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Noise Management and Public Response 105 alternative operating configurations. Furthermore, except for the most sophisticated systems, measurements do not reflect the complete annual condition usually required by planning doc- uments. Modeled noise levels can capture hypothetical cases and alternative conditions that are impractical to measure over any length of time. Computer models can also interpolate the noise patterns across any area, based upon the input provided to the model. Consequently, great care must be taken to the preparation and verification of input data, including flight track locations, types and numbers of aircraft, their distribution through the day, their use of various runways, and the rates at which they climb or descend from the airport. Once these variables are coded and processed, the projected noise levels of individual aircraft may be compared to measured noise levels of similar aircraft flying comparable flight paths to verify the validity of the modeling effort. If not comparable, the input data may be adjusted to provide a better fit with the measured data for individual aircraft. Measured Noise Measurements of single aircraft events, collected with a properly calibrated scientific noise mea- surement instrument in the field, are nearly always more accurate than the computer-modeled noise level--for that same operation, and if the portion of the measured noise attributable to non- aircraft sources is filtered out. Further, Section 14.4f of FAA Order 1050.1E, Change 1, Appendix A, provides that noise measurements are not required in federally funded environmental documents, nor should they be used to calibrate the computer model. To be fully acceptable for inclusion in federally sponsored environmental evaluations, measure- ments should be conducted in accordance with the programmatic guidelines presented in 14 CFR Part 150 guidelines (FAA Advisory Circular 150/5020-1, Noise Control and Compatibility Planning for Airports, FAA, 1983). Notably, measured data is required by state law to be reported in some locations. For example, in California, measurements are required to be reported quarterly to the State Division of Aeronautics under the California Airport Noise Standards (149) Under Section 5032 of the Code; the mea- sured data recorded by sets of permanent noise monitors serves as the basis for noise contour mapping at each airport designated as a "noise problem airport". Currently, nine large California air carrier airports and Van Nuys Airport are designated to be "noise problem airports". Aircraft Noise-Based Vibration and Rattle Persons who reside near airports will occasionally comment about vibration or rattle, which they associate with aircraft noise events. When related to aircraft, these phenomena are normally caused by low frequency noise generated during takeoff roll or the application of reverse thrust that is often limited in area to locations near the airport. A recent assessment of the available literature regarding this relationship (150) indicated that there is no generally accepted relationship between low frequency and annoyance. Neither have any studies indicated a causal relationship between low-frequency noise generated by aircraft and structural damage to any buildings off of an airport, although the rattle generated by the low-frequency vibrations may be considered annoying by some persons. Low-frequency noise and rattle was the subject of a recent PARTNER project, the results of which may be found at http://web.mit.edu/aeroastro/partner/projects/index.html. (151) 6-8 Sound Insulation Programs for Noise Abatement Since early recorded history, the Egyptians and Romans have used cork as a renewable source of thermal insulation for pipes and roofs. What they didn't realize was that they were also the first

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106 Aircraft Noise: A Toolkit for Managing Community Expectations humans actually providing sound insulation to their homes. Even back in 1937, The Washington Post published an article stating how insulating materials were being used for thermal and sound insulation. However, it really wasn't until the 1960s when large jet aircraft became common at commer- cial airports that aircraft noise began to be recognized as a real issue in residential areas around airports. LAX started one of the first airport-sponsored sound insulation programs in 1967. However it really was not until The Aviation Safety and Noise Abatement Act (ASNA) of 1979 that sound insulation programs really started to take off. ASNA permitted the FAA to provide funding noise mitigation projects at airports. One of the first projects in the early 1980s was the treatment of homes near Boston's Logan International Airport (BOS). FAA funds are provided once an airport has an approved Noise Compatibility Program (NCP), but the FAA will also provide funds for buildings used for educational or medical pur- poses without an approved NCP. A sound insulation program is comprised of several phases including the following: Startup activities; Design and implementation phase; Bid and award phase; Construction phase; and Program evaluation. The startup activities include the review of existing program documents, development of a pol- icy and procedures manual, determining the community outreach requirements, reviewing acoustical treatment options, and coordinating with the local jurisdictional agencies and the FAA. The design and implementation phase includes undertaking homeowner outreach, schedul- ing and conducting initial assessment visits, performing pre-construction acoustical testing, eval- uating the mechanical and electrical systems, performing a structural and hazardous materials evaluation, and preparing final bid documents. During the bid and award phase, a pre-bid con- ference is held, along with a pre-bid walk through, followed by a review of bids, and the contract award. In the construction phase a pre-construction conference and walk through is held followed by pre-construction review. Construction begins and work includes construction administra- tion and inspections, followed by contract closeout. The final program evaluation would include post-construction acoustical testing, undertaking homeowner satisfaction surveys, preparation of a final program report, and preparation of the documentation to close-out the FAA Grant. One of the biggest issues facing airports today, with regards to their sound insulation program, is changing DNL/CNEL contours. Many airports have large ongoing programs with the limits defined as part of an approved NCP, some going back to the 1990s. Since that time the airline industry has changed dramatically. Overcapacity and the 9/11 attacks, among other reasons, have caused carriers to cutback and phase out the noisier hush-kitted aircraft. Quieter regional jets became more common and many carriers either went bankrupt or restructured and down- sized due to financial considerations. More recently the high cost of fuel has resulted in sched- ule reductions, further airline bankruptcies, and mergers. The result is that many contours around airports have shrunk dramatically. They are much smaller than the contours upon which the sound insulation program was based in the original NCP. In many cases the FAA is requiring airports to update the noise contours, resulting in smaller sound insulation programs. Where residents were initially in the program, they now fall outside the program limits and the airports have to deal with the public relations fallout as a result of these diminished contours.