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For Greener Skies: Reducing Environmental Impacts of Aviation 2 Noise Despite extensive growth in air transportation over the last several decades, advanced technologies and more stringent regulatory standards have greatly reduced the number of people adversely affected by noise. Unfortunately, this trend is unlikely to continue, and public opposition to airport noise is becoming more—not less—of an impediment to the growth of the air transportation system. Even though fewer people are exposed to high levels of aviation noise, local communities still experiencing levels that residents perceive as unacceptable are increasingly willing to oppose expansions of airport facilities and operations. Although NASA’s noise reduction goals are appropriate and additional technological advances are possible, the level of funding for federal research programs is too low to achieve the goals on schedule (see Table 1-4) or to remove noise as an impediment to the growth of aviation. The vast majority of federal expenditures on aviation noise are allocated to noise abatement at individual airports rather than to research on quieter engines and aircraft, which would ultimately reduce aviation noise nationally and internationally. More effective interagency coordination and a more balanced allocation of funds would support a vigorous and comprehensive research program that could mature a wider array of promising technologies and reduce the time it takes for new technology to become prevalent in the commercial fleet. TRENDS IN AVIATION NOISE As indicated in Chapter 1 and Figure 1-1, noise is the single greatest environmental concern facing air carriers and airports today. Officials at 29 of the 50 busiest U.S. airports asserted that noise from airport operations was their most serious environmental concern, and officials from 22 of the airports stated that noise will remain the top concern in the future because of expected increases in operations and in the number and stringency of noise restrictions (GAO, 2000). Noise concerns limit aviation capacity by delaying runway expansion (see the example in Box 2-1) and causing flight cancellations and delays on a daily basis (see Box 2-2 for three typical examples from a single airline during a week in January 2000). The net result is higher airline operating costs and higher ticket prices. Further, noise is often a principal focus for community groups and larger nongovernmental organizations that act to oppose runway expansion. Part 36 of the Federal Aviation Regulations, which defines aircraft certification requirements related to noise, was issued in 1969, and federal legislation aimed at reducing the annoyance associated with aviation noise sources was first enacted in 1972 (Noise Control Act, P.L. 92-475). Since that time, a variety of technological and operational advances have led to a reduction in the average perceived noise from a single aircraft operation of greater than 10 EPN dB (effective perceived noise level in decibels—a measure of aircraft noise that is closely linked to levels of human annoyance).1 Note that a reduction of 10 EPN dB corresponds to roughly 50 percent less annoyance for a single event. Figure 2-1 shows centerline takeoff noise levels measured during FAA certification tests for individual aircraft as a function of the date at which the aircraft model was certified. (During certification, an aircraft must also meet certification standards for sideline takeoff noise and approach noise.) The large reduction in noise in the late 1960s and early 1970s was a result of the introduction of the turbofan engine. While the primary motivation for the use of turbofan engines was reduced fuel consumption, less noise was an important ancillary benefit. In the 1980s and 1990s, changes were more evolutionary, with increased by-pass ratio engines, better 1 For detailed information on how effective perceived noise level is measured, see Appendix B of Federal Aviation Regulations Part 36—Noise Standards: Aircraft Type and Airworthiness Certification, which is codified in 14 CFR 36 and available online at <http://www.access.gpo.gov/nara/cfr/cfrhtml_00/Title_14/14cfr36_00.html>.
