HIGHLIGHT: REACT4C - An Approach for a weather-dependent climate-optimized Fight Planning to mitigate Aviation Climate Impact

Mitigation of aviation climate impact is one strategic goal spelled out for a durable development of air traffic. One option to mitigate aviation climate impact are operational measures for route optimisation by air traffic management (ATM). We present a comprehensive approach developed within the collaborative project REACT4C (Reducing Emissions from Aviation by Changing Trajectories for the benefit of Climate) funded under the European FP7 programme in order to establish a decision support tool to identify such environmental or climate-optimized trajectories. Objective of this collaborative research project coordinated by the author of this study is to explore feasibility of adopting flight altitudes and flight routes that lessen the environmental and climate impact. Second objective is to estimate the overall global effect of such ATM measures in terms of climate change.

Total climate impact of aviation is caused by CO2 and non-CO2 aviation emissions, which both need to be addressed when aiming to minimize climate impact as they are in the same order to magnitude. Climate impact of non-CO2 emissions depends on time and position of aircraft, as atmospheric processes leading to climate change vary with background conditions and transport pathways within the atmosphere. Hence, by considering this spatial dependence of climate impact a mitigation potential for minimizing overall climate impact exists and can be accessed by an integrated approach of flight planning. However, such information is in general not available during flight optimisation. Here, REACT4C has expanded a flight planning tool in order to be able to identify climate-optimized flight trajectories.

We present the overall modelling chain set-up for climate-optimized flight planning, stretching from aviation meteorology over climate impact and leading to climate-optimized flight trajectories. First step is characterisation of meteorological situations for daily weather conditions with respect to spatial and temporal dependence of atmospheric response and climate impact of aviation emissions. This information needs to be made available for flight trajectory optimisation. Interface between climate impact and flight planning is established via climate cost functions, which quantify atmospheric climate response (sensitivity) to aviation emissions depending on latitude and time. A conventional flight planning tool is expanded with these 4-d functions in order to perform optimisation with regards to total aviation climate impact. Climate cost 4-d functions are calculated with a Lagrangian approach in a comprehensive atmospheric climate-chemistry model which allows to study the fate of aviation emissions in the atmosphere and related climate impact. The expanded flight planning tool then calculates trajectories under specific optimisation criteria, i.e. minimal costs and minimal climate impact.

In order to evaluate overall mitigation potential of such alternative flight planning, a classification of typical weather situations was performed and detailed flight optimisation is performed for each archetypical pattern identified. Based on these detailed flight planning an estimate of the mitigation potential on an annual basis can be provided. The development of this modelling chain is complemented by scientific studies which explore the uncertainty of our procedure and related atmospheric processes. Among aviation climate impact we consider in detail CO2, NOx (via formation ozone and influence on methane), soot, contrail and contrail-cirrus.

Scientific expertise within the interdisciplinary consortium allows to jointly set up such a modelling chain which brings together meteorology, chemical and climate impacts of aviation emissions, with operational aspects of flight planning. The objectives of REACT4C are mainly achieved by a numerical approach, which combines atmospheric models of different complexity, air traffic management (ATM) tools for planning flight trajectories and models to calculate aircraft emissions with tools for aircraft pre-design. University of Reading (UK) in collaboration with UK Met Office identifies typical weather situations (classification) and characterises them, including their statistical probability. DLR Institute of Atmospheric Physics (Germany) jointly with CICERO (Norway) calculates for each selected weather situation, radiative forcings and 4d climate cost functions for unit emissions at predefined mission location. Eurocontrol Experimental Centre (France) calculates conventional and climate optimized flight trajectories. Simultaneously, the related incremental reduction in emissions and climate change is estimated. In a joint effort the potential total (global and annual) mitigation gain from environmental flight planning is computed, and the uncertainties in the mitigation gain from environmental flight planning are estimated. Atmospheric scientists from Manchester Metropolitan University (UK), DLR Institute of Atmospheric Physics (Germany), CICERO (Norway), University of Aquila (Italy) prepare a multi-model climate impact assessment, and derive uncertainties of related atmospheric processes. Aircraft pre-design concepts are explored by Airbus (France) in collaboration with DLR for climate-optimized trajectories. Recommendations for later implementation of proposed climate optimized flight planning as practical rules with a focus on meteorological information are deduced.

Objective is to identify alternative flight altitudes and flight trajectories that lead to reduced overall climate impact, and to estimate potential benefit of such operational measures. A way forward how to implement such climate-optimized flight planning will be suggested.