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Reducing Emissions from Aviation by Changing Trajectories for the Benefit of Climate

State of the Art - Background

Despite the significant progress that has been made in reducing the specific emissions of aircraft, in particular CO2, the absolute emissions have been increasing rapidly during the recent decades and are projected to continue to grow. Furthermore, aviation substantially impacts upon the climate through non-CO2 effects such as ozone formation and methane destruction from aviation's NOx emissions, the formation of contrails and contrail cirrus, the emission of H2O at high altitudes, emission of aerosols (e.g. soot) and aerosol precursors (e.g. SOx), which are directly radiatively active and which modify cloudiness and cloud micro-physical and radiative properties.

Current flight planning is performed with the objectives of achieving maximum punctuality or minimizing the operational costs, whereas the target of minimal fuel consumption, minimal CO2 emissions or minimal climate impact has a lower priority.

Impact of aircraft non-CO2 emissions on the atmospheric composition and on the climate depends on the altitude and location of the emissions. Therefore climate impact via NOx, contrails and contrails cirrus can be reduced, for example, by flying lower and avoiding contrail regions. On the other hand this results in a higher fuel burn and hence in higher CO2 emissions.

The project REACT4C will perform an optimisation approach for alternative or environmental flight planning in order to assess the potential for reducing fuel consumption, CO2 emissions and climate impact from aviation.


In order to reduce aviation's emissions and improve its environmental compatibility, the project REACT4C will address those inefficiencies which exist in the aviation system with respect to fuel consumption and emissions by investigating the potential of alternative flight routing for lessening the atmospheric impact of aviation.

Hence, the main objectives of REACT4C are:

- to explore the feasibility of adopting flight altitudes and flight routes that lead to reduced fuel consumption and emissions, and lessen the environmental impact, and

- to estimate the overall global effect of such ATM measures in terms of climate change.

The objective of REACT4C is to demonstrate that environmentally-friendly flight routing is feasible, but does not address the operational implementation of such advanced Air Traffic Management (ATM) procedures. The latter would require much more time than is available during the present project. However, REACT4C will deliver substantial scientific foundation and operational specification for novel ATM procedures, which might be explored in a later phase of the SESAR JU. Analogously, REACT4C will deliver fundamental concepts of aircraft that are better suited for environmental flight routing, which will have the potential to enter the Clean Sky JTI in a later phase.

Description of Work

We plan to achieve the objectives of REACT4C mainly by a numerical approach, which combines atmospheric models of different complexity, ATM tools of planning flight trajectories, including models to calculate aircraft emissions, and tools for aircraft pre-design.

The work plan of REACT4C is structured into nine Work Packages (WPs) such that each individual work package is as compact as possible and that interfaces among different work packages can be kept as simple and efficient as possible (see also figure).

We begin with the selection of weather situations (WP1). Climate cost functions are determined for these weather situations (WP2) and then fed into a flight planning tool to calculate environmentally-friendly flight trajectories and emissions and climate impact along these trajectories (WP3). Finally, the results are evaluated and uncertainties are estimated (WP4).

The potential for mitigating the atmospheric effect of aviation are further explored (WP5) and how aircraft design can be optimized with respect to environmentally friendly flight routing is studied (WP6).

The findings of the project will be aggregated to recommendations for future ATM, aircraft design and research (WP7). Specific WPs on coordination and exploitation (WP8) and management of the project (WP9) complement the above structure.

Expected Results

The expected results are:

- An initial scoping study of expanding an operational flight planning tool by optimisation against criteria of fuel consumption and emissions will be performed; the inclusion of climate cost functions will enable environmentally friendly flight planning with respect to climate impact;

- The project will, for the first time, quantify the potential for improvements of inefficiencies in the air transport system with respect to fuel consumption, emissions and climate impact due to non-conventional flight trajectories under realistic atmospheric conditions on a regional and global scale.

- For the first time, 4D climate cost functions (as functions of latitude, longitude, altitude and time) will be calculated for realistic weather situations. These cost functions will rely on different emission metrics of climate change, targets being time integrated marginal Radiative Forcing RF (in analogy to the Kyoto metric Global Warming Potential) and temperature change after a given time horizon (the Global Temperature Potential);

- The project will allow the formulation of specific recommendations for stakeholders on flight planning, aircraft and engine design for future green aircraft;

- Cooperation will be instigated between complementary experts required for environmental flight planning, which has the potential to initiate follow-up joint work in Clean Sky JTI and SESAR JU.

Graphical presentation of project structure,showing work packages and interaction
Graphical presentation of project structure, showing work packages and interaction.