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For Greener Skies: Reducing Environmental Impacts of Aviation BOX 2-1 Example of Delays in Runway Expansion Due in Part to Aviation Noise In the early 1970s, MASSPort, the public authority that manages Logan International Airport in Boston, attempted to add a runway, runway 33R/15L, to parallel existing jet runway 33L/15R. Construction started, but members of the community blocked the bulldozers and stopped the work. As a result, MASSPort was enjoined by the court from constructing any more runways. The injunction is still in effect today. As a result of the incomplete construction effort, runway 33R/15L exists, but it is only 2,557 feet long—too short by far to handle large jet aircraft. From 1975 to 2000, Logan’s total operations increased from about 300,000 to 500,000 takeoffs and landings per year. Within the past 2 years, MASSPort proposed a new, 5,000-foot runway, runway 14/32, to be located at the southern edge of the airport. This runway would service smaller aircraft (commuter and light aircraft), which currently constitute 40 to 50 percent of Logan’s operations. It would also be unidirectional in that the only operations permitted would be landings on 32 and departures on 14. The local community has also opposed construction of this runway. SOURCE: Personal communication, Nancy Timmerman, Manager, Noise Monitoring Systems, Massachusetts Port Authority, February 2001. BOX 2-2 Examples of Flight Delays and Cancellations Directly Caused by Aircraft NoiseRestrictions January 5, 2001. Delta Air Lines Flight 1285 left John F. Kennedy International Airport in New York City with 98 passengers bound for Ronald Reagan Washington National Airport, in Washington, D.C., and 31 passengers bound for Atlanta. Flight 1285 was late departing New York because weather conditions required de-icing prior to takeoff. As a result, the flight was unable to reach Washington, D.C., until after the noise curfew at National Airport. Therefore, Flight 1285 was diverted to Washington Dulles International Airport, where an additional 32 passengers boarded the plane to go to Atlanta. Meanwhile, 33 passengers at National Airport who had been booked for the leg to Atlanta had to make other arrangements. January 7, 2001. Delta Flight 198 was scheduled for a night flight from San Diego to Cincinnati with 38 passengers. The flight crew was on another flight that was late arriving in San Diego. As a result, Flight 198 had to be canceled because it was unable to take off prior to the noise curfew at San Diego International Airport. January 11, 2001. Delta Flight 1670 was scheduled to fly from San Diego to Dallas/Fort Worth. The aircraft needed for this flight should have arrived in San Diego the previous evening as Flight 2115 from Salt Lake City. That flight, however, and its 58 passengers had been diverted to Los Angeles, apparently because of the noise curfew (coupled with “field conditions”) at San Diego International Airport. Delta Air Lines used a bus to get the passengers on Flight 2115 to San Diego after they deplaned at Los Angeles, and Flight 1670 was canceled on the following morning because no aircraft were available in San Diego. acoustic liner technology, and other engineering changes being gradually introduced. The development of many of these improvements was supported by NASA research programs. Between 1970 and 2000, average aircraft capacity increased from 113 seats to 158 seats, and the average number of engines per aircraft dropped from 3.2 to 2.3 (averages are weighted by distance traveled by different aircraft). Larger aircraft with fewer engines require engines with more thrust, which produce more noise, and this has offset some of the technological gains. The differences between the noise levels of the various aircraft shown in Figure 2-1 arise from differences in technology level, overall size and weight, and number of engines. Variations due to size and/or weight and number of engines are accounted for in the certification regulations: heavier aircraft with more engines are generally allowed higher noise levels. Figure 2-1 indicates that the pace of technological change has been roughly constant—an improvement of about 3 dB per decade—over the past 40 years. ICAO’s Committee on Aviation Environmental Protection has recently recom-
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For Greener Skies: Reducing Environmental Impacts of Aviation FIGURE 2-1 Trends in aircraft noise levels: effective perceived noise level during take off for aircraft at maximum takeoff weight as a function of certification date. SOURCE: Lukachko and Waitz, 2001.
