To participate in the transition towards a sustainable use of energy, the aircraft sector needs to be transformed with respect to the energy carrier and propulsion methods. For smaller aircraft, a battery-electric approach is promising. While this will require extensive research and design together with the application of advanced components which are partly not available to this date, general design rules and key parameters and critical components can already be deduced. This publication presents the example design of the full propulsion system for a small commuter aircraft. This serves as a case study to highlight the influence of components and parameters on the overall efficiency and weight of the system. By that, future research can be directed towards the areas of high impact on the realization of all-electric aircraft. A optimization of several motor variants, inverter topologies and power supply grid parameters is performed. The weight of the fully electric propulsion system is dominated by the battery. Therefore, all subsequent components need to be designed towards a high efficiency in opposition to high power density.