It's Time for Sustainable Aviation: Discrete-Event Life Cycle Assessment of Emerging Aircraft Technologies

Kurzfassung

Global air traffic is growing rapidly and is projected to expand over the next decades. This growth is in direct tension with international climate targets. Aviation is a significant contributor to global emissions, and emerging aircraft technologies, such as hydrogenpowered and hybrid-electric concepts, offer potential for emission reductions. Yet, their environmental performance remains difficult to assess. Life cycle assessment is an established method for evaluating a wide range of environmental impact indicators throughout the life cycle of an aircraft. Conventional life cycle assessment approaches rely on static, averaged assumptions of aircraft operation and often neglect the dynamic interplay of flight events, maintenance constraints, and component replacement cycles. This dissertation comprises five interconnected studies that develop a discrete-event life cycle assessment framework and apply it to both conventional and novel aircraft concepts. The framework models the entire aircraft lifetime as time-explicit events, with particular emphasis on maintenance activities and flight operations, thereby capturing the dynamic nature of the aircraft life cycle. Maintenance activities remain vastly underrepresented and are often dismissed as environmentally negligible despite being a mandatory precondition for safe and continued flight operations. To address this, a top-down analysis of maintenance checks is combined with a bottom-up assessment of individual tasks derived from the aircraft manufacturer's maintenance planning document. The results show that the environmental impacts are not evenly distributed throughout the life of the aircraft. Especially heavy maintenance checks, engine shop visits, and certain component replacements lead to substantially higher impacts while associated aircraft downtimes directly reduce transport capacity. Maintenance-related impacts are further shown to be highly sensitive to factors such as the flight schedule or maintenance management practices. Flight operations present an equally fundamental challenge. Around one third of aviation's climate impact stems from carbon dioxide (CO2) emissions, while the remaining share arises from non-CO2 effects, such as contrail formation, water vapour, or nitrogen oxides (NOX). These are highly dependent on flight altitude, routing, and atmospheric conditions and cannot be adequately captured by conventional life cycle assessment approaches. Coupling the discrete-event life cycle assessment with an atmospheric climate response model enables the assessment of aircraft across different operational conditions. This is demonstrated through a comparative analysis of a turbofan and a turboprop aircraft with different flight schedules and fuel types. The results highlight that integrating non-CO2 effects into life cycle assessment substantially improves the representativeness of environmental assessments in aviation. These methodological foundations are subsequently applied to two emerging aircraft concepts with distinct technological characteristics. The first is a hydrogen-powered aircraft with cryogenic liquid hydrogen tanks, an integrated fuel cell system, and an advanced hydrogen propulsion and distribution system. Existing life cycle assessment studies of hydrogen-powered aircraft rarely account for the operational implications of novel maintenance requirements and largely overlook uncertainties arising from the limited data availability of prospective technologies. To address these gaps, the discrete-event life cycle assessment is combined with probabilistic uncertainty characterisation. While hydrogen technologies can substantially reduce overall environmental impacts relative to conventional aircraft, these benefits come with important trade-offs: production and maintenance of additional components generate higher on-ground impacts, and new safety requirements introduce longer and more frequent maintenance downtimes that reduce operational capacity. The hydrogen tank emerges as a particularly critical component, given its uncertain in-service lifetime and material-intensive replacement. The second concept is a hybrid-electric aircraft, with batteries being a key determinant of its environmental impact. A semi-empirical battery degradation model is integrated into the discrete-event life cycle assessment framework to represent charging strategies, battery ageing, and replacement cycles. The results reveal a trade-off between operational efficiency and environmental performance. Longer turnaround times enable slower charging, which is less damaging to the battery and reduces the number of replacements over the aircraft lifetime, while lowering both life cycle CO2 emissions and material demand. This benefit, however, comes at the cost of lower aircraft utilisation. Across all studies, the findings confirm that the operational phase remains the dominant contributor to aviation's environmental impact. At the same time, ground-based life cycle phases reveal burden-shifting effects that static assessment approaches systematically overlook. The developed discrete-event life cycle assessment framework therefore advances dynamic assessment methodology for aviation and provides a more realistic basis for evaluating emerging aircraft technologies.