## 2 Materials and Methods
### Aviation Fuels and Previous Sustainability Studies
[36] provided comprehensive overviews of this field. Accordingly, drop-in SAFs based on biomass, also referred to as biokerosene, receive particular attention in the current literature (e.g., [19; 20; 24; 37; 38; 39; 40]). In the aforementioned studies, the general impact of biokerosene instead of kerosene and its production based on different feedstocks are analyzed. The existing studies show that lignocellulosic biomass (e.g., miscanthus), starch and sugar, as well as vegetable oils and fats are potential feedstocks [19]. They can be further processed using various production routes (e.g., FTS, HEEA, HTL, Atl, or DSHC) [19; 20]. Using these BtL pathways, reductions in GHG emissions of 63-89% in a well-to-wake perspective are achievable compared with fossil kerosene [20; 37]. These reductions depend highly on the underlying electricity mix in the production. If the biokerosene is produced based on the current electricity mix, the GHG emissions are approximately 2.4 times higher than for fossil kerosene along the life cycle. Therefore, the use of electricity based on RE is an important lever to reduce climate-damaging GHG emissions [41]. In addition to GHG emissions, scientific discourse explores land use for cultivating first- and second-generation feedstocks. In this context, it has become clear that feedstocks of the second generation especially are considered promising due to low competition for the cultivation of food crops. However, the focus should be on feedstocks of the third generation in the long term [39; 40]. Studies with an economic focus mainly evaluate the competitiveness of biokerosene compared to fossil kerosene, and its market penetration potential is analyzed. The analyses indicate that biokerosene has significantly higher production costs, mainly due to the higher energy demand and the resulting higher energy costs. Further improvements in the production processes are required to reduce energy consumption and improve production efficiency [24; 38]. Aside from biokerosene, synthetic kerosene based on the PtL pathway is seen as a potential solution to reduce the environmental impact and for transitioning the aviation sector from fossil to renewable fuel, thereby leveraging existing aircraft systems and  
Figure 1: Classification and production pathways of aviation fuels (adapted from [32]). airport infrastructure. Synthetic kerosene based on PtL pathways produces less GHG emissions along the life cycle than fossil kerosene and consumes less land and water during production than biokerosene. However, its production is still problematic, as it is very energy-intensive. A high share of RE in the electricity mix is again required to decrease its environmental impacts. Analogous to biokerosene, the high energy demand results in higher production costs [19]. In addition to drop-in fuels, several studies exist on the sustainability aspects of non-drop-in fuels (e.g., [41; 42; 43; 44]). Liquid hydrogen especially is of particular interest due to its advantages in terms of GHG emissions, acidification, summer smog, and eutrophication compared with fossil kerosene. However, these advantages can only be exploited if the electricity for hydrogen production comes from renewable sources, resulting again in high production costs. Since hydrogen is a non-drop-in fuel, it requires structural changes and extensive modifications of the aircraft powertrain. The previous studies in the scientific literature mainly focus on the analysis of environmental aspects associated with the production and use of biokerosene. These are compared with fossil kerosene to analyze their potentials. However, economic aspects are only considered to a limited extent. Furthermore, there are only a few studies on synthetic kerosene, and a comprehensive comparative analysis of fossil kerosene, biokerosene, and synthetic kerosene in the well-to-wake perspective is missing in the scientific literature so far.