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For Greener Skies: Reducing Environmental Impacts of Aviation TABLE 2-1 Effects of Noise on People DNL (dB) Qualitative Description of Community Potential for Hearing Loss Percent of Population Highly Annoyed Average Community Reaction General Attitude 75 and above Hearing loss may begin to occur >37 Very severe Noise is likely to be the most important of all adverse aspects of the community environment 70 Hearing loss not likely 22 Severe Noise is one of the most important adverse aspects of the community environment 65 Hearing loss will not occur 12 Significant Noise is one of the most important adverse aspects of the community environment 60 Hearing loss will not occur 7 Moderate to slight Noise may be considered an adverse aspect of the community environment 55 and below Hearing loss will not occur 3 Moderate to slight Noise considered no more important than various other environmental factors SOURCE: FICON, 1992. mended reducing the noise certification standard by 10 dB (cumulative), which is equivalent to reducing the noise at each of the three certification points (takeoff, sideline, and approach) by approximately 3 dB. In part, this reduction was recommended because it represents the current state of feasible technology. Figure 2-1 shows the change in effective perceived noise for a single aircraft operation during certification tests. However, for assessing the noise impact of a specific airport on the local community, it is more useful to consider an appropriate average of the noise produced by the flight operations from that airport over a 24-hour period. One such measure is the day-night average sound level (DNL), a metric for assessing annoyance from aircraft noise that has been adopted by the FAA for aircraft noise compatibility planning. It is assumed in forming this measure that operations occurring at night are more annoying than those occurring during the day because of the potential for sleep disturbance and because background noise is lower at night. Therefore, DNL is weighted to count each takeoff or landing between 10 P.M. and 7 A.M. the same as 10 daytime takeoffs or landings of equal loudness. A summary of personal responses to noise and their relation to DNL level is shown in Table 2-1. At 55 dB DNL (indoors or outdoors), noise is considered no more important than various other environmental factors, and only about 3 percent of the population affected will be highly annoyed by noise. At 60 dB DNL, research suggests that the annoyance rate will be approximately 7 percent, and noise may be considered an adverse aspect of the community environment. At 65 dB DNL, 12 percent of the population will be highly annoyed and noise is one of the important adverse aspects of the community environment. (It should be noted that the median outdoor exposure to noise in urban areas is 59 dB DNL, with a range of 58 to 72 dB.) Corresponding ranges for suburban and wilderness areas are 48 to 57 dB and 20 to 30 dB, respectively. Although areas with levels greater than 65 dB DNL are given priority for federal noise abatement funds, most complaints regarding aviation noise come from areas with a DNL less than 65 dB, because the number of people living in areas with a DNL of 55 to 65 dB may be 5 to 30 times the number of people living in areas with greater than 65 dB DNL; airports themselves occupy much of the land where the DNL is higher than 65 dB, whereas the land with DNLs between 55 and 65 dB is typically used for other commercial and residential purposes. Figure 2-2 shows the areas around San Francisco International Airport where the DNL exceeds 55 and 65 dB. The complexity of the issues surrounding public response to aviation noise is further articulated in Box 2-3.2 Success in preventing deviations from the “normal noise experience” can be a factor in reducing annoyance from aircraft noise. Atlanta’s Hartsfield International Airport, the world’s busiest, receives relatively few noise complaints from citizens who live under departure and approach paths, in part because flight crews and FAA controllers consistently keep aircraft following the specified flight tracks, thereby minimizing variation in noise levels that local residents have come to expect. The number and duration of jet noise events can also affect levels of annoyance. Studies have shown that, on average, a 3-dB increase in noise level does not increase the level of annoyance if the noise lasts for half as long or half the number of noise events occurs. 2 For additional information on DNL and the development of noise exposure maps, see section 150.7 and Appendix A of Federal Aviation Regulations Part 150—Airport Noise Compatibility Planning, which is codified in 14 CFR 150 and available online at <www.access.gpo.gov/nara/cfr/cfrhtml_00/Title_14/14cfr150_00.html>.
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For Greener Skies: Reducing Environmental Impacts of Aviation FIGURE 2-2 Extent of high-noise areas around San Francisco International Airport, 1998-1999. SOURCE: Fleming, 2001. BOX 2-3 Aviation Noise Challenges The FAA has estimated that domestic air travel will increase 3.6 percent annually between 2000 and 2011, for cumulative growth of almost 48 percent during that time period. To build the infrastructure necessary to accommodate that growth and to handle the additional aircraft it will bring, both the airline industry and local officials must address the concerns of citizens who live near, and in some instances considerable distances from, airports. When air traffic patterns change, complaints may be received from citizens who live under the new flight paths, even if the noise is at relatively low levels. For example, in 1987 the FAA restructured the air routes in the northeastern United States, including the metropolitan New York City area. The purpose of the restructuring was to make more efficient use of the airspace and to enable continued growth at the region’s airports. As a result of this airspace redesign, airplanes started flying over areas of New Jersey that had not previously had overflights. The noise heard on the ground from these flights was low compared with the standards for annoyance. However, a significant number of residents expressed (and 15 years later continue to express) great dissatisfaction with this situation. The reason given for their dissatisfaction is aircraft noise that they had not previously experienced. As another example, many of the noise complaints that the new Denver International Airport receives are from residents 40 miles away, in the vicinity of Boulder. Prior to construction of the new airport, its location was not considered to present a noise annoyance problem because the closest residential areas were nearly 10 miles away. Parts of the Boulder area, however, are isolated from both industrial and highway noise, and the relatively quiet environment makes a jet at 10,000 feet seem noisy when it passes overhead at climb thrust, particularly because residents had not experienced jet traffic overhead before the opening of the new airport.
