This research paper presents a toolchain for requirements-based aircraft performance optimisation, applied to a hybrid-electric motor glider. The hybrid powertrain of the airborne platform consists of a battery system and a fuel cell system. During the development of a new aircraft and its propulsion system, certification-relevant requirements must be met. Additionally, the objective is to achieve optimal aircraft performance, such as maximising range. The proposed toolchain enables the optimisation towards specific goals, for instance maximum range, while ensuring compliance with certification requirements. In this study, the degree of hybridisation is treated as a variable to enhance the range of the aircraft while maintaining regulatory compliance. This results in improved performance due to the optimised sizing of the battery and fuel cell system. The final configuration of the aircraft under consideration achieves 1385 km compared to nearly 680 km in the initial configuration.