Many attempts have been made to reduce aviation’s environmental impact, as aviation traffic has grown exponentially in recent decades. While some approaches focus on technology and fuel alternatives, others strive to develop improved operational measures within air traffic management as a short-term action to mitigate aviation-induced climate change, as well as air pollution. In this work, different flight procedures are analyzed in terms of emissions and noise impact to define optimal trade-offs. The investigation is based on flight data recorders, emissions, and noise prediction models. An aircraft trajectory simulation code with flight procedure optimization is also implemented to define an environmentally optimal trajectory. The results show that while noise and the emissions proportional to the burned fuel may be reduced for some trajectories, other non-${\mathrm{CO}}_2$ emissions could drastically increase if too low idle-thrust levels are reached. Therefore, a minimum threshold for idle thrust is suggested as a key factor to define a truly optimal trajectory in terms of ${\mathrm{CO}}_2$ emissions, non-${\mathrm{CO}}_2$ emissions, and noise. Full article

Ambient weather conditions strongly impact contrail formation and persistence. The implementation of contrail avoidance and mitigation strategies, therefore, requires regional and altitude-dependent information on the frequency of contrail occurrence. To this end, we have developed a method to quantify the potential contrail cover based on 10 years of high-resolution reanalysis of climatology and weather data from the European Center for Medium-Range Weather Forecast (ECMWF). We use the Schmidt–Appleman threshold temperature for contrail formation and additionally select thresholds for the relative humidity to evaluate the occurrence of persistent contrails and assess their regional and seasonal variation. We find a potential contrail cirrus cover of 10% to 20% above Europe at higher altitudes of 200 and 250 hPa in the 10-year climatology and a weak seasonal variation. At lower altitudes, near 300 hPa, a steep onset and a high potential contrail cirrus cover of 20% is found in late fall and in winter, decreasing to 2% potential contrail cirrus cover in summer. In comparison to ECMWF data, evaluations using data from the National Centers for Environmental Prediction (NCEP) show a significantly lower potential contrail cirrus cover. Our results help to investigate the seasonal and altitude dependence of contrail mitigation strategies, in particular for warming nighttime contrails that contribute strongly to the total climate impact from aviation. Full article

This work presents a transpacific airliner designed for minimal climate impact, incorporating several novel design features. These include open rotor engines, sustainable aviation fuels, natural laminar flow airfoils, and riblets. The design’s configuration and mission have been optimised simultaneously using a combination of standard preliminary techniques, experimental data, a multi-point mission analysis, and a model of average temperature response. It is demonstrated that, on an 8000 km mission, the design offers an 89.8% reduction in average temperature response relative to an Airbus A330-200, at the expense of a 7.3% increase in direct operating cost. The sensitivity of these results is investigated by comparing the performance over a range of operating conditions. In addition, several alternative designs incorporating only some of the above-mentioned features are analysed, allowing for an assessment of their individual contribution. Finally, a life-cycle average temperature response analysis is presented to place the climate impact of operation, manufacturing and end-of-life procedures in context. Full article

The aviation industry has committed to decarbonize its CO₂ emissions. However, there has been much less industry focus on its non-CO₂ emissions, despite recent studies showing that these account for up to two-thirds of aviation’s climate impact. Parts of the industry have begun to explore the feasibility of potential non-CO₂ mitigation options, building on the scientific research undertaken in recent years, by establishing demonstrations and operational trials to test parameters of interest. This paper sets out the design principles for a large trial in the North Atlantic. Considerations include the type of stakeholders, location, when to intervene, what flights to target, validation, and other challenges. Four options for safely facilitating a trial are outlined based on existing air-traffic-management processes, with three of these readily deployable. Several issues remain to be refined and resolved as part of any future trial, including those regarding meteorological and contrail forecasting, the decision-making process for stakeholders, and safely integrating these flights into conventional airspace. While this paper is not a formal concept of operations, it provides a stepping stone for policymakers, industry leaders, and other stakeholders with an interest in reducing aviation’s total climate impact, to understand how a large-scale warming-contrail-minimizing trial could work. Full article