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For Greener Skies: Reducing Environmental Impacts of Aviation FIGURE 2-3 Estimated trends in number of people affected by aircraft noise in the United States (number of people within 65 dB and 55 dB DNL as a function of time). SOURCE: Lukachko and Waitz, 2001. Infrequent, unexpected noise can also be more annoying than louder, repetitive jet noise. One municipality near the Atlanta airport has issued legal citations to an airline for nighttime ground testing of engines at high power. The proximity of the testing to residential areas, coupled with the time of night and the abruptness and intensity of the associated noise, contributed to a high level of annoyance. Now, when nighttime testing is required, the airline conducts the tests at a more distant location on the airport property. As shown in Figure 2-3, the number of people affected by aircraft noise has significantly decreased over the past 25 years. The large reductions in affected population shown in this figure have resulted primarily from three factors: improved technology (see Figure 2-1) low-noise aircraft operations enabled by advanced aircraft control, navigation, and surveillance technology and advanced air traffic management technology mandatory phaseout of old, relatively noisy (Stage 1 and 2) aircraft (see Figure 2-3) The impact of phasing out noisy aircraft is underscored by Figure 2-3. While the total number of Stage 2 aircraft corresponded to 55 percent of the fleet in 1990, these aircraft contributed to more than 90 percent of the total DNL levels at airports. Notably, the reductions in affected population shown in Figure 2-3 were achieved while the commercial aviation industry provided service to a steadily increasing number of people. An appropriate measure of the mobility provided by the aviation industry is revenue-passenger-kilometers: the number of people moved multiplied by the distance carried. As shown in Figure 2-4, mobility has increased sixfold over the past 30 years and is expected to continue to increase over the next 20 years at a rate of 3 to 5 percent per year. Estimates by the FAA suggest that further reductions in the number of people in the United States affected by noise will be small over the next 20 years because the current fleet is relatively new and no additional large-scale, mandatory phaseouts of older aircraft are planned. The approximately constant number of people affected results from a balance between projected improvements in technology and projected increases in flight operations. A simplified representation of the ratio of social costs to social benefits can be estimated by comparing the data on the number of people affected by noise and the amount of travel services provided, as shown in Figures 2-3 and 2-4, respectively. The number of people affected by noise has
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For Greener Skies: Reducing Environmental Impacts of Aviation FIGURE 2-4 Historical growth in mobility provided by U.S. commercial aviation. SOURCE: Lukachko and Waitz, 2001. been reduced by a factor of roughly 15, whereas the amount of travel services provided has increased by a factor of 6. Therefore, the number of affected people per unit of mobility provided has decreased by a factor of nearly 100 over the past 30 years. The foundation of this dramatic reduction has been technological advancements created by both the federal government and private industry. Airports and airlines still view noise as their most urgent environmental issue, however, because of greater public sensitivity to noise and other environmental problems. Increased local awareness of aviation noise causes more airports to impose noise restrictions (see Figure 2-5) and fosters the establishment of more nongovernmental organizations devoted to reducing aviation noise (see Table 2-2). Most of the federal research and development dollars spent on aviation noise are administered by NASA, with smaller fractions expended by the FAA and the Department of Defense (DoD). Among these organizations, it is primarily NASA’s role to carry out research and development. The FAA focuses on assessing noise compatibility, aircraft certification, and regulatory issues, although some development of aircraft noise modeling and assessment tools occurs within the FAA. DoD focuses more directly on issues of noise compatibility around and on military air bases. Typically, NASA’s work is intended to conduct basic research and early technology development to enable implementation of new technologies in products by industry. NASA often describes the maturity of technology using its own technology readiness scale. Much of NASA’s previous research in aircraft noise was designed