A turboshaft engine, which is typically used as a rotorcraft engine, offers a high-speed output, whereas the rotor of a rotorcraft features a low rotational speed; therefore, considerable speed reduction is required to transmit power from the engine to the rotor. The gears of the first reduction stage for high-speed input are typically mounted either on a turboshaft engine or on a main gearbox that is separate from the engine. Similar to most rotorcraft components, these gears require weight minimization. The specifications of a helical gear set for the first reduction stage are determined while accounting for weight minimization. The specifications for the gear are calculated using an optimization method involving NSGA-III. The gear helix angle is a key determinant of the support bearings to be used. Hence, the gear specifications are calculated for a case with an unfixed helix angle and for four cases with fixed helix angles. The gear train of each case, which contains gears, shafts, and bearings, is modeled using SMT MASTA (a gearbox design software). The weight change of the gear train with respect to the helix angle is investigated.