National Academies Press: OpenBook
« Previous: Front Matter
Suggested Citation:"Executive Summary." National Research Council. 2002. For Greener Skies: Reducing Environmental Impacts of Aviation. Washington, DC: The National Academies Press. doi: 10.17226/10353.

Executive Summary

Providing rapid and safe transportation across the nation and around the world, contemporary aviation contributes significantly to the national economic vitality and to the business and pleasure of millions of citizens. In addition, the manufacture of aviation products provides substantial direct economic benefits as a source of jobs in the United States, and as the largest positive contributor to the balance of trade in goods. But large amounts of energy are required to propel modern jet transports, and thus both noise and emission of combustion products are a consequence of powered flight.

Scientific and technological progress in the 50 years since the advent of turbine engines has produced dramatic reductions in their noise and emissions. But even though individual airplanes are quieter and cleaner, the rapidly increasing demand for aviation services has mandated more airplanes and more flights, and so the total environmental consequences have increased and become more obvious. At the same time, the awareness of environmental issues and the political pressures to resolve them have also increased dramatically. Aircraft operations and the construction of new facilities are now seriously constrained by environmental restrictions. Indeed, the U.S. air transportation system is caught today between two powerful but conflicting expectations—the first for more services, the second for decreased environmental impact. The presumably short-term reduction in demand for air travel in the aftermath of the September 2001 attacks on the World Trade Center and the Pentagon does not resolve the issues addressed by this report. It merely provides an opportunity for advanced technology to mitigate existing environmental impacts before the inevitable resumption of demand growth makes them worse.

The technical challenges are too large and regulatory and economic incentives too small for industry acting alone to eliminate the environmental effects of the growth in air travel and the demand for aviation services. The federal government has long accepted part of the responsibility for the advance of aviation and for reducing its environmental impact. But today the federal research efforts are not commensurate with the intensifying severity of the problem. 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 and increasing isolation from industry and academia. As research budgets are cut, a higher percentage of the remaining funds are spent to support in-house work at National Aeronautics and Space Administration (NASA) research centers. This causes an even larger reduction in the percentage of research funding left for research and technology development by universities and industry.

Most of the federal funding available for addressing issues associated with aircraft noise and emissions is used for noise abatement at selected airports, primarily by soundproofing buildings in high-noise areas outside airport boundaries or purchasing land to extend airport boundaries to encompass high-noise areas. Relatively little is spent on research and technology to control noise or emissions at the source. This funding scheme is a consequence of the way funds are raised and appropriated. Most of the funds appropriated for these purposes are raised from taxes on airline tickets, primarily for the purpose of subsidizing airport improvements or noise abatement measures in homes and other buildings near airports, and they are administered by the Federal Aviation Administration (FAA). Primary responsibilities for developing advanced aircraft technologies for reducing noise at the source, however, are assigned to NASA, which has no independent sources of funding to support aeronautics research.

Finding—Vigorous Action Required. Environmental concerns will increasingly limit the growth of air transportation in the 21st century unless vigorous action is taken to augment current research and technology related to the environmental impacts of aviation.

Suggested Citation:"Executive Summary." National Research Council. 2002. For Greener Skies: Reducing Environmental Impacts of Aviation. Washington, DC: The National Academies Press. doi: 10.17226/10353.


Aviation noise reduces property values, contributes to delays in expanding airport facilities, and prompts operational restrictions on existing runways that increase congestion, leading to travel delays, high ticket prices, and high airline capital and operating costs. The situation would be much worse, however, if not for past investments in advanced technology. Over the past 30 years, the number of people in the United States affected by noise (i.e., the number of people who experience a day-night average sound level of 55 dB) has been reduced by a factor of 15, and the number of people affected by noise has been reduced by a factor of 100, as measured per unit of service provided (revenue-passenger-kilometer).

