The DLR Institute of Air Transport is researching ways to enable climate-compatible aviation and is investigating, among other things, how optimised flight trajectories can reduce both fuel consumption and CO2 emissions, as well as non-CO2 effects such as the formation of contrails.
A key objective of the institute’s work is to reduce the overall climate impact of air transport through the development and application of trajectory optimisation methods. This involves analysing technical, operational, and policy measures in terms of their feasibility, cost, and societal relevance.
What Are Flight Trajectories?
A flight trajectory describes the exact path of an aircraft from take-off to landing, defined by its lateral flight route and vertical flight profile, including flight times, speeds, and other technical parameters. It serves, among other things, as the planning basis for reducing non-CO2 effects. Through targeted adjustments to a trajectory, fuel consumption can be lowered, areas of high climate sensitivity can be avoided, or the total emissions of a flight can be minimised.
Why Research into Climate-Optimised Flight Trajectories Matters
Aviation contributes to global warming not only through CO2 emissions but also via non-CO2 effects such as contrails and ozone formation resulting from nitrogen oxide emissions. Targeted trajectory planning can mitigate these effects but often requires detours or alternative cruising altitudes and is highly dependent on current weather conditions. These deviations from fuel-optimised operations generally result in higher operational costs. A key research challenge, therefore, is to identify ways to make climate-optimised flying effective as well as economically and regulatorily viable.
Climate-Sensitive Regions Around 10,000 m Above Sea Level
Climate-sensitive regions with potential for the formation of persistent contrails.
Climate-optimised flight trajectories have the potential to significantly reduce aviation’s climate impact and thus contribute to achieving the goals of the Paris Agreement. By mitigating non-CO2 effects, this concept can help limit the environmental impact of growing air traffic. Building on this, the development and implementation of regulatory measures aim to enable systematic recording and reporting of climate-relevant effects and to promote targeted mitigation procedures.
Research Focus
One of our main research areas in climate-compatible aviation is the development and testing of operational procedures to reduce the climate impact of air transport. Climate-optimised trajectories represent one of several possible procedural approaches. At the Institute of Air Transport, we also explore technological solutions, such as propulsion technologies and alternative fuels, which we model and assess within the operational context.
Technical Measures (Selection)
Targeted use of sustainable fuels such as SAF (Sustainable Aviation Fuels)
New aircraft and propulsion concepts (hybrid, hydrogen-based, battery-electric)
Operational Measures (Selection)
Avoidance of climate-sensitive regions through climate-optimised trajectories
Multi-step flight operations
Targeted adjustment of altitude and speed
Formation flying
Regulatory Measures (Selection)
Scientific support for the introduction of regulations addressing non-CO₂ effects
Integration into emissions trading schemes
Climate-sensitive restricted areas or toll systems
Measures to Reduce the Climate Impact of Air Transport
The implementation of climate-optimised flight trajectories raises a number of scientific questions. Uncertainties in weather forecasting and in the modelling of non-CO2 effects complicate reliable estimates of the expected climate impact, which are necessary for sound flight planning. Although these uncertainties can be reduced, they cannot be completely eliminated in the medium term. They must therefore be taken into account in trajectory planning and optimisation to minimise the risk of misguided adjustments. In addition, operational implementation requires efficient coordination among all stakeholders.
At the same time, it is essential to maintain a balance between ecological effectiveness and economic feasibility to ensure that measures are both practical and sustainable. This balance forms a central area of tension that guides both our research and regulatory decision-making processes.
Networks and Cooperation
The DLR Institute of Air Transport collaborates closely on these topics with partners within DLR—such as the Institute of Atmospheric Physics—as well as with external stakeholders including Airbus, Deutsche Lufthansa AG, TUIfly GmbH, European Air Transport Leipzig GmbH, Deutsche Flugsicherung GmbH, the European Commission (DG CLIMA), the German Meteorological Service (DWD), and the German Environment Agency (UBA). The institute also participates in national and international committees.
Current Research Projects
Our research on climate-optimised flight trajectories is conducted within specific projects. For instance, our institute advises the EU on the introduction of an MRV (Monitoring, Reporting and Verification) system for non-CO2 effects. In the LuFo (German Aviation Research Programme) demonstrator project D-KULT, real flights are planned and conducted as part of the so-called “100 Flights Trial”. Using available climate impact models and weather data, we test climate-optimised trajectories, thereby practically demonstrating the feasibility of eco-efficient flight routes under real conditions.
