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Volume 14,Issue 3 Autumn 2012

Careful Studies Demonstrate Effectiveness of Voluntary Noise Abatement Efforts and Permanent Monitoring Systems in Reducing Noise Exposure

This article summarizes two carefully conducted technical studies that demonstrated conclusively that voluntary noise abatement takeoff procedures can achieve measurable noise reduction, that citizens can readily notice the improvement, and that aircraft monitoring systems are a particularly valuable tool for use in designing and optimizing procedures, educating pilots in their proper application, and illustrating the benefits to citizens. Airports and aircraft operators use a broad range of noise abatement techniques to minimize noise impacts. One major category is “noise abatement departure profile” (“NADP”) procedures. NADP procedures involve specific steps in applying and changing power, flap, acceleration, speed, climb rate, climb angle, and other settings from start of takeoff roll until the aircraft is at cruise altitude to reduce noise over sensitive land uses. Overall, departure procedures fall into three basic categories: (1) “close-in” NADPs for use on runways where there are sensitive land uses relatively near the takeoff end of the runway; (2) “distant” NADPs for use on runways where there is an extended area of non-sensitive land uses off the takeoff end of the runway; and (3) “standard” procedures for use on where sensitive land uses are relatively evenly distributed. In practice, the two NADP procedures can be customized for a broad range of specific conditions, resulting in a spectrum of procedures across the two categories. For example, a recent international survey identified 20 different NADP procedures employed by a sample of 19 airlines.[ International Civil Aviation Organization, Doc 9888, Noise Abatement Procedures: Review of Research, Development and Implementation Projects – Discussion of Survey Results, Montreal, Quebec, Canada, 2010.] The International Civil Aviation Organization (ICAO) provides guidance on design and implementation of NADPs.[ International Civil Aviation Organization, Doc 8168, Procedures for Air Navigation Services – Aircraft Operations (PANS-OPS), Part V, Chapter 3, Montreal, Quebec, Canada, 2010.] The ICAO guidance calls the close-in procedure “NADP1” and the distant procedure “NADP2.” As an illustrative example, the following figure presents graphical descriptions of the two ICAO procedures for a 737 aircraft.[ Source:, last referenced September 9, 2011.] Residents living under takeoff flight paths often are surprised to learn that pilots apply such procedures on a voluntary basis, and that airport operators and air traffic controllers cannot formally require pilots to follow them. However, with careful communication and education, citizens quickly and easily understand that mandatory application would be inconsistent with the primary consideration of safe aircraft operation. With this limitation understood, citizens often ask whether the voluntary implementation is effective. Two U.S. airports recently evaluated NADP procedures with extensive pilot, airport, aircraft operator, and citizen involvement, and detailed noise measurement analyses. The studies demonstrated that voluntary NADP procedures result in measurable and readily detectible noise reduction. The studies were at: Van Nuys Airport (VNY) in Van Nuys, California, which is owned and operated by the Los Angeles World Airports (LAWA), and Witham Field (SUA) in Stuart, Florida, which is owned and operated by Martin County, Florida. The following paragraphs summarize highlights from these initiatives. Van Nuys Airport NADP Investigation In early 2011, LAWA completed a multi-year noise abatement study at VNY that considered options for improving its noise abatement program. The study demonstrated that LAWA and airport users are collaborating to achieve noise abatement goals in a highly successful manner, and that voluntary measures have led to significant and measurable improvement. The analysis of one voluntary measure – the “Fly-Friendly Target Noise Level Program” – clearly illustrates the effectiveness of voluntary NADP efforts and the value of a permanent noise monitoring system in achieving noise-reduction benefits. Working with the VNY Citizens Advisory Council (CAC), LAWA established the Fly-Friendly program in 1994. In simple terms, the program sets aircraft-type-specific noise-level targets for jet departures on VNY’s primary departure runway. LAWA measures actual departure noise levels and sends letters to each aircraft operator that exceeds the applicable target. LAWA offers assistance to operators to establish procedures to reduce noise levels below the targets and has found that operators appreciate and take advantage of the offer. The analysis utilized measurement data from the VNY monitoring system for January 1998 through May 2007, including measurements for over 120,000 departures in over 50 jet aircraft types. LAWA measurements reveal that this purely voluntary measure has been highly successful in reducing noise levels; the percentage of jet departures exceeding targets has been cut in half – from over 11% to approximately 5.5%. The average measured jet departure noise level has been reduced by over two decibels, which translates into a significant reduction in overall noise levels under industry-accepted standards. The figure on the right is a selected example of analysis results for a single aircraft type – the Lear 35 corporate jet. It illustrates one of the study’s most significant findings, that measured departure levels are noticeably lower for more frequent operators. This result is attributed to the fact that more frequent operators have greater familiarity with program objectives, and more opportunities to optimize their takeoff procedures. The airport’s permanent noise monitoring system is a critical tool in the familiarization and optimization efforts, since it provides highly accurate, objective data that operators can use in assessing and refining procedures. The study also led LAWA to propose enhancements to extend the effectiveness of the Fly-Friendly program, including identification of updated targets for the full fleet of jet models currently operating at VNY and establishment of an annual awards program to recognize the efforts of the best-performing operators. LAWA is working with the CAC and the Van Nuys Airport Association (which represents VNY business interests) to flesh out program implementation and notification mechanisms. Further details on the Fly-Friendly program are available under the “Airport Information / Noise Management” section of LAWA’s VNY website, at Witham Field NADP Investigation While LAWA was able to develop, assess, and update its NADP program based on extensive data from an established permanent monitoring system, Martin County, Florida, developed its NADP program for Witham Field as one of the first steps in the design of its system. The Witham Field study involved a high degree of community, airport, pilot, and aircraft operator participation, starting with a highly participatory process to identify optimum procedures to test. That first step led to the selection of two particularly promising options, based on noise modeling and informal citizen and pilot impressions of procedures flown by different operators. The second study phase involved conducting controlled flight demonstrations of the two selected procedures in two aircraft types, with consulting engineers conducting measurements at two locations in the community, as shown below. Citizen, aircraft operator, and airport observers were stationed at the two locations, to provide a “human” assessment in addition to the formal decibel readings. Citizen representatives also observed flight procedures in the aircraft cockpit and assisted in logging aircraft altitudes and speeds for use in detailed noise modeling to supplement the measurements. Each procedure was flown twice in each aircraft type. The measurements and observations led to surprisingly consistent conclusions, from multiple perspectives: First, the measurements revealed that one procedure was clearly quieter than the other in terms of measured noise levels and the time noise levels were above the locally accepted noise threshold. Second, the same procedure was preferable for both aircraft types. Third, observers noticed a clearly detectable difference between the two procedures; one was clearly quieter. Fourth, the observers’ impressions were entirely consistent with the measurements. Fifth, the same procedure was preferable at both of the measurement / observation locations. Measurements revealed a 6 to 8 decibel reduction in the total noise exposure during the aircraft flyovers. From a cumulative exposure perspective, this noise reduction is equivalent to reducing operations in the aircraft using the preferred procedure by a factor of five, assuming they otherwise would have used the alternate procedure. The study results led to unanimous selection of a preferred procedure by all participants, with subsequent endorsement by the airport’s noise abatement committee, the Board of County Commissioners that governs airport operations, and by the U.S. Federal Aviation Administration. The study results also provided critical information that the County used in designing and obtaining a permanent noise monitoring system for use in implementing its noise abatement program, training pilots, and presenting results to the public. Martin County won multiple statewide industry awards for this highly successful cooperative effort.
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