What steps are being taken to reduce aviation emissions in the longer-term?
The pace of technological change across the industry is increasing. New engine designs are improving fuel efficiency further, while simultaneously reducing NOx emissions. New aircraft designs improve aerodynamics and reduce weight thereby improving fuel efficiency, reducing all pollutants at the same time. New air traffic control technologies, like new aircraft designs, reduce emissions by reducing fuel consumption (the effect on individual pollutants depends on the phase of flight most effected).
And new management strategies like load management planning and code sharing are being used to optimize the entire system’s operation. With regard to engines, there are complex emission interrelationships that make it difficult to modify their design as a mitigation strategy since it forces a tradeoff among individual pollutants as well as between emissions and noise. For example, high-bypass turbofan engines were introduced to reduce noise and improve fuel efficiency. They require higher engine pressure ratios, which increase engine temperatures, and hence generate more NOx. It has only been in the past 25 years that the resulting NOx increase became a concern.
FAA and other stakeholders have recently initiated an effort to better understand and quantify these interrelationships in an environmental design space.” Eventually this will lead to guidelines for setting long term goals and standards that optimize overall environmental performance and avoid unintended consequences.
Aircraft design improvements mostly fall into one of three areas: aerodynamics, weight reduction, and control systems. Continued improvement in all areas is expected in the future45. Some of the technologies in development for aerodynamic improvements include the design of winglets for wing tips, which reduce turbulence and vortex generation by the wings, laminar flow controls or systems for wing surfaces to reduce drag, and improved manufacturing techniques that will produce smoother surfaces.
New and improved metal alloys and composite materials are being developed to reduce aircraft weight while simultaneously improving structural performance. Significant improvement of control systems has come about by replacing mechanical and hydraulic systems with electrical systems, which often reduce system weight while providing more precise control. Improvements of these systems and development of new systems for enhanced flight stability will contribute to improved overall fuel efficiency. Aircraft technology development and capital turnover follow relatively long cycles, which limits the pace of fundamental changes in design.
It takes approximately 10 to 15 years for fleet average fuel efficiency to equal the efficiency of the newest aircraft46. However, the ongoing evolutionary change in technology has realized substantial benefits over time. According to the Intergovernmental Panel on Climate Change, in their report Aviation and the Global Atmosphere47, aircraft fuel efficiency has improved by 75 percent in the past 40 years through improvements in airframe design, engine technology, and rising load factors.
While progress in the near- and mid-terms is expected, the most significant opportunities for emission reduction lie in the future when we can derive benefits from aggressive research goals. FAA, EPA, ICAO, and many other groups have been working to elucidate and characterize the environmental issues for some time while NASA is directing a research program aimed at significantly cutting emissions from aircraft engines.
A comprehensive research program starts with a clear and complete understanding of the effects of aviation on air quality. FAA has developed analytical tools to quantify emissions more accurately, which are used to understand aviation’s contribution to local air quality concerns and global emissions. These tools are developed on a foundation of research that FAA has conducted both independently an in conjunction with airports and other organizations.
The Emissions and Dispersion Modeling System (EDMS) has been developed to quantify emissions from aircraft and other airport emission sources. It is used routinely to assess the impact of airport expansion projects and other operational changes. The System for assessing Aviation’s Global Emissions (SAGE) is being developed to assess the impact of aircraft engine emissions during the whole flight regime, especially climb out and cruise emissions.
The model will be able to develop aviation emission inventories, both for baseline conditions and forecasted technology, and assess operational and market-based measures and improvements. New tools are also being developed to understand and assess the environmental design space, to evaluate interrelationships among all emissions and between emissions and noise due to changes in technology and operational procedures. NASA is the U.S. federal agency responsible for pre-commercial aerospace research, development, and demonstration.
One of the key themes of their research program is to “protect local environmental quality and the global climate by reducing aircraft noise and emissions." Their strategy is to research opportunities to reduce airframe weight and drag, optimize engine systems, and optimize operations at and around airports.
Through this, NASA hopes their research program results in significant or total elimination of aircraft greenhouse gas emissions, minimized impact of emissions on local air quality, and elimination of unnecessary aviation emissions due to operational procedures. The goals of this program are to reduce NOx emissions of future aircraft by 70 percent by 2007, and by 80 percent beyond 2007 using 1996 ICAO standards as a baseline.
They also intend to reduce CO2 emissions of future aircraft by 25 percent and by 50 percent for these same milestones using 2000 state-of-the-art aircraft technology as a baseline.
The primary engine research project to achieve these objectives is the Ultra-Efficient Engine Technology (UEET) project, in NASA’s Vehicle Systems Program. According to NASA, the UEET project will develop and transfer to U.S. industry critical turbine engine technologies that will contribute to enabling a safe, secure, and environmentally friendly air transportation system. This project is currently underway.
FAA, NASA, and Transport Canada have made a major commitment to researching aviation emissions as well as noise through the Center of Excellence for Aircraft Noise and Aviation Emissions Mitigation.
The Center was established in September 2003 to foster break through technical, operational, and workforce capabilities enabling quieter and cleaner aircraft. Achieving research goals will allow the aviation industry to significantly reduce its environmental impact and begin to reduce its total emissions of NOx and CO2.
This takes time, however. As noted earlier it takes 10 to 15 years for fleet average performance to achieve current new technology performance. To go from NASA research to fleet average performance takes 20 to 40 years. Also, concerns have been raised about the likelihood of these goals being met due to budget restrictions. The National Research Council recently published a report, For Greener Skies: Reducing Environmental Impacts of Aviation52, that concluded, while “the goals of the federal research program are admirable and focused on the right issues, the schedule for achieving the goals is unrealistic in view of shrinking research budgets.”
The report went on to call for further federal investment in engine research and technology development. Aviation emissions are being responsibly controlled. Aviation has progressively improved its environmental performance. Fuel economy, which is one strong indicator of environmental performance, has consistently improved. Aircraft engines have gotten more efficient and been designed with environmental performance in mind. Regulatory frameworks have developed to constrain emissions growth from much aviation sources.
And improvements to the efficient operation of the complex aviation network have had a positive effect on the environment. Looking to the future, FAA has a roadmap for continuing to mitigate the environmental impacts of aviation. This includes continuing to improve its understanding of the role of aviation emissions on the environment. FAA is working with industry and other stakeholders to advance the performance of the national and international aviation system as well as to improve individual system components.
And FAA is working in the international arena to evaluate alternative strategies for market-based opportunities for reducing emissions. FAA, together with EPA and NASA, is committed to ensuring aviation emissions do not pose health concerns for our citizens or restrain aviation’s mobility and economic benefits enjoyed by society. It will take consistent, coordinated effort and continuing success in technology research and development to achieve these goals.
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