The most significant limitations to further reductions in the effect of aviation noise (or emissions) include growth in demand, long lead times for technology development and adoption, long lifetimes of aircraft in the fleet, high development and capital costs in aerospace, high residual value of the existing fleet, and low levels of research and development funding. While spending huge sums on local palliatives such as soundproofing buildings, the federal government reduced funding for the research that would quiet the entire fleet in the decades ahead. For example, the noise reduction element of NASA’s Advanced Subsonic Technology Program was an excellent model for government-industry collaborations involved in commercialization of advanced technology. This program has been terminated, however, and replaced with a new program with fewer resources and less industry involvement.

In 2001, the FAA expended about $500 million on noise abatement, while the FAA and NASA together expended less than $60 million on noise and emissions research. The need to place more emphasis on research was noted in the fiscal year 2002 appropriations for the Department of Transportation, which directed that $20 million from the Airport and Airway Trust Fund be used to accelerate the introduction of quieter aircraft technologies. These funds were provided to the FAA, with the expectation that it would “work directly with” NASA “to advance aircraft engine noise research,” and about $14 million is being used to augment NASA research funding in this area. Congress took this action because community opposition to aircraft noise is preventing the necessary expansion of some airports and because “aircraft noise results in millions of federal dollars being spent each year on mitigation measures, diverting funds which could be applied to capacity enhancement or safety projects” (Congress, 2001). The committee endorses this action as a first step in reducing the imbalance in the allocation of aircraft noise funding. Much more needs to be done.

Most federal research on noise reduction is performed or managed by NASA. NASA’s goals for noise reduction are to cut the perceived noise of future subsonic aircraft in half (i.e., by 10 dB) between 1997 and 2007 and to cut the noise in half again by 2022 (NASA, 2002). Achieving these goals will be very difficult—and will require a rate of technological advance that is greater than the historical record would predict (see Figure ES-1). Furthermore, even in the unlikely event that these aggressive goals are achieved, noise may continue to constrain the U.S. air transportation system, in large part because communities near airports are placing greater emphasis on a low-noise environment as part of their quality of life.

The Federal Interagency Committee for Aircraft Noise facilitates information sharing among federal agencies interested in aircraft noise. This committee could be strengthened and made more effective if agencies appointed personnel who have budgetary authority within their home organizations as members of the committee.

Recommendation—Balanced Allocation of Funds. Federal expenditures to reduce noise should be reallocated to shift some funds from local abatement, which provides near-term relief for affected communities, to research and technology that will ultimately reduce the total noise produced by aviation. Currently, much more funding is devoted to local abatement than to research and technology. Also, to avoid raising unrealistic expectations, the federal government should realign research goals with funding allocations either by relaxing the goals or, preferably, by reallocating some noise abatement funds to research and technology.

Recommendation—Technology Maturity and Scope. NASA and other agencies should sustain the most attractive noise reduction research to a technology readiness level high enough (i.e., technology readiness level 6, as defined by NASA) to reduce the technical risk and make it worthwhile for industry to complete development and deploy new technologies in commercial products, even if this occurs at the expense of stopping other research at lower technology readiness levels. NASA and the FAA, in collaboration with other stakeholders (e.g., manufacturers, airlines, airport authorities, local governments, and nongovernmental organizations), should also support research to accomplish the following:

  • Establish more clearly the connection between noise and capacity constraints.

  • Develop clear metrics for assessing the effectiveness of NASA and FAA noise-modeling efforts.

  • Implement a strategic plan for improving noise models based upon the metrics.

  • Harmonize U.S. noise reduction research with similar European research.

Recommendation—Interagency Coordination. Interagency coordination on aircraft noise research should be enhanced by ensuring that the members of the Federal Interagency Committee for Aircraft Noise have budget authority

Suggested Citation:"Executive Summary." National Research Council. 2002. For Greener Skies: Reducing Environmental Impacts of Aviation. Washington, DC: The National Academies Press. doi: 10.17226/10353.

FIGURE ES-1 Historical trends in aircraft noise compared with NASA’s noise goals. SOURCE: Lukachko and Waitz, 2001.

within their own organizations to implement a coordinated strategy for reducing aviation noise.