One possibility to reduce the climate impact of aviation is the avoidance of climate-sensitive regions, which is synonymous with climate-optimised flight planning. Those regions can be identified by algorithmic Climate Change Functions (aCCFs) for nitrogen oxides (NO${}_x$), water vapour (H${}_2$O) as well as contrail cirrus, which provide a measure of climate effects associated with corresponding emissions. In this study, we evaluate the effectiveness of reducing the aviation-induced climate impact via ozone (O${}_3$) formation (resulting from NO${}_x$ emissions), when solely using O${}_3$ aCCFs for the aircraft trajectory optimisation strategy. The effectiveness of such a strategy and the associated potential mitigation of climate effects is explored by using the chemistry–climate model EMAC (ECHAM5/MESSy) with various submodels. A summer and winter day, characterised by a large spatial variability of the O${}_3$ aCCFs, are selected. A one-day air traffic simulation is performed in the European airspace on those selected days to obtain both cost-optimised and climate-optimised aircraft trajectories, which more specifically minimised a NO${}_x$-induced climate effect of O${}_3$ (O${}_3$ aCCFs). The air traffic is laterally and vertically re-routed separately to enable an evaluation of the influences of the horizontal and vertical pattern of O${}_3$ aCCFs. The resulting aviation NO${}_x$ emissions are then released in an atmospheric chemistry–climate simulation to simulate the contribution of these NO${}_x$ emissions to atmospheric O${}_3$ and the resulting O${}_3$ change. Within this study, we use O${}_3$-RF as a proxy for climate impact. The results confirm that the climate-optimised flights lead to lower O${}_3$-RF compared to the cost-optimised flights, although the aCCFs cannot reproduce all aspects of the significant impact of the synoptic situation on the transport of emitted NO${}_x$. Overall, the climate impact is higher for the selected summer day than for the selected winter day. Lateral re-routing shows a greater potential to reduce climate impact compared to vertical re-routing for the chosen flight altitude. We find that while applying the O${}_3$ aCCFs in trajectory optimisation can reduce the climate impact, there are certain discrepancies in the prediction of O${}_3$ impact from aviation NO${}_x$ emissions, as seen for the summer day. Although the O${}_3$ aCCFs concept is a rough simplification in estimating the climate impact of a local NO${}_x$ emission, it enables a reasonable first estimate. Further research is required to better describe the O${}_3$ aCCFs allowing an improved estimate in the Average Temperature Response (ATR) of O${}_3$ from aviation NO${}_x$ emissions. A general improvement in the scientific understanding of non-CO${}_2$ aviation effects could make climate-optimised flight planning practically feasible. Full article

Aircraft emissions represent a relevant amount of human induced CO₂. Globally, up to 2.5 per cent of such emissions stem from the aviation industry. In order to investigate the effects within the atmosphere, realistic flight profiles are necessary to provide quantitatively tangible values of emissions. The flight profiles and the according fuel consumption can be calculated by using waypoints from flight plans and Base of Aircraft Data (BADA). This paper presents an approach to refine the fuel consumption by integrating the passenger load into the calculation. Since effects of emissions have to be assessed on a greater scale, such as on the European air traffic network, the presented approach provides cost functions for CO₂ emissions for different aircraft types and load factors. The cost functions were derived by means of regression analyses of BADA based calculated flight profiles with a step size of one second. The calculations are based on real historic traffic scenarios over several days. The derived aircraft specific fuel burn coefficients enable a simple and efficient integration of CO₂ estimations depending on the flight distance, load factor and aircraft type. This can be applied to large traffic scenarios to also study different set-ups such as travel restrictions, other disruptions or an alteration in the traffic system as a whole. In order to enable the assessment of further aspects of such changes to the European air traffic system at large and to foster reproducibility and comparability of related studies, we provide further general-purpose cost estimation functions for several important key characteristics. Besides fuel consumption, we develop cost estimations for air navigation fees and maintenance for conventional aircraft. Those functions are also provided for the design concept of a short-range all-electric aircraft. This propeller aircraft features game-changing technologies such as active laminar flow control, active load alleviation and advanced materials and structure concepts. The approaches discussed in this paper will focus on the generic aspects of aircraft related costs, which can be derived from general available data. For the sake of reproducibility, the results will be made publicly available. Full article

