Since the late 1950s, noise from aircraft and other airport operations has generated controversy within many surrounding communities and can be a constraint on airport development and aircraft operations. As we have previously reported, noise is one of the top environmental concerns at airports.such as cities, counties, or port authorities, which have primary responsibility for addressing community concerns about noise. The federal government has a long history of helping airports address noise concerns by, for example, defining how airport noise is measured; providing a framework for assessing the impact of noise and for airports to plan noise mitigation projects; and funding eligible noise mitigation projects. Within this context, airports may undertake a range of noise mitigation projects. The federal government has also required the use of Most airports are owned and operated by public authorities, quieter aircraft technologies. The Aviation Noise and Capacity Act of 1990 required that all commercial jets at civilian airports switch to Stage-3 aircraft by the year 2000. Airlines phased out the loudest aircraft over time, and by 2000, the U.S. commercial fleet was composed of quieter aircraft than in the 1990s. Pub. L. No. 96-193, §104, 94 Stat. 51 (1980). incompatible land uses and estimates of the population residing within those contours), and the location of noise sensitive public buildings, such as schools, as defined by FAA regulations. For example, residential development within the DNL 65+ dB contour is deemed incompatible, whereas commercial and manufacturing development is not because of the different impacts of noise on people. The NCP documents the noise mitigation projects the airport proposes to implement and is submitted to FAA for review and approval. The airport may offer mitigation measures within incompatible land use areas that meet other eligibility criteria. For example, a residence located within a DNL 65+ dB area that also has interior noise levels above DNL 45 dB may receive noise insulation. Airport participation in the Part 150 process is voluntary. The typical level of noise in a suburban residential neighborhood that is not near an airport is about DNL 50 dB and an urban residential area is about DNL 60 dB. FAA administers two programs that fund airports’ capital development projects, including noise-related projects. With the creation of the AIP in 1982, FAA had a source of funds to provide grants to airports for noise mitigation projects. Congress reserved a set-aside specifically for noise projects that is currently funded at no more than $300 million per year, but has also expanded over time to include other types of environmental projects including water projects at airports undertaken as a result of an environmental record of decision for an airport development project and certain types of air quality projects. Capital projects in approved NCPs that meet AIP criteria are eligible for AIP grants. Further, airports can be awarded AIP noise grants for some types of noise mitigation projects without an NCP. First, in 2003, AIP noise grant eligibility was temporarily expanded by permitting FAA to provide grants to state and local governments for land use compatibility planning and noise mitigation projects around large and medium hub airports if the airport had not submitted a Part 150 study or had not updated its NCP for more than 10 Second, the National Environmental Policy Act of 1969 (NEPA), years.as amended, requires federal agencies to examine the potential impacts associated with a proposed federal action, including potential noise impacts. As a result, airport development proposals, such as adding new runways or otherwise expanding capacity, must be reviewed for the potential environmental effects as fully as technical, economic and other considerations. Likewise, operational changes, such as changes in flight paths, may trigger a similar review process, depending on the extent of the likely noise impact. These reviews may require airports to prepare an environmental assessment or may require the FAA to prepare an environmental impact statement which could, in turn, lead to a noise mitigation project that is eligible for AIP funding. Airports must match AIP grants to varying degrees, depending on an airport’s size. The second FAA funding program for noise mitigation projects is the Passenger Facility Charge (PFC) program. This program allows publicly operated airports to charge passengers a fee and retain these fees for their use on FAA-approved projects, including those that reduce noise. Project eligibility criteria for the PFC and AIP programs are largely the same, although an NCP is not required to use PFC funds for noise mitigation projects. PFC funds can be used to match AIP grants. There are a variety of projects and actions to mitigate and reduce airport noise that airports may use, some of which are eligible for AIP grants. See figure 1. The number of people exposed to airport noise has been steadily declining for several decades, according to FAA. FAA uses a model, called Model for Assessing Global Exposure from Noise of Transport Airplanes (MAGENTA), to calculate a high-level national estimate of the population exposed to different levels of