The aviation industry is growing, and the use of aviation fuel is increasing at a rate comparable to that for other uses of fossil fuels. Between 1992 and 1999, the United States increased its consumption of natural gas (10 percent), petroleum (12 percent), and coal (13 percent). The consumption of jet petroleum increased by 14 percent, and the consumption of petroleum products by the entire transportation industry increased by 15 percent. Jet petroleum represents 3 percent of the total U.S. energy consumption and some 10 percent of petroleum consumption.

All other factors being equal, the amount of emissions produced by aircraft is essentially proportional to fuel consumption, which is proportional to flight activity. One option for reducing emissions is advanced technology, and during the past 50 years major advances in aircraft turbine engines have been realized as a result of extensive efforts by engine manufacturers and cognizant government agencies. In the United States, NASA has been a significant contributor to these sustained advances. From the outset, the goals of these efforts have included improved engine reliability, durability, and fuel efficiency, all of which have significant economic implications for the airlines. Dramatic progress has been made in all three of these crucial aspects, but the increased efficiencies of individual airplanes are not sufficient to decrease the total emissions of a global fleet growing in response to accelerating demand. For newly designed aircraft, advanced technology could reduce fuel consumption per revenue-passenger-kilometer by about 1 percent per year for the next 15 to 20 years. During the same time, however, the demand for global air transportation services is expected to increase by 3 to 5 percent per year (see Figure ES-2).1 An aggressive, broad-based research program that includes technology to improve propulsion systems, the airframe, and operational systems and procedures could significantly close this gap, but existing allocations of research funds within NASA and the FAA are insufficient to support such a program.

Funding allocated to achieve NASA’s goals for reducing carbon dioxide (CO2) and oxides of nitrogen (NOx) is insufficient to reach the specified milestones on time. Research to reduce NOx and improve engine efficiency, although part of the NASA Ultra Efficient Engine Technology Program, has been significantly reduced in scope in the past few years to


The September 11, 2001, attacks on New York City and Washington, D.C., will shift plots of future growth in air travel to later years. However, lacking data on how much of an adjustment to make, the committee is relying on historical projections which reflect trends that are expected to resume in the long term.

Suggested Citation:"Executive Summary." National Research Council. 2002. For Greener Skies: Reducing Environmental Impacts of Aviation. Washington, DC: The National Academies Press. doi: 10.17226/10353.

FIGURE ES-2 Decadal trends for demand, efficiency, and fuel usage. Dashed portions of curves are projections. SOURCE: Lukachko and Waitz, 2001.

accommodate NASA’s shrinking aeronautics research budget. These reductions jeopardize achievement of program goals and do not appear to carry the research far enough so that results can be readily adopted by industry.

Additional scientific research is also needed to set appropriate regulatory standards and to frame technology development goals and plans. Research is needed to (1) clarify the extent to which aircraft effluents introduce hazardous air pollutants into the airport environment; (2) examine the formation of particulates and aerosols in aircraft engines and exhaust plumes during idle, taxi, and flight; and (3) quantify the effects of aircraft emissions on radiative forcing in the atmosphere, the formation and persistence of cirrus clouds, and climate change globally and regionally. Even though large uncertainties remain regarding aviation’s effects on the atmosphere, research budgets for examining this issue have been cut by two-thirds in recent years.

Recommendation—Eliminating Uncertainties. NASA should support additional research on the environmental effects of aviation to ensure that technology goals are appropriate and to validate that regulatory standards will effectively limit potential environmental and public health effects of aircraft emissions, while eliminating uncertainties that could lead to unnecessarily strict regulations.

Recommendation—Research on Global, Regional, and Local Emissions. NASA should continue to take the lead in supporting federal research to investigate the relationships among aircraft emissions (CO2, water vapor, NOx, SOx, aerosols, particulates, unburned hydrocarbons, and other hazardous air pollutants) in the stratosphere, troposphere, and near the ground, and the resulting changes in cirrus clouds, ozone, climate, and air quality (globally, regionally, and locally, as appropriate). Other agencies interested in aircraft or the environment should also support basic research related to these programmatic goals.