Persistent contrails and contrail cirrus are estimated to have a larger impact on climate than all CO${}_2$ emissions from global aviation since the introduction of jet engines. However, the measure for this impact, the effective radiative forcing (ERF) or radiative forcing (RF), suffers from uncertainties that are much larger than those for CO${}_2$. Despite ongoing research, the so called level of scientific understanding has not improved since the 1999 IPCC Special Report on Aviation and the Global Atmosphere. In this paper, the role of weather variability as a major component of the uncertainty range of contrail cirrus RF is examined. Using 10 years of MOZAIC flights and ERA-5 reanalysis data, we show that natural weather variability causes large variations in the instantaneous radiative forcing (iRF) of persistent contrails, which is a major source for uncertainty. Most contrails (about 80%) have a small positive iRF of up to 20 W m${}^{-2}$. IRF exceeds 20 W m${}^{-2}$ in about 10% of all cases but these have a disproportionally large climate impact, the remaining 10% have a negative iRF. The distribution of iRF values is heavily skewed towards large positive values that show an exponential decay. Monte Carlo experiments reveal the difficulty of determining a precise long-term mean from measurement or campaign data alone. Depending on the chosen sample size, calculated means scatter considerably, which is caused exclusively by weather variability. Considering that many additional natural sources of variation have been deliberately neglected in the present examination, the results suggest that there is a fundamental limit to the precision with which the RF and ERF of contrail cirrus can be determined. In our opinion, this does not imply a low level of scientific understanding; rather the scientific understanding of contrails and contrail cirrus has grown considerably over recent decades. Only the determination of global and annual mean RF and ERF values is still difficult and will probably be so for the coming decades, if not forever. The little precise knowledge of the RF and ERF values is, therefore, no argument to postpone actions to mitigate contrail’s warming impact. Full article

This paper discloses a new algorithm, called sustainable supersonic fuel flow method, to complement the conceptual design of future supersonic aircraft with pollutant and greenhouse gases emissions estimation. Starting from already existing algorithms currently used to assess the environmental impact of already developed and operating aircraft, the authors suggest revisions to improve the formulations, thus extending their application. Specifically, this paper has two objectives: to support the design of future supersonic aircraft and to evaluate the impact of the exploitation of more sustainable aviation fuels, with special focus on biofuels and biofuel blends, since the conceptual design stage. The core of the algorithm developed to predict in-flight emissions of a supersonic aircraft has been validated with public data of Concorde flight experiments. In addition, corrective factors accounting for the most recently developed and certified biofuels have been included in the formulation. Full article

The theory of contrail formation for fuel cells is derived. It is a variant of the well-known Schmidt-Appleman theory. The contrail factor or G-factor for fuel cells is much larger than for jet engines, such that condensation of the exhaust water vapour can happen even at the Earth’s surface in sufficiently cold (a few degrees above zero) weather. Contrail formation from fuel cells will occur frequently in the lower troposphere and is unavoidable below moderate temperature limits, in the upper troposphere and in the stratosphere. Despite the high frequency of contrail formation from fuel cells, their climate impact is lower than that of contrails from jet engines. Most fuel cell contrails will be short and those persistent ones will be optically thinner and have on average a shorter lifetime than traditional persistent contrails. From a climate point of view, the introduction of fuel cells into aviation can be recommended. Full article

The rapid growth of global aviation operations has made its negative environmental impact an international concern. Accurate modeling of aircraft fuel burn, emissions, and noise is the prerequisite for informing new operational procedures, technologies, and policies towards a more sustainable future of aviation. In the past decade, due to the advances in big data technologies and effective algorithms, the transformative data-driven analysis has begun to play a substantial role in aviation environmental impact analysis. The integration of statistical and machine learning methods in the workflow has made such analysis more efficient and accurate. Through summarizing and classifying the representative works in this intersection area, this survey paper aims to extract prevailing research trends and suggest research opportunities for the future. The methodology overview section presents a comprehensive development process and landscape of statistical and machine learning methods for applied researchers. In the main section, relevant works in the literature are organized into seven application themes: data reduction, efficient computation, predictive modeling, uncertainty quantification, pattern discovery, verification and validation, and infrastructure and tools. Each theme contains background information, in-depth discussion, and a summary of representative works. The paper concludes with the proposal of five future opportunities for this research area. Full article

Non-CO₂ aircraft emissions are responsible for the majority of aviation’s climate impact, however their precise effect is largely dependent on the environmental conditions of the ambient air in which they are released. Investigating the principal causes of this spatio-temporal sensitivity can bolster understanding of aviation-induced climate change, as well as offer potential mitigation solutions that can be implemented in the interim to low carbon flight regimes. This review paper covers the generation of emissions and their characteristic dispersion, air traffic distribution, local and global climate impact, and operational mitigation solutions, all aimed at improving scientific awareness of aviation’s non-CO₂ climate impact. Full article