Noise is one of the most significant environmental impacts of aviation. Although noise is present around virtually every airport in the country, the problem is greatest near busy commercial airports served by large jet aircraft. According to FAA, the retirement of older, louder aircraft and ground-based noise-mitigation efforts over the past 35 years have reduced by over 90 percent the number of people affected by significant aviation noise levels—defined as a 65-decibel day night level (DNL 65 dB) or greater—despite nationwide increases in population and air traffic. FAA’s estimates indicate that from 2000 to 2006 alone, the number of people affected by these noise levels dropped by more than a third, from about 780,000 to about 500,000. Nevertheless, these half million people are still exposed to significant aviation noise levels, and as communities expand near airports just outside the highly exposed areas and as air traffic increases, millions more are affected by lower levels of aviation noise. Changes in aircraft flight paths can also affect communities’ exposure to aviation noise, redirecting air traffic over some communities that were not previously exposed and diverting it from others. Both jet aircraft engines and jet airframes produce aviation noise during aircraft operations, particularly during takeoffs and landings. Moreover, certain types of aircraft contribute disproportionately to the level of noise around airports. In our 2000 report on environmental concerns and challenges for airports, we reported that the primary issue of concern identified by officials of the nation’s 50 busiest airports was the noise generated by older jet aircraft. With the implementation of technologies to reduce aircraft engine noise, efforts to reduce noise from airframes will become more important. As technologies for reducing aviation noise have advanced (see our discussion of some of these advances in the next section of this testimony), regulatory standards for jet aircraft noise have become more stringent. The Airport Noise and Capacity Act of 1990 authorized the Secretary of Transportation to reduce aviation noise through a program to phase out older, noisier aircraft – known as Stage 2 aircraft— by December 31, 1999. Aircraft owners could either retire Stage 2 aircraft weighing over 75,000 pounds or modify them with hushkits to sufficiently muffle the noise they generated to meet Stage 3 standards. FAA had adopted the Stage 3 standards in 1977, the year they were established by the International Civil Aviation Organization (ICAO), and all aircraft designed after that time were required to meet the Stage 3 standards, but previously certified aircraft designs were grandfathered until the 1990 act required that they be retired or modified. However, the act exempted aircraft weighing less than 75,000 pounds, a category that includes older business class jets. Stage 2 aircraft that weigh less than 75,000 pounds and Stage 3 aircraft that have been recertified as such after being modified with hushkits are in compliance with current standards, although these aircraft tend to be louder than new aircraft in the same weight range. Bills pending in both the House and the Senate would require, with certain exceptions, that all existing aircraft meet Stage 3 standards, including those aircraft under 75,000 pounds that are currently exempted. In addition, in July 2005, FAA issued a Federal Aviation Regulation requiring that all new jet aircraft designs be subject to the current, more stringent ICAO noise standards, known as Stage 4. Specifically, any new aircraft whose design was submitted to FAA for approval on or after January 1, 2006, must meet these standards, which are based on the Chapter 4 standards adopted by ICAO in 2001. The Stage 4 standards are 10 decibels lower on a cumulative basis than the Stage 3 standards and represent a significant reduction in noise. Since 2001, substantial progress has been made in retiring older, noisier aircraft. According to FAA, there has been a reduction of about 70 percent in the number of registered aircraft that have been modified with hushkits—mainly Boeing 727s and DC-9s. Today, there are 498 registered hushkitted aircraft, which make up about 8 percent of the U.S. commercial aircraft fleet. The replacement of these older aircraft with new, quieter aircraft has been the most important factor in decreasing noise around airports since the significant noise reductions achieved through the phaseout of Stage 2 commercial aircraft, according to FAA. Figure 1 indicates that the number of people exposed to significant noise levels has decreased even as the number of people flying has increased. Decisions that allow communities to expand near airports may expose residences, schools, hospitals, and other uses to aviation noise. Such decisions are made primarily by local governments, but airports, which cannot control development in the communities that surround them, may nevertheless be held accountable by these communities for the effects of aviation noise. Although the areas around airports exposed to significant noise levels (DNL 65 dB or greater), known as noise contours (see fig. 2), have shrunk with the retirement of older aircraft, the incompatible use of land around airports remains a problem in dealing with the effects of aviation noise. Some stakeholders have said that the gains that have been made in noise attenuation through regulation and