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104 Aircraft Noise: A Toolkit for Managing Community Expectations Local government may establish criteria for the regulation of aircraft noise when the aircraft is parked on an apron or ramp, or is under maintenance in an active run-up configuration. This finding was confirmed by the U.S. District Court in its finding in National Aviation et al. vs. City of Hayward (1976) which decided that local noise control restrictions may be implemented by a community as an airport owner or operator, but not through its police powers. (148) The United States Congress passed the Airport Noise and Capacity Act (49 USC 47521) in 1990, which among other things included a National Aviation Noise Policy prohibiting locally based restrictions on Stage 3 aircraft without federal approval, while requiring phase out of Stage 2 air- craft weighing more than 75,000 pounds by 2000. It also authorized Passenger Facility Charge (PFC) funding for airport development. Although the FAA has published guidance to the compatibility of various land uses with dif- fering levels of aircraft noise (as described by DNL) through its 14 CFR Part 150 guidance, the agency does not have the authority to manage or control land uses on property beyond the boundaries of federal ownership off the airport. Further, the airport sponsor is responsible for the usage of land within the boundaries of the airport, but must comply with federal guidelines to assure the safe operation of any aircraft using the airport (i.e., to avoid the introduction of obstructions on the airport). Local communities or states may regulate the use of land in areas off the airport, including zoning and subdivision, review of development propositions, and the regu- lation of the heights of structures. Frequently the federal and local agencies work together to develop plans for the compatible development of lands surrounding the aviation facility within the framework of community- wide planning needs and airport need. Measured versus Computer-Modeled Noise Levels The airport manager will frequently be asked to explain the difference between noise levels that have been measured in the field and noise levels for the same location that have been mod- eled by computer software. Frequently there will be differences of several decibels between two numbers for the same place. Modeled Noise At most airports, noise levels are described by either a series of contour lines representing points of equal noise exposure or by projected single event or cumulative noise levels at selected locations. Because it would require extensive sets of noise measurement equipment placed over a wide area for long periods of time to develop contours from measured data at costs well beyond the means of all but the most affluent airports computer models have been developed to simulate the noise patterns created by aircraft. Two models are accepted by the FAA's Office of Environment and Energy (AEE) for use on federally funded airport noise studies these are the Integrated Noise Model (INM) and the Helicopter Noise Model (HNM). Under the provisions of FAA Order 1050.1E, Change 1, Appendix A, Section 14.4d, noise contours required for various environmen- tal analyses conducted with federal funding assistance must be developed using the INM or HMH. In studies of flight track relocations above 3,000 feet above the ground level, the Noise In Route System (NIRS) model is also acceptable, but generally applied only to work sponsored by the Air Traffic Organization. Other models may be used if prior approval is sought from and certified by the AEE as having results equivalent to those produced by the INM or HNM. For planning evaluations and assessments of environmental effect conducted under federal grant or for federally funded development, the modeling of noise levels is considered more acceptable than the use of measurements for several reasons. Measurements cannot reflect con- ditions that do not exist, i.e., they cannot provide projected noise levels for future years or for