Since the introduction of turbojet aircraft in the late 1950s for commercial passenger service, airport-related noise has generated controversy with many surrounding communities and emerged as a constraint on airport development. Airport-related noise emanates primarily from the takeoff and landing of aircraft, but engine maintenance and the taxiing of aircraft on runways are some of the other activities that also contribute to airport- related noise. New technology has been making aircraft quieter, and since 1969 the Federal Aviation Administration (FAA) has been limiting the noise that various aircraft are allowed to make. As a result, FAA estimates that the population exposed to very high noise levels will have declined from 7 million in 1975 to an estimated 600,000 in 2000. But in spite of the recent transition to quieter aircraft, expected growth in air traffic may result in little or no net reduction in overall noise levels generated by individual airports. Furthermore, concerns about airport-related noise may impede the development of any needed additional capacity in the national network of airports. The Congress has recognized the importance of developing a safe and efficient national airport system that meets the nation’s present and future aviation needs. As a result, federally authorized investment in a national airport system, including noise reduction projects, has totaled about $3 billion a year in recent years. FAA has primary responsibility for implementing federal programs addressing noise issues associated with civilian airports. In order to facilitate the development of a safe and efficient national airport system, FAA undertakes several activities that help airports and communities reduce airport-related noise or mitigate its effects. FAA must consult with the Environmental Protection Agency regarding some of its responsibilities. FAA’s activities focus on three areas: (1) reducing aircraft- generated noise at its source—the aircraft; (2) changing an airport’s use of its runways and/or implementing different flight operations; and (3) mitigating the effects of existing noise levels on surrounding communities. Airport-related noise can be lowered by reducing the noise that aircraft emit when they take off from and land at airports. New technology allows aircraft manufacturers to design and construct quieter aircraft. For aircraft already in service, noise levels can be reduced by (1) installing quieter engines, (2) installing equipment that reduces the noise of existing engines, and (3) modifying aircraft use and operations in ways that reduce aircraft- generated noise. FAA has actively engaged in efforts to reduce aircraft noise since the 1960s. The agency sets the noise standards aircraft must meet to be certified as airworthy and establishes the regulations that govern the operation of those aircraft at U.S. airports. The Federal Aviation Act of 1958, as amended in 1968, gave FAA the authority to regulate aircraft design and equipment in order to reduce noise. Pursuant to that act, FAA issued regulations in 1969 that established noise standards for new designs of civil subsonic turbojet aircraft. According to an aircraft design expert, the purpose of those noise standards was to ensure that the best available noise reduction technology was used in new aircraft designs. Initially, these regulations prescribed noise standards that applied only to new types or designs of turbojet aircraft (as well as certain propeller aircraft). In 1973, FAA amended its regulations to apply the noise standards to all newly manufactured aircraft, whether or not the aircraft design was new. In 1977, additional amendments established lower noise standards for all new aircraft, as well as the concept of noise “stages.” Aircraft meeting the original 1969 standards were categorized as “stage 2” aircraft; those meeting the more stringent 1977 standards were categorized as “stage 3” aircraft; and aircraft meeting neither standard were categorized as “stage 1” aircraft. In addition to establishing noise standards, FAA controls aircraft noise by regulating aircraft operations. In 1976, FAA amended its regulations to prohibit all certificated stage 1 subsonic turbojet aircraft weighing more than 75,000 pounds from flying into or out of U.S. airports after January 1, 1985, unless their engines had been modified or replaced to enable them to meet the stage 2 or stage 3 noise standards. However, the Aviation Safety and Noise Abatement Act of 1979 directed FAA to grant exemptions from compliance until January 1, 1988, to turbojet aircraft with two engines and fewer than 100 passenger seats. In 1990, the Airport Noise and Capacity Act required civil subsonic turbojet aircraft weighing more than 75,000 pounds to comply with stage 3 noise standards by December 31, 1999, or be retired from service. To meet this requirement, the engines on stage 2 aircraft could be modified or replaced. In addition to regulating aircraft-generated noise, FAA supports aviation research related to noise. In particular, FAA is working with the National Aeronautics and Space Administration to develop new technology to reduce aircraft noise. By changing use and/or operations, airports can reduce airport-related noise or mitigate its effects. For example, an airport can restrict noisy aircraft maintenance activities to areas where noise barriers can muffle the sound. Aircraft arrival and