The conflict between the increased demand for aviation services and more stringent environmental constraints mandates a careful examination of the associated economic and political realities and policies. The government has responsibilities for fostering aviation as a contributor to the national infrastructure, for defining realistic environmental goals, and for developing environmental policies and regulations to meet such goals. To ensure that the goals and policies are appropriate, the full extent of environmental costs, the economic benefits of reducing noise and emissions, and the potential of financial incentives for owners

Suggested Citation:"Executive Summary." National Research Council. 2002. For Greener Skies: Reducing Environmental Impacts of Aviation. Washington, DC: The National Academies Press. doi: 10.17226/10353.

and operators to reduce environmental impacts should all be considered.

Manufacturers attempt to produce new aircraft that cost less and are more reliable than their predecessors. At the same time, government intervention is important to encourage manufacturers, operators, and consumers of aviation services to reduce the environmental consequences of aircraft operations, which will sometimes increase costs. There are international implications, too, because many domestic rules are written in accordance with multinational agreements established by the International Civil Aviation Organization; also, other nations sometimes unilaterally establish rules that affect the operations and competitiveness of U.S. aircraft or airlines.

Thus, the government is an active participant in promoting aviation and in ensuring the environmental compatibility of aviation, both by assisting in the development of new technologies and in regulating the noise and emissions that attend aircraft operations. An important question is whether the current policy framework is well equipped to satisfy both environmental goals and the public’s demand for aviation services. One way to consider this question is to examine the full costs for consumers, operators, and manufacturers of doing business in competitive markets, including the costs related to environmental compatibility and the consequences of inadequate facilities and capacity. Knowing the full costs of operations, the likely costs and consequences of technological intervention, and the costs of the potential solutions (technological and regulatory) would allow policy alternatives to be ranked and better policy decisions to be made.

An associated policy issue is whether it is possible to create marketplace incentives for industry to develop and deploy environmental technologies that go beyond regulatory requirements. For example, a few major European airports have implemented landing fees that reward operators who use ultralow-NOx combustors while penalizing operators using standard combustors. The cost differential does not appear to be a sufficient financial incentive to most international air carriers, for whom operations at these airports represent a very small fraction of their total operations. As a result, advanced combustors, some of which can reduce NOx as much as 60 percent below international standards, have a limited market because (1) they cost more than simpler combustors (that reduce NOx to about 35 percent below current standards) and (2) they provide no economic benefits to offset their higher cost.

Recommendation—Considering All Costs and Benefits. To support the formulation of environmental goals and air transportation policies, government and industry should invest in comprehensive interdisciplinary studies that quantify the marginal costs of environmental protection policies, the full economic benefits of providing transportation services while reducing the costs (in terms of noise, emissions, and congestion), and the potential of financial incentives to encourage the development and use of equipment that goes beyond regulatory standards.


Strong action is essential to avert a paralyzing collision between the growth of aviation and increasing concerns about the quality of the environment. A national strategy and a federal plan for action are much needed. Two significant issues must be faced:

  1. Technology lead times. With service lives of 25 to 40 years for individual models of commercial aircraft, it can take decades for a major technological improvement to appear in a majority of the commercial fleet. NASA, the FAA, and industry could reduce lead times by collaborating in the development of mature, proven technology that the FAA is willing to certify, airlines are willing to purchase, and manufacturers are willing to develop.

  2. Economic incentives. The government and the public must recognize the need for economic incentives for manufacturers and airlines to embrace technologies that minimize environmental impacts. Although passengers are unlikely to pay more to ride on an airplane with lower takeoff or approach noise, they may be willing to pay more to fly in a newer airplane that offers other advantages in addition to reduced environmental impacts. More certain, however, is the ability of the government to establish economic incentives for using advanced environmental technologies. Possibilities include tax advantages for operators of “greener” airplanes and direct grants for environmental innovation or leadership.