to mature technology to a technology readiness level (TRL) of 6, but because of limited funding future research programs (as discussed below) will typically stop at TRL 4 (see Figure 2-6). Depending on a variety of business, regulatory, and technological factors, new technology at TRL 6 can take as long as 15 years to be implemented in commercial aircraft. Technology at TRL 4 takes even longer to be of practical value. Figure 2-7 shows the federal investments to reduce commercial aviation noise over the past 10 years (in constant year 2000 dollars). The net sum of these expenditures during that time is $440 million. Since the mid-1990s, the overall trend is downward. Under current plans, the level will stabilize at about $20 million per year, less than half of the average annual expenditure for the past 10 years. While definitive financial data are not available on industry expenditures for noise research and related application of this technology, one estimate places the total noise research work by the three major aircraft engine companies (General Electric, Pratt &
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For Greener Skies: Reducing Environmental Impacts of Aviation FIGURE 2-5 Trends in aircraft noise regulation: number of airports worldwide imposing various constraints and charges as a function of time. SOURCE: Boeing, 2001. Whitney, and Rolls-Royce) at between $10 million and $15 million annually. These companies spend additional resources, perhaps on the order of $30 million to $60 million over 2 years, to incorporate noise reduction technology in new engines during product development. Major aircraft companies are estimated to spend a comparable amount of money on noise reduction technologies both for research and development. It is difficult to make a quantitative statement as to how much of the technological change apparent in Figure 2-1 can be attributed to government expenditures. However, all industry representatives contacted by the committee found NASA research to be critical in advancing aviation noise technology, especially because NASA invests in higher-risk, longer-term research than industry. FAA noise abatement programs reduce exposure to noise, primarily by soundproofing buildings located near airports and by purchasing land to extend airport property (allowing residents and businesses to relocate elsewhere). Federal noise abatement activities are funded by the Airport Improvement Program and Passenger Facility Charge Program, using money collected from fees and taxes on passenger airline tickets. Money spent on abatement addresses the noise problem one airport at a time, and it can be very costly, with total expenditures for a single airport (from all sources— federal, state, and local governments and the airport authority itself) often amounting to several hundred million dollars. Advances in technology, however, reduce the burden nationally (and globally). Through 2001, $408 million had been spent on sound insulation for residential and school buildings around Chicago’s O’Hare International Airport. This is almost as much as the federal government’s entire noise technology research and development budget for the past 10 years. Although federal expenditures on noise research and development have been declining, federal expenditures on noise abatement have been increasing (see Figure 2-8). Perhaps more striking is the small amount spent on research and development compared with that for noise abatement. Over the past 10 years $3.2 billion has been spent on noise abatement—about 7 times more than federal expenditures on noise reduction research and development. The imbalance has been worsening in the past few years (see Figure 2-9). Furthermore, noise abatement cannot fully restore quality of life; soundproofing addresses only interior noise levels, and land purchases displace communities. The most effective— the only—long-term solution is to develop new technology that will lead to quieter aircraft. Finding 2-1. Growing Cost of Noise. The cost of aviation noise is significant and growing. Aviation noise reduces property values, contributes to delays in expanding airport facilities, and prompts operational restrictions on existing runways that increase congestion, leading to travel delays, high airline capital and operating costs, and high ticket prices. Finding 2-2. Technology Accomplishments and Goals. Over the past 30 years, the number of people in the United States affected by noise (i.e., the number of people who experience a day-night average sound level of 55 dB) has been reduced by a factor of 15, and the number of people affected by noise per revenue-passenger-kilometer has been reduced by a factor of 100. New technology has contributed significantly to these improvements. Recommendation 2-1. Balanced Allocation of Funds. Federal expenditures to reduce noise should be reallocated to shift some funds from local abatement, which provides near-term relief for affected communities, to research and tech-