departure flight paths, as well as runway use, can be changed to minimize flights over densely populated areas. Airports can also mitigate noise impacts by seeking FAA approval to restrict certain aircraft to takeoffs and landings during the day, when their impact on nearby communities is considered less than during the night. FAA is involved in many of these activities. For example, FAA must approve any restriction on an aircraft’s access to an airport or on allowable noise levels if the restriction involves stage 3 aircraft or is beyond those imposed by federal regulations. Thus, if an airport wants to restrict any stage 3 aircraft to daytime operations, it must obtain FAA’s approval. FAA must also approve and implement changes in flight paths. Furthermore, FAA administers airport development funding programs, which can finance the construction of runways and taxiways that enable aircraft to use different takeoff and landing routes to minimize flights traveling over densely populated areas. Mitigation activities can reduce the impact of airport-related noise on the communities surrounding an airport. For example, buildings in nearby communities can be soundproofed and building codes can be changed to require improved sound suppression construction; noise barriers can be constructed; and airports can acquire land to prevent uses that are incompatible with the prevailing noise exposure levels. Communities can also exercise their authority over land use planning to help prevent the future development of land for activities that are noise-sensitive—such as those occurring in residences, schools, churches, and hospitals—in areas exposed to high noise levels. FAA supports mitigation efforts through two programs that provide federally authorized funds for airport projects that mitigate the effects of noise, and one program that encourages airports to identify and address the noise impacts of their airports on nearby communities. The Airport Improvement Program (AIP) and the Passenger Facility Charge (PFC) program provide federally authorized funding that, among other purposes, can be used to help mitigate the effects of airport-related noise. The AIP, established by the Airport and Airway Improvement Act of 1982, provides federal grants—funded by congressional appropriations from the Airport and Airway Trust Fund—for developing airport infrastructure, including projects that reduce airport-related noise or mitigate its effects. Airports must provide a “matching share” for AIP-funded projects, ranging from 10 percent to 25 percent of a project’s total cost, depending on the type of project and the size of the airport. Two categories of AIP grants are available—apportionment and discretionary. Apportionment funds are distributed by a statutory formula to commercial service airports according to the number of passengers served and the volume of cargo moved, and to the states according to a percentage of the total amount of the appropriated funds. Discretionary funds—for the most part, those amounts remaining after apportionment funds are allotted and certain other amounts are “set aside” for special categories, including noise-related projects—can generally be awarded for eligible projects at any eligible airport, including general aviation airports, which do not receive apportionment funds. Only airports included in FAA’s National Plan of Integrated Airport Systems are eligible for AIP grants. The National Plan of Integrated Airport Systems identifies those U.S. airports that constitute the national airport system, which is designed to ensure that every part of the country has an effective aviation infrastructure. There are 529 commercial service airports—those that receive apportionment funds—and 2,815 general aviation airports (for a total of 3,344 airports) in the current national plan. Furthermore, all projects funded with AIP funds—whether apportionment or discretionary—must be approved by FAA. However, FAA will not approve any grant for any kind of project without written assurances that the airport will take appropriate action, to the extent possible, to restrict the use of land near the airport to uses compatible with airport operations. The AIP funds noise mitigation projects in two ways. First, a specified portion of AIP appropriations is “set aside” by statute specifically for projects that address airport-related noise levels and their effects. Only projects relating to noise may be funded from this set-aside. Table 1 identifies the portions of AIP funds that have historically been set aside for noise. In addition to being eligible for these set-aside funds, projects addressing airport-related noise may compete with other airport development projects for other AIP grants. The second program providing federally authorized funds for mitigating airport-related noise—the PFC program—is a voluntary program that enables airports to impose fees on boarding passengers—known as passenger facility charges—and retain the money for airport infrastructure projects, including noise reduction. Under this program, authorized by the Aviation Safety and Capacity Expansion Act of 1990, commercial service airports may charge boarding passengers a $1, $2, or $3 fee. Airports are not required to impose the fee, but airports wishing to participate in the program must seek FAA’s approval both to levy the fee and to use the revenues for particular development projects.