Finding—Status of Environmental Research. Research seeking to mitigate the environmental impacts of aviation is important to national and global well-being, but present efforts are operating with ambitious goals, unrealistic time-tables for meeting them, and few and diminishing resources.

The ultimate goals for environmental research related to aviation remain uncertain for several reasons:

  • The actual effects of aviation on the environment are uncertain.

  • Aircraft emissions are only a small contributor to global atmospheric issues.

  • Solutions may involve revolutionary changes in aircraft design.

  • The noise levels that will ultimately prove acceptable to the general public (especially to people living near airports) and eliminate noise as a critical limitation on the growth of air traffic are unknown.

Suggested Citation:"Executive Summary." National Research Council. 2002. For Greener Skies: Reducing Environmental Impacts of Aviation. Washington, DC: The National Academies Press. doi: 10.17226/10353.

Recommendation—Additional Research. To reduce conflicts between the growth of aviation and environmental stewardship, NASA, the FAA, and the Environmental Protection Agency (EPA) should augment existing research by developing specific programs aimed at the following topics:

  • determining which substances identified by the EPA as hazardous air pollutants are contained in aircraft emissions and need to be further reduced

  • understanding and predicting atmospheric response to aircraft emissions as a function of time on local, regional, and global spatial scales

  • exploring the suitability of alternate sources of energy for application to aviation, taking full account of safety and operational constraints

Recommendation—Taking Advantage of Experience. The following lessons, learned since the advent of jet-powered aircraft, should be used to formulate and evaluate strategies for reducing the environmental effects of aviation:

  • Success is not easy—it requires government support and federal leadership in research and development of new technology. Establishing a strong partnership involving federal, state, industry, and university programs is essential to progress.

  • Changes in the impact of aviation on the environment occur on the scale of decades as fleets evolve; technological success in reducing adverse impacts occurs on the same or longer scales.

  • The formulation of technological strategies to reduce the environmental impacts of aviation is hampered by significant uncertainties about (1) long-term effects of aviation on the atmosphere, (2) economic factors associated with aircraft noise and emissions, and (3) the level of noise and emissions that ultimately will prove to be acceptable to airport communities and the general public, nationally and internationally.

With a final recommendation, the Committee on Aeronautics Research and Technology for Environmental Compatibility calls for leadership by the federal government to ensure the growth of an environmentally compatible national aviation capability in the 21st century:

Recommendation—The Federal Responsibility. The U.S. government should carry out its responsibilities for mitigating the environmental effects of aircraft noise and emissions with a balanced approach that includes interagency cooperation and investing in research and technology development in close collaboration with the private sector and university researchers. Success requires commitment and leadership at the highest level as well as a national strategy and plan that does the following:

  • coordinates agency research and technology goals, budgets, and expenditures with national environmental goals and international standards endorsed by the federal government

  • periodically reassesses environmental goals and related research programs to ensure that they reflect current understandings of the impact of specific aircraft emissions on the environment and human health

  • takes advantage of the unique expertise of both government and industry personnel and reverses the current trend of lessening industry involvement in NASA-sponsored environmental research and technology development

  • reallocates funds in accordance with long-term goals, shifting some resources from short-term mitigation in localized areas to the development of engine, airframe, and operational/air traffic control technologies that will lead to aircraft that are quieter, operate more efficiently, and produce fewer harmful emissions per revenue-passenger-kilometer

  • supports international assessments of the effects of aircraft emissions and the costs and benefits of various alternatives for limiting emissions

  • expedites deployment of new technologies by maturing them to a high technology readiness level (i.e., technology readiness level 6, as defined by NASA) and providing incentives for manufacturers to include them in commercial products and for users to purchase those products

Aviation is critically important to individuals, the economy, and the nation, yet the U.S. aviation industry has struggled with serious capacity issues, conflicting expectations regarding delays and environmental impacts, and long-standing federal policies on the expenditure of funds that limit support for the very research that is the key to long-term success. Vigorous federal leadership is essential to overcome funding restrictions and political issues and ensure that research and technology development proceeds as rapidly as is scientifically possible.


