## 2 Materials and Methods
### Assessment Method  
Various methods for sustainability assessment were developed to assess the environmental, economic, and social impacts associated with products, processes, and supply chains. Common methods for quantification of the environmental impacts related to an object of investigation include life cycle assessment (LCA), carbon footprinting, cumulative energy demand, material flow analysis, and environmental impact assessment [45; 46]. Next to the environmental assessment methods, several economic assessment methods, such as life cycle costing (LCC), techno-economic assessment, or the net present value method, are available [46; 47]. Recently, the assessment of social impacts has also become increasingly important. In this context, methods such as social life cycle assessment, social sustainability evaluation, or human development analysis are used to quantify the social impacts of an object of investigation [18; 46; 48]. In addition to this wide range of methods for assessing specific sustainability dimensions, some approaches enable a holistic sustainability assessment of environmental, economic, and social impacts. A widely established quantitative assessment method is the life cycle sustainability assessment approach. It scrutinizes the three pillars of sustainability by merging the environmentally-oriented LCA with the economically-oriented LCC and the socially-oriented social life cycle assessment [45; 49; 50; 51; 52]. This study focuses on analyzing the environmental and economic impacts of fossil kerosene and four SAFs in the well-to-wake perspective. Social analysis is omitted due to the focus on a European supply chain configuration, in which the typically considered social risks in global supply chains, such as child labor, forced labor, or corruption, are negligible, and a meaningful analysis would not be possible. LCA and LCC are commonly used in science and industry for the quantitative sustainability assessment of products and processes. Therefore, they are also applied for the assessment within this article. The basic procedure of the LCA and LCC is derived from the ISO 14040/14044 standards and is divided into four phases: (1) goal and scope definition, (2) inventory analysis, (3) impact assessment, and (4) interpretation [53; 54; 51]. The schematic procedure is presented in Figure 2.  
Typical LCA and LCC start with the definition of the study's goal and the scope, including the definition of the subject of study within the system boundaries. In addition, the functional unit is defined, establishing the reference to which all energy and resource flows are normalized. Next, inventory data describing the exchanges between the unit processes within the system under study and the external environment are collected along the life cycle. The inventory data are assigned to impact categories in the subsequent impact assessment, and the so-called impact scores are calculated. Finally, an interpretation of the assessment results is conducted, taking into account the decision makers' preferences and enabling support for decision making. This step also accompanies the other steps and may be carried out in an iterative procedure, as new insights, data limitations, or stakeholder views can lead to a redefinition of the study's focus, goal, and methods [51, 53, 54, 55]. LCA addresses the environmental impacts of the system under study. The environmental interventions of all processes within the systems' life cycle, such as extraction of natural resources, the release of emissions, or land use, are compiled in the inventory analysis phase. In the subsequent impact assessment, the results of the inventory analysis are linked to different areas of protection (human health, ecosystems, and resources). These so-called endpoint indicators are determined based on midpoint indicators, such as climate change, mineral resource depletion, or photochemical oxidant formation. The midpoint indicators are calculated via characterization factors used to quantify the impact of the environmental interventions [56, 57].