technology are being eroded or threatened by incompatible land use. FAA set the DNL 65 dB standard that is used to measure noise contours. This standard reflects the level of noise exposure over time that FAA has determined annoys people by interfering with normal activities such as sleep, relaxation, school, and business operations. FAA has also issued guidelines that identify land uses that would not be compatible with the noise generated by a nearby airport’s operations, as well as land uses that could successfully be located close to an airport without interfering with their activity. Despite this guidance, however, strong pressure exists to develop residential areas around heavily used airports, and despite the steady decline in the number of people exposed to significant noise levels (DNL 65 dB and above), large numbers of people are still exposed to at least some noise around airports. And for FAA, population increases in areas around airports that are exposed to even moderate amounts of aviation noise pose a challenge because, given individuals’ varying sensitivity to noise, even comparatively low levels of exposure can generate community concerns. Population growth near airports also creates challenges for airports when planning expansion projects to meet the growing demand for air travel. Any efforts to limit development have implications for the tax base of local communities. As a result, as FAA noted in a 2004 report to Congress on aviation and the environment, there is a disconnect between federal aviation policy and local land-use decision-making. Until recently, evidence about trends in land use incompatible with airport activity was mostly anecdotal, but some empirical research is now available. For example research sponsored by FAA and NASA shows that for 92 commercial airports, between 1990 and 2000, “the effectiveness of existing federal land-use guidelines on reducing total noise exposure and deterring residential development inside the DNL 65 dB contours is mixed.” Moreover, according to the research, “land-use planning has done little to address the increasing population aggregation on lands near existing noise footprints.” Furthermore, according to FAA, incompatible land use is emerging as a problem around reliever airports, which predominantly service general aviation traffic that would otherwise go to nearby busy airports. These airports are located in quieter suburban and rural areas where aviation noise is more noticeable. Local governments with jurisdiction over land- use planning and development continue to permit building near airports, where developable land is comparatively plentiful. As a result, communities that did not exist when some airports were built are now opposing increases in aircraft operations and expansion at these airports. The air traffic environment for the nation’s airspace was designed and implemented in the 1960s and has undergone only minor changes over the years. However, the use of the airspace has changed significantly, with higher overall air traffic volumes and greater use of smaller and regional jet aircraft. As discussed later in this statement, FAA’s airspace redesign initiatives have the potential to improve safety and efficiency by allowing the use of new arrival and departure procedures that can reduce the impact of noise and emissions on nearby communities. At the same time, though, they have led to concerns about aviation noise in some communities that were not previously exposed to it. Airspace redesign projects usually involve changes in aircraft arrival and departure routes from airports. These changes may result in exposing some communities to less noise and others to more noise. FAA has completed over 30 airspace redesign projects, including projects around major airports such as those serving Las Vegas, Dallas-Fort Worth, Minneapolis, and Boston. According to FAA, between 2002 and 2007, airspace redesign projects have produced almost $700 million in customer benefits from reduced delays, more efficient routing, and reduced restrictions attributable to a more balanced air traffic control workload. Until recently, most airspace redesign projects have involved changes in flight paths above 10,000 feet and have therefore not had a significant impact on noise levels in communities near airports. However, FAA has approved the most ambitious airspace redesign project to date, which involves flight path changes in the New York/New Jersey/Philadelphia airspace, including changes at levels below 10,000 feet. According to FAA, this airspace is some of the most complex and congested anywhere in the world, with about one third of the nation’s commercial air traffic passing through it. Delays and congestion in this airspace or at area airports tend to ripple throughout the system. Airspace redesign projects have the potential to alleviate some of these problems at this critical chokepoint in the national airspace system. Because the airspace redesign for the New York/New Jersey/Philadelphia area will make changes to arrival and departure routes, the noise contours in the area will also change, exposing some communities to less noise and others to more. According to FAA’s analysis of the effect of the redesign, fewer people would be exposed to moderate to significant noise levels than is currently the case, but some people who live under the new flight paths would be exposed to higher though moderate levels of noise.