Congress. 2001. Conference Report on H.R. 2299, Department of Transportation and Related Agencies Appropriations Act, 2002. Congressional Record, November 29, 2001. Vol. 147, No. 163. Washington, D.C.: U.S. Government Printing Office. Available online at <>. January 15, 2002.

Lukachko, S., and I. Waitz. 2001. Environmental compatibility of aviation graphs. Cambridge, Mass.: Massachusetts Institute of Technology Gas Turbine Laboratory.

NASA (National Aeronautics and Space Administration). 2002. Technology Goals and Objectives. Office of Aerospace Technology. Available online at <>.

Suggested Citation:"Executive Summary." National Research Council. 2002. For Greener Skies: Reducing Environmental Impacts of Aviation. Washington, DC: The National Academies Press. doi: 10.17226/10353.
Page 1
Suggested Citation:"Executive Summary." National Research Council. 2002. For Greener Skies: Reducing Environmental Impacts of Aviation. Washington, DC: The National Academies Press. doi: 10.17226/10353.
Page 2
Suggested Citation:"Executive Summary." National Research Council. 2002. For Greener Skies: Reducing Environmental Impacts of Aviation. Washington, DC: The National Academies Press. doi: 10.17226/10353.
Page 3
Suggested Citation:"Executive Summary." National Research Council. 2002. For Greener Skies: Reducing Environmental Impacts of Aviation. Washington, DC: The National Academies Press. doi: 10.17226/10353.
Page 4
Suggested Citation:"Executive Summary." National Research Council. 2002. For Greener Skies: Reducing Environmental Impacts of Aviation. Washington, DC: The National Academies Press. doi: 10.17226/10353.
Page 5
Suggested Citation:"Executive Summary." National Research Council. 2002. For Greener Skies: Reducing Environmental Impacts of Aviation. Washington, DC: The National Academies Press. doi: 10.17226/10353.
Page 6
Next: 1. Contemporary Realities of Aviation, the Economy, and the Environment »
For Greener Skies: Reducing Environmental Impacts of Aviation Get This Book
 For Greener Skies: Reducing Environmental Impacts of Aviation
Buy Paperback | $47.00 Buy Ebook | $37.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

Each new generation of commercial aircraft produces less noise and fewer emissions per passenger-kilometer (or ton-kilometer of cargo) than the previous generation. However, the demand for air transportation services grows so quickly that total aircraft noise and emissions continue to increase. Meanwhile, federal, state, and local noise and air quality standards in the United States and overseas have become more stringent. It is becoming more difficult to reconcile public demand for inexpensive, easily accessible air transportation services with concurrent desires to reduce noise, improve local air quality, and protect the global environment against climate change and depletion of stratospheric ozone. This situation calls for federal leadership and strong action from industry and government.

U.S. government, industry, and universities conduct research and develop technology that could help reduce aircraft noise and emissions-but only if the results are used to improve operational systems or standards. For example, the (now terminated) Advanced Subsonic Technology Program of the National Aeronautics and Space Administration (NASA) generally brought new technology only to the point where a system, subsystem model, or prototype was demonstrated or could be validated in a relevant environment. Completing the maturation process-by fielding affordable, proven, commercially available systems for installation on new or modified aircraft-was left to industry and generally took place only if industry had an economic or regulatory incentive to make the necessary investment. In response to this situation, the Federal Aviation Administration, NASA, and the Environmental Protection Agency, asked the Aeronautics and Space Engineering Board of the National Research Council to recommend research strategies and approaches that would further efforts to mitigate the environmental effects (i.e., noise and emissions) of aviation. The statement of task required the Committee on Aeronautics Research and Technology for Environmental Compatibility to assess whether existing research policies and programs are likely to foster the technological improvements needed to ensure that environmental constraints do not become a significant barrier to growth of the aviation sector.


  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook,'s online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

    « Back Next »
  6. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  7. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  8. ×

    View our suggested citation for this chapter.

    « Back Next »
  9. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!