D-KULT: data and tools for routine eco-efficient flight operations

The climate effect of aviation is significant and expected to increase. Reducing the sector's environmental footprint to contribute to global temperature targets will require not only investments in airframe and engine technologies but also operational strategies such as eco-efficient flight routing. The D-KULT project (Demonstrator Climate and Environmentally Friendly Air Transport), funded under the German Federal Aviation Research Programme (LuFo) demonstrated the operational feasibility of integrating climate-response estimates of non-CO ₂ effects into flight trajectory optimisation in practice. The project addressed a multi-objective optimisation problem. Flight trajectories were optimised to minimise climate effects based on climate response estimates from numerical models while maintaining operational and economic efficiency. Operational constraints such as meteorological hazards, regulatory requirements, airspace and airport capacity were incorporated to ensure real-world applicability. D-KULT developed an end-to-end information chain integrating aviation weather forecasting, flight planning, air traffic control, and climate benefit assessment to enable eco-efficient flight routing for testing purposes. Achieving this complex operational and environmental objective required close collaboration across multiple disciplines and substantial upgrades to the majority of participating components. Advanced aviation weather products were generated that estimate the climate response to emissions under prevailing meteorological conditions. Flight planning tools have been extended to incorporate this information in addition to the standard data used in the flight planning optimization algorithms. In this way, flight planning tools can calculate emissions and corresponding climate effects along flights, both as part of pre-tactical and tactical (pre-take-off and in-flight) eco-efficient flight optimisation. Developments within D-KULT were tested through a large-scale national contrail avoidance flight trial campaign (TF-100 with 108 flights), including enhanced satellite-based contrail detection methods and assessment of estimates of climate benefits. Further evaluation focused on operational integration, examining air traffic control procedures, and workflow implications in a high-fidelity simulator environment. This manuscript provides a comprehensive overview of the project, describes new developments and major challenges on implementation pathways, summarizes key findings and gives recommendations derived from practical implementation. Issues that still need to be solved are: Aviation weather forecast should be based on improved cloud microphysics representing ice supersaturation correctly, humidity measurements at cruise altitudes are required for data assimilation, the geographical and temporal scope of implemented response tools needs to be extended. Since different meteorological input data and different response tools lead to differing assessments of climate benefits and damages, such sensitivities need to be considered in accordance with a thorough uncertainty analysis. For future implementation practical obstacles are the automation of procedures, the increase of workload for controllers if climate sensitive sectors need to be kept clear of aircraft, and the subject of standardization.