## 5 Conclusions and Outlook  
This study scrutinized the potential of substituting fossil kerosene with different types of SAFs on medium-haul flights. By doing so, the environmental and economic impacts related to the use of the SAFs compared with fossil kerosene were analyzed by conducting an environmental and economic assessment, and the advantages as well as disadvantages were identified. The study focused on the fuel supply chain and flight operation in the use stage. The results of the study reveal that SAFs can be partially advantageous in environmental aspects. However, at the current state of development and considering the prevailing production conditions of the fuels, fossil kerosene is to be preferred. Concerning the economic impacts, SAFs are not yet competitive, and political measures must promote their use (e.g., substitutions, subsidies, or tax measures). The drivers of the negative environmental and economic impacts are mostly the high energy demand in fuel production as well as the current composition of the electricity mix based on fossil sources. However, it can be assumed that this composition will shift toward a higher share of RE in the long term. Subsequent scenario analyses showed that using an electricity mix of 100% based on RE could further reduce the environmental impacts in six of the seven impact categories investigated. It is particularly noticeable that the SAFs, which are energy-intensive to produce, thus became competitive with fossil kerosene from an environmental point of view. Only the impact category MRD deteriorated due to the RE plants to be built. Therefore, SAFs produced by RE can be a solution for reducing the environmental impacts of the aviation sector and contribute to the achievement of the Flightpath 2050 goals. This study can be a starting point for future research. The results give an overview of the environmental and economic impacts of different types of aviation fuels and thus enable a detailed comparison. In future research, further fuels need to be added, such as third-generation biokerosene or SAFs produced by HEFA, HTL, AtJ, DSHC, or StL. In this context, different synthesis processes have to be considered, and alternative process routes for production of the fuels or required feedstocks (e.g., hydrogen) can be integrated. In this way, the most promising SAFs can be identified at an early stage and become a focus of further research. In addition, spatial differentiation must be examined, especially in the fuel supply chain. On the one hand, countries with a higher share of RE in the electricity mix can be advantageous for the production of SAFs (and vice versa). At the same time, countries with low energy costs exist, which can offer economic advantages. If these aspects are taken into account through more advanced spatial differentiation in the fuel supply chain, supply chain configurations associated with less environmental and economic impacts can be designed. However, critical working conditions prevail in less developed countries, and a conflict of objectives of the three pillars of sustainability may occur. Therefore, a social analysis should be integrated. While SAFs can contribute to a sustainable aviation sector in the short term, novel propulsion technologies for aircraft have to be integrated in the long term, as proposed by [PERSON] et al. [15,78]. These include non-drop-in fuels (e.g., liquid hydrogen) that require modification of the powertrain as well as the use of novel propulsion technologies (e.g.,battery-based or fuel cell-based concepts). Both approaches will be necessary to achieve the long-term emission reduction goals of the aviation sector. Considering different market entry times will allow the development of transition pathways to a sustainable aviation sector, considering short-term and long-term sustainability objectives. Overall, this article expands the scientific literature by creating novel LCI datasets for a well-to-wake analysis of fossil kerosene and four types of SAFs.