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For Greener Skies: Reducing Environmental Impacts of Aviation TABLE 2-2 Nongovernmental Organizations Devoted to Reducing Aviation Noise State Name of Group Alabama Citizens Coalition for Airport Neighbor Rights (CCANR) Alaska Cruise Control, Inc. Peace and Quiet Coalition Arizona Mesa Community Alliance Quiet Skies Alliance Taxpayers for Responsible Planning California Alliance for a New Moffett Field Citizens Against Airport Pollution (CAAP) Citizens for Safe and Healthy Communities Citizens to Silence LAX El Toro Airport Info Site Move Against Relocating Choppers Here (MARCH) No More Noise Peninsula Aircraft Noise/Safety Information Committee People Over Planes Restore Our Airport Rights San Francisco Airport Roundtable San Lorenzo Citizens Against Airport Noise Uproar Colorado Alliance to Mitigate Aircraft Noise Boulder County Citizens Against Aviation Noise Colorado Citizens Against Noise Preserve Unique Magnolia Association District of Columbia Airport Coordinating Team Citizens for Abatement of Aircraft Noise (CAAN) Florida Citizens for Control of Airport Noise Stop the Boca Raton Airport Georgia PDK Watch Hawaii Citizens Against Noise of Hawaii Illinois Alliance of Residents Concerning O’Hare Indiana Save Our Skies Victims of Airport Expansion Kentucky Airport Neighbors Alliance Massachusetts Communities Against Runway Expansion (CARE) Community Transportation Alliance of Cape Cod Concerned Citizens Coalition Safeguarding the Historic Hanscom Area’s Irreplaceable Resources United Against MASSPort Minnesota Residents Opposed to Airport Racket (ROAR) South Metro Airport Action Council (SMAAC) Missouri Saint Charles Citizens Against Aircraft Noise Nevada Citizens for Airport Accountability New Jersey Alliance of Municipalities Concerning Air Traffic Branchburg/Readington Airport Coalition (BRAAC) New Jersey Coalition Against Aircraft Noise (NJCAAN) People Limiting Airport Noise and Expansion (PLANE) Quieter Environment Through Sound Thinking (QUEST) Runway 22 Coalition New York Citizens for Enforcement of MacArthur Airport Control Helicopter Noise Coalition of New York City Sane Aviation for Everyone (SAFE) Ulsterites Fight Overflights North Carolina Airport Noise Piedmont Quality of Life Coalition Raleigh Durham Airport Noise Committee Ohio Airport Neighbors Decide Akron/Canton Airport Noise Citizens Against Reckless Expansion Olmsted Falls Airport Committee Pennsylvania Bucks Residents for Responsible Airport Management Citizens Alliance for Chester County Airport Rhode Island Concerned Airport Neighborhoods (CAN) Tennessee Airport Area Residents Alliance Virginia Citizens Concerned About Jet Noise (CCAJN) Washington Airport Communities Coalition (ACC) Citizens Against Sea-Tac Expansion Citizens Fed-Up with Aviation Noise (CFAN) Regional Commission on Airport Affairs Seattle Council on Airport Affairs States with no groups identified Arkansas, Connecticut, Delaware, Idaho, Iowa, Kansas, Louisiana, Maine, Maryland, Michigan, Mississippi, Montana, Nebraska, New Hampshire, New Mexico, North Dakota, Oklahoma, Oregon, South Carolina, South Dakota, Texas, Utah, Vermont, West Virginia, Wisconsin, Wyoming National groups National Helicopter Noise Coalition (NHNC) National Organization to Insure a Sound-Controlled Environment (NOISE) Rural Alliance for Military Accountability U.S.-Citizens Aviation Watch (US-CAW) SOURCE: Noise Pollution Clearing House, 2002. nology that will ultimately reduce the total noise produced by aviation. Currently, much more funding is devoted to local abatement than to research and technology. Also, to avoid raising unrealistic expectations, the federal government should realign research goals with funding allocations either by relaxing the goals or, preferably, by reallocating some noise abatement funds to research and technology. GOVERNMENT GOALS, STRATEGIES, AND POLICIES In 1997, NASA established noise reduction goals: to reduce the perceived noise of future aircraft by 50 percent in 10 years and 75 percent in 25 years. NASA hoped to achieve these goals by advancing technology to TRL 6 three years prior to the desired date, assuming that would be enough
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For Greener Skies: Reducing Environmental Impacts of Aviation FIGURE 2-6 NASA technology readiness levels. SOURCE: NASA, 2000. FIGURE 2-7 Federal investments to reduce source noise (in millions of constant year 2000 dollars). SOURCE: Lukachko and Waitz, 2001.
