail assembly with at least one transition structure that is longitudinally arranged between the longitudinal median boom portion and the tail fin; the non-load bearing fairing being detachably secured to the longitudinal median boom portion for allowing access to the power transmission shaft and being flush with a longitudinal part of the transition structure; at least one transverse section (14, 15) of the transition structure having an upwards dimension that is higher than an elevation junction dimension of the longitudinal median boom portion at a junction between the longitudinal median boom portion and the transition structure; - a cut-out arrangement stage of providing the transition structure with at least one cut-out elevation step, the passing through opening being made in said cut-out elevation step, such that the power transmission shaft extends at least partly externally above the longitudinal median boom portion between the fore end and the cut-out elevation step, the power transmission shaft penetrating in the load bearing structure through the passing through opening; - an upper location stage of determining a longitudinal distance shift at which an upper end of the cut-out elevation step is longitudinally shifted forwards relative to a leading edge of the tail fin; and - a lower offset stage of defining a lower offset at which a lower end of the cut-out elevation step is longitudinally shifted forwards with respect to the upper end of the cut-out elevation step. - a power transmission shaft covered by at least one non-load bearing fairing; and - a load bearing structure defining, from fore to aft, a tail boom and a tail fin; wherein the load bearing structure has a fore end and a longitudinal median boom portion extending from the fore end towards the tail fin; the power transmission shaft penetrates inside the tail fin by a passing through opening in the load bearing structure; the passing through opening facing forwards longitudinally the fore end; - a transition stage of providing the load bearing structure of the tail assembly with at least one transition structure that is longitudinally arranged between the longitudinal median boom portion and the tail fin; the non-load bearing fairing being detachably secured to the longitudinal median boom portion for allowing access to the power transmission shaft and being flush with a longitudinal part of the transition structure; at least one transverse section (14, 15) of the transition structure having an upwards dimension that is higher than an elevation junction dimension of the longitudinal median boom portion at a junction between the longitudinal median boom portion and the transition structure; - a cut-out arrangement stage of providing the transition structure with at least one cut-out elevation step, the passing through opening being made in said cut-out elevation step, such that the power transmission shaft extends at least partly externally above the longitudinal median boom portion between the fore end and the cut-out elevation step, the power transmission shaft penetrating in the load bearing structure through the passing through opening; - an upper location stage of determining a longitudinal distance shift at which an upper end of the cut-out elevation step is longitudinally shifted forwards relative to a leading edge of the tail fin; and - a lower offset stage of defining a lower offset at which a lower end of the cut-out elevation step is longitudinally shifted forwards with respect to the upper end of the cut-out elevation step. - a cut-out arrangement stage of providing the transition structure with at least one cut-out elevation step, the passing through opening being made in said cut-out elevation step, such that the power transmission shaft extends at least partly externally above the longitudinal median boom portion between the fore end and the cut-out elevation step, the power transmission shaft penetrating in the load bearing structure through the passing through opening; - an upper location stage of determining a longitudinal distance shift at which an upper end of the cut-out elevation step is longitudinally shifted forwards relative to a leading edge of the tail fin; and - a lower offset stage of defining a lower offset at which a lower end of the cut-out elevation step is longitudinally shifted forwards with respect to the upper end of the cut-out elevation step.