Environmental prospects in aviation: a study from the Air & Space Academy FC
The environmental context is reviewed: environmental issues (noise, local emissions and air quality, greenhouse gas and global warming), closely linked to technical, economic and social issues, involving multiple interactions between many factors and actors evolve fast, clouding the 2050 horizon with uncertainties. Underlying stakes are growing and matching efforts are needed in order to address them, take adequate measures and implement efficient solutions. In technological and operational fields, efforts are needed, properly balanced among the different criteria, developing cross-disciplinary expertise to better apprehend the environmental issues. The proposed solutions should be based on a thorough assessment of needs, assets and interactions, and their Implementation properly refined and regulated, with a view to ensuring global optimisation, promoting equal treatment and protecting the viability of the sector. Besides, communication, which is sensitive on the environmental aspects of air transport, should be unbiased, coherent and credible. Noise limits are set by a strong, proven framework at international (ICAO standard) and national levels and introducing periodically stiffer limits and refined certification procedures, that stimulated technical progress and significantly reduced noise pollution (perceived noise reduced by 75%, cumulative noise, noise exposure areas reduced). As research is going on and the fleet is renewed, the overall trend should continue, despite the air traffic growth. All in all, the FC projected a total acoustic energy reduction of 15 to 20% between 2010 and 2050. The decoupling of noise and traffic is projected to be achieved even for aircraft equipped with noisier counter- rotating open rotors. Those results do not however take account of local situations and should therefore be placed in context, notably for some potentially critical platforms, where noise will have to be closely monitored, factoring into the analyses and the regulatory framework all elements contributing to acoustic exposure (e.g. land use regulations, noise disturbance generated by an isolated event or exacerbated by repetitive events). The ICAO Balanced Approach, with its four main pillars: noise reduction at source (that requires continued intensive research and development with proper funding), land use planning and management, noise abatement procedures and operational restrictions, is a key principle to be applied everywhere to efficiently manage noise issues around airports, both from an environmental standpoint and an economic perspective. In order to keep the noise reduction advantage provided by technologies and operational procedures, it is crucial that the full set of applicable regulations be enforced, and that undue building construction be prevented. The responsibility for managing and controlling urban development plans should be entrusted to a designated authority, to be set up or reinforced whenever necessary. Local emissions and air quality: the overall situation of nitrogen oxides (NOx ) is similar to that of noise, in that total emissions will be relatively stable between 2010 and 2050, based on FC forecasts for traffic growth and for reductions in fuel consumption and NOx emissions through dedicated technological advances. The corresponding standard is periodically reinforced and the engine certification procedures (ICAO) updated. As is the case for noise, local situations concerning low altitude NOx emissions may need to be monitored, especially where air quality limits can be exceeded under the combined effect of various contributors. Although aviation is a minor offender when compared with surface access transport, facilities and housing, the issue can put a curb on airport development. It is also important to ensure that the results of research and development efforts into NOx emissions meet expectations. Particulate Matter emitted by aircraft/engines are the object of growing concern, due to their impact on air quality and human health. Scientific knowledge remains limited. The role of particulates in cirrus cloud formation at altitude (impacting the greenhouse effect) is still poorly understood. Research on particulate matter should be intensified, and a new specific ICAO standard is envisioned in coming years. The quantities emitted will benefit from reductions in fuel consumption. Nevertheless, their impact, combined with growing emissions will make particulates a major issue in the future. Concerning greenhouse effect and global warming, Aircraft fuel consumption and CO2 emissions have benefited from spectacular improvements in the past, thanks to engine and aircraft performance improvements, in response to growing mobility needs and an exacting market. Industry and ICAO have set ambitious goals for the future: a 1.5% increase in fuel efficiency per year until 2020 (2% for ICAO), carbon neutral growth from 2020, and a halving of total CO2 emissions by 2050 relative to 2005 (industry). The FC has analysed the various factors driving fuel consumption and CO2 emissions between 2010 and 2050, and has forecast the following cumulative gains in fuel consumption per passenger.km: 25% from technology and new aircraft introduced, 37% cumulative when air traffic, operational improvements, increased load factor are factored in, and 47% reduction in CO2 emissions, after adding the benefit of biofuels and various types of carbon compensation effects. Since air traffic is growing at a faster pace than improvements (multiplier slightly higher than 3), total fuel consumption will double during the period, with total CO2 emissions growing by a factor of 1.6. These results are well below the Industry/ICAO goals and the European objective of Flightpath 2050, notably the “carbon neutral growth” from 2020 (including biofuels). The objective of halving total CO2 emissions by 2050 relative to 2005 appears even further out of reach. So, it seems unlikely that technical progress - although it remains a key factor in reducing the sector’s CO2 emissions, implying intensive research efforts - will fill the gap versus the stated objectives. Carbon compensation may contribute to closing in on them, but in order to avoid damaging effects on air transport, it is vital that “compensation” measures be managed on a worldwide basis, ensuring equal access, non- discriminatory treatment, unbiased competition and costs compatible with the sector’s viability. Other forms of carbon compensation may be considered. All means need to be combined, with ICAO playing a major role. Environmental Interdependencies and trade-offs between noise, local and global emissions are inherent to the cross-disciplinary nature of the subject and intrinsic to all phases of design, from initial selection of overall goals to choices of configurations and technologies. They impact propulsion system design, integration and operation. There are many environmental trade-offs, linked to physical principles and factors (e.g. engine internal temperatures, bypass ratio, specific fuel consumption, aerodynamic drag and nacelle acoustic treatment area), with varying impacts on noise, fuel consumption and NOx/CO2 emissions. Such trade-offs concern all new aircraft and depend on the overarching requirements adopted, in close connection with economic performance drivers. They are challenging to analyse and resolve due to the complexity, uncertainties and evolving characteristics of the phenomena involved. As the levels of technical refinement and component efficiency approach ultimate physical limits, each evolution brings some undesirable effects, making arbitration more and more tricky between noise, engine specific fuel consumption (hence CO2) and NOx emissions. The choices of engines and configurations will be crucial in the future (e.g. open rotors vs advanced turbofans) and will need to factor in all effects and requirements.