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For Greener Skies: Reducing Environmental Impacts of Aviation FIGURE 2-8 Federal investments in noise abatement (Airport Improvement Program and Passenger Facility Charge Program expenditures in millions of constant year 2000 dollars). SOURCE: Lukachko and Waitz, 2001. FIGURE 2-9 Ratio of federal funds spent on local noise abatement projects (soundproofing of homes, etc.) to funds spent by the FAA and NASA on noise research and technology. SOURCE: Lukachko and Waitz, 2001.
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For Greener Skies: Reducing Environmental Impacts of Aviation FIGURE 2-10 Historical trends in aircraft noise compared with NASA’s noise goals. Centerline takeoff noise for aircraft certificated since 1980 is typically about 4 dB louder than sideline noise during takeoff and about 8 dB louder than approach noise. SOURCE: Lukachko and Waitz, 2001. time for industry to incorporate the new technology into operational aircraft. Given past history, a 10-year transition period is more realistic. Also, even if new aircraft entering service are quieter, the average noise level is driven by existing aircraft, because they are noisier and more numerous. These older, noisier aircraft may remain in service for 30 years or more. Eventually, however, achieving NASA’s technology goals could reduce noise enough at many airports so that a DNL of 55 dB would not be exceeded outside the airport property limits. This level is currently believed by many to be an “acceptable” intrusion into daily life and is consistent with current EPA guidelines for acceptable noise exposure for outdoor activities requisite to protect public health and welfare with a reasonable margin of safety. The committee believes that the goal of moving the 55 dB DNL contour within the airport boundary is appropriate for federal technology research and development. However, public willingness to accept aviation noise can change, and even achieving this goal does not guarantee that noise will no longer constrain aviation. Also, NASA’s goals are so aggressive that they represent a significant change in the rate of technological advancement (see Figure 2-10), a change that is unlikely to occur in an environment of decreasing federal research expenditures (see Figure 2-7). A slower rate of technological advance will provide more time for noise restrictions to grow, creating additional limitations on airports’ ability to expand, longer flight delays, and additional expenditures on noise abatement. Programmatic trends in noise research are illustrated by the fate of NASA’s Advanced Subsonic Technology Program. In the noise reduction element of this program, NASA and industry effectively collaborated in accelerating the transition of new technology to commercial products. The program began in 1994 and was on course to achieve its initial noise reduction goals until it was cut short in 2001. NASA had invested about $210 million over 8 years (more than $25 million per year) and produced technology at TRL 5 to 6 that was capable of reducing aviation noise by 8 dB relative to 1992 technology (5 dB relative to 1997 technology). Because of the close collaboration with industry, products employing this technology are already in design, and it is likely that they will be introduced in the market within a few years (i.e., roughly 5 years after the completion of the program). The Quiet Aircraft Technology (QAT) Program, which replaced the noise-related elements of the Advanced Subsonic Technology Program, has a goal of providing technology to allow a reduction of an additional 5 dB (relative to 1997 technology) at TRL 4 in 5 years. The projected budget
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For Greener Skies: Reducing Environmental Impacts of Aviation is $100 million ($20 million per year). The reduction in the TRL goal (from 6 to 4), a direct result of reduced funding, makes it less likely that innovative research ideas will rapidly transition to industrial implementