Air traffic contributes to anthropogenic global warming by about 5% due to CO₂ emissions and non-CO₂ effects, which are primarily caused by the emission of NO_x and water vapor as well as the formation of contrails. Since-in the long term-the aviation industry is expected to maintain its trend to grow, mitigation measures are required to counteract its negative effects upon the environment. One of the promising operational mitigation measures that has been a subject of the EU project ATM4E is climate-optimized flight planning by considering algorithmic climate change functions that allow for the quantification of aviation-induced climate impact based on the emission’s location and time. Here, we describe the methodology developed for the use of algorithmic climate change functions in trajectory optimization and present the results of its application to the planning of about 13,000 intra-European flights on one specific day with strong contrail formation over Europe. The optimization problem is formulated as bi-objective continuous optimal control problem with climate impact and fuel burn being the two objectives. Results on an individual flight basis indicate that there are three major classes of different routes that are characterized by different shapes of the corresponding Pareto fronts representing the relationship between climate impact reduction and fuel burn increase. On average, for the investigated weather situation and traffic scenario, a climate impact reduction in the order of 50% can be achieved by accepting 0.75% of additional fuel burn. Higher mitigation gains would only be available at much higher fuel penalties, e.g., a climate impact reduction of 76% associated with a fuel penalty of 12.8%. However, these solutions represent much less efficient climate impact mitigation options.

Aviation can reduce its climate impact by controlling its CO₂-emission and non-CO₂ effects, e.g., aviation-induced contrail-cirrus and ozone caused by nitrogen oxide emissions. One option is the implementation of operational measures that aim to avoid those atmospheric regions that are in particular sensitive to non-CO₂ aviation effects, e.g., where persistent contrails form. The quantitative estimates of mitigation potentials of such climate-optimized aircraft trajectories are required, when working towards sustainable aviation. The results are presented from a comprehensive modelling approach when aiming to identify such climate-optimized aircraft trajectories. The overall concept relies on a multi-dimensional environmental change function concept, which is capable of providing climate impact information to air traffic management (ATM). Estimates on overall climate impact reduction from a one-day case study are presented that rely on the best estimate for climate impact information. Specific weather situation that day, containing regions with high contrail impact, results in a potential reduction of total climate impact, by more than 40%, when considering CO₂ and non-CO₂ effects, associated with an increase of fuel by about 0.5%. The climate impact reduction per individual alternative trajectory shows a strong variation and, hence, also the mitigation potential for an analyzed city pair, depending on atmospheric characteristics along the flight corridor as well as flight altitude. The robustness of proposed climate-optimized trajectories is assessed by using a range of different climate metrics. A more sustainable ATM needs to integrate comprehensive environmental impacts and associated forecast uncertainties into route optimization in order to identify robust eco-efficient trajectories.

Air traffic management as currently under development by the Single European Sky ATM Research program SESAR has an important role to play in reducing environmental impact of aviation by means of green trajectories, in addition to the improvements to be derived from new aircraft and engine technologies. A comprehensive modelling approach is presented which allows identifying aircraft trajectories having a lower environmental impact compared to the fuel optimal solution. Algorithmic environmental change functions are introduced which allow determining impact of aircraft emission at a given position and time from standard meteorological forecast parameters. A case study for three city-pairs is presented using reanalysis meteorological data. Mitigation potential of environmentally optimized trajectory options is analyzed, using a set of different climate impact metrics identifying robust routing options. This study presents results for a multi-criteria environmental assessment of aircraft trajectories relying on an advanced MET service as developed within the Exploratory Research Project ATM4E (SESAR2020). This framework allows studying and characterizing changes in traffic flows due to environmental optimization, as well as studying trade-offs between distinct strategic measures.

Impacts of commercial aircraft operation upon the environment, which are caused primarily from emissions of CO2, NOx and the formation of contrails, are matter of growing concern, as aviation is one of the fastest developing industrial sectors worldwide and the awareness of its effects is expanding. Recent research has focused on the cost-benefit potential of different mitigation strategies, which optimize flight trajectories with respect to climate and economy, but most of these mitigation strategies cannot be implemented in the near future due to technical challenges.The objective of this paper is to present an interim mitigation strategy, which bridges this time period. In analogy to military exclusion zones, climate restricted airspaces (CRA) are defined based on 3-D climate change functions, characterizing the environmental impact caused by an aircraft emission at a certain location. Regions with climate costs greater than a threshold value are closed in the corresponding month; others are cleared for air traffic. To estimate the cost-benefit potential of this strategy, a preliminary analysis is conducted on the route from Helsinki (EFHK) to Miami (KMIA). Affected flight trajectories are re-routed optimally around resulting CRA with regard to monetary costs for varying threshold values. Therefore, flight simulation algorithms are developed, which solve a non-linear optimal control problem. For each optimized flight trajectory corresponding average temperature response (ATR) and cash operating costs (COC) are expressed relative to a reference great circle trajectory with constant Mach number and compared with the climate mitigation potential of climate optimized trajectories.

Climate optimized flight trajectories are considered to be a promising measure to mitigate non-CO₂ emissions’ environmental impact, which is highly sensitive to locus and time of emission. Within this study, optimal control techniques are applied in order to determine 2D (lateral) and 3D (lateral and vertical) cost-optimized flight trajectories while mitigating their climate impact by minimizing emissions and flight time in highly climate sensitive regions. Therefore, monetary and 4D-climate cost functions, describing the climate sensitivity in dependency of the emission location, altitude, time and weather situation, are integrated into the optimization algorithm. For both, 2D- and 3D-optimization, the cost-benefit potential (climate impact mitigation vs. rise in operating costs) is investigated for nine fictitious North Atlantic routes for eastbound and westbound directions in the presence of winds. The conducted study shows large potential for both measures as the reduction of climate sensitivities along the trajectory often predominates the additional emissions caused by headwinds, additional climb-and descent phases, additional flight distance, and off-design altitudes. Flight trajectories optimized within the horizontal plane can reduce the average temperature response (ATR) by approximately 15 % for a two percent increase in cash operating costs (COC). This mitigation potential is significantly improved by superposition of lateral and vertical optimization. 3D-optimized trajectories which are comparable in cost increase achieve a 20-35 % higher ATR reduction than their 2D-optimized counterparts. Further, they reduce global warming more efficiently (higher ATR reduction per unit cost increment) and to a higher extent. However, achieving maximum climate impact mitigation is linked with an disproportional rise of cash operating costs in both cases. Therefore, a careful consideration of the required climate impact savings as well as the accepted surcharges is necessary.