airport noise. MAGENTA uses, among other factors, airport-level information about the number of aircraft operations, types of aircraft, flight paths, and census data for communities near airports (see sidebar). Individual airports may have, through Part 150 studies or through studies undertaken for NEPA compliance, for example, more precise estimates. FAA estimates that approximately 7 million people lived in areas exposed to significant airport noise—DNL 65 dB or higher—in 1975. Through the 1980s and 1990s, this exposure declined to less than a million by the year 2000. FAA estimates that about 309,000 people currently live in areas at or above DNL 65 dB. FAA estimates also show declines in the populations exposed to non- significant airport noise (i.e., below DNL 65 dB). For example, FAA estimates that between 2000 and 2010 the number of people residing in areas with DNL 60 to 65 dB decreased from about 3 million to 1.5 million (see fig. 2). The downward trend in noise exposure has held relatively steady despite overall increases in air traffic. For example, total U.S. operations—including arrivals and departures—went up from approximately 17.4 million in 2000 to 20.8 million in 2011, though some locations have seen declines. FAA’s model is intended to determine the population living within geographic areas exposed to airport noise, regardless of whether the houses or apartments have been sound insulated using AIP, PFC, or other funds. Consequently, some percentage of the population that FAA estimates is exposed to DNL 65 dB or higher lives in structures that have benefited from noise insulation. There are no readily available data to determine this percentage. Thus, FAA’s model cannot be used to specifically assess the results of AIP grants. As with the shrinkage in the populations living in noise-exposed areas, the geographic areas exposed to significant noise around airports have also generally been shrinking based on multiple recent assessments of DNL 65 dB noise contours that we, FAA officials, and others have conducted. Likewise, FAA and airport officials, as well as industry representatives with whom we spoke generally agreed that the DNL 65 dB noise contours around airports have been shrinking. We did not perform an overall assessment of the extent of this change because noise exposure maps are updated at different times at the discretion of individual airports. At all seven of the airports we examined—including two airports that have recently added runways—noise contours have shrunk overall, according to airport officials or our assessments of noise exposure maps for these airports. For example, at Atlanta-Hartsfield airport, the DNL 65 dB contour has become smaller since the 1980s despite a tripling of airport operations. Likewise, at Seattle-Tacoma International airport, noise contours are substantially smaller today than in the past. Specifically, the DNL 65 dB contour decreased in area almost 60 percent, from approximately 14 to 6 square miles, from 1998 to 2009. However, while noise exposed areas have generally become smaller overall, the shapes of some contours may have changed or shifted over time, decreasing significant noise exposure in some areas, but also exposing new areas to significant noise. For example, while the DNL 65 dB area around Los Angeles International airport decreased from approximately 13 to 11 square miles in total area from 1987 to 2011, the shape of the contour changed and now includes different communities (see fig. 3). Improvements in aircraft technology, spurred by federal mandates and industry actions to reduce aircraft noise levels, have been the largest contributor to the shrinkage in airport-noise-exposed populations and noise contours. FAA and airport officials we spoke with generally agreed that the phase out of the loudest aircraft—specifically, stage 1 and stage 2 aircraft weighing over 75,000 pounds—by 2000 and improved aircraft and engine technology are the most significant factors causing noise contours to shrink. For example, reduced air velocity moving through improved engines has reduced engine noise. Likewise, acoustical liners and improved air flap designs have reduced airframe noise.factors that may have contributed to decreased airport noise exposure include the implementation of flight procedures that can, for example, direct air traffic over less populated areas during arrivals and departures. AIP noise grants have been widely used by airports and have provided noise mitigation to thousands of people. However, in recent years, the program has benefited fewer people and FAA has not met its program goals. In light of the shrinking airport noise contours discussed above, FAA’s enforcement of grant eligibility criteria—related to noise exposure maps and the assessment of interior residential noise—creates a risk that some noise grants may not have met eligibility criteria, especially in the edges of the noise contour where noise may be below DNL 65 dB. FAA has recently issued guidance to address these areas of grant eligibility criteria, which if followed should reduce the risk of making ineligible grants. In addition, FAA’s overall strategic goal for its noise-related activities is not linked to the results of noise grant investments.