## 5 Outlook and Conclusions  
This study describes the potential of different operational changes to reduce the climate impact of aviation and presents a method to compare individual measures. The proposed method scales the mitigation potentials of the individual measures to one common reference considering differences in traffic sample size as well as different CO\({}_{2}\) and non-CO\({}_{2}\) climate effects, thus enabling a comparison of the climate impact of the considered operational measures. As a result, we identify significant climate mitigation potentials both in-flight and on-ground. Higher absolute potentials can be achieved with in-flight measures compared to on-ground ones considering both CO\({}_{2}\) and non-CO\({}_{2}\) emissions. However, in-flight mitigation measures are generally associated with lower maturity levels and a more negative impact on the involved stakeholders of the air transport system. For example, shifting trajectories to less climate-sensitive regions can potentially reduce airspace capacity, increase workload, particularly for pilots and air traffic controllers, and raise direct costs for aircraft operators. Other measures have a lower mitigation potential but can be considered 'low-hanging fruits' as the enabling technology is mature, the operational concept is clear, and their impact on performance, human workload and operation safety is relatively small. This is, for example, the case for the electrification of the ground support equipment and operations, and the upgrade of the airport infrastructure according to energy-efficiency criteria. In future work, this study could be expanded to further operational improvements as well as by assessing the effects of implementation enablers on the KPI changes caused by individual measures. Moreover, results need extension to a broader scope, e.g., also including regional operations or worldwide flights, to increase significance. A direct quantitative comparison of measures of different types requires higher consistency regarding reference case definition and modeling assumptions. A more detailed investigation of the stakeholder effects, in addition to investments and cost changes, is of further interest, for instance by assessing increases in airspace complexity due to the implementation of trajectory changes or changes in on-ground processes due to the implementation of airport-related improvements. Moreover, a combination of several methods as well as including technological improvements such as new aircraft concepts or sustainable fuels could enrich the achieved results. Conceptualization, Z.L.Z., S.D.G. and F.L. ; methodology, Z.L.Z., F.L., M.C. and S.D.G. ; software, Z.L.Z., S.D.G., M.C., B.B., M.N., P.R., E.B., M.G. and C.A. ; validation, Z.L.Z. and M.C. ; data curation, Z.L.Z., S.D.G., B.B., P.P., M.N., P.R., E.B., M.G. and C.A. ; writing--original draft preparation, Z.L.Z., S.D.G. and C.A. ; writing--review and editing, M.C., F.L., V.G., B., P.P., S.M., M.N., P.R. and A.T.; visualization, Z.L.Z. and S.D.G. ; supervision, F.L., V.G. and S.M. ; project administration, S.D.G., F.L., I.O. and A.T.; funding acquisition, F.L., I.O. and A.T. All authors have read and agreed to the published version of the manuscript. **Funding:** This research is part of the project ClimOP, which is funded by the European Union's Horizon 2020 Research and Innovation Programme under Grant Agreement number 875503. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The data presented in this study are available on request from the corresponding author as long as they do not underlie any additional license conditions. Restrictions apply to Sabre Market Intelligence data and BADA4 aircraft performance data. **Acknowledgments:** The author would like to thank the full ClimOP consortium as well as the members of the project's advisory board for their support in preparing the achieved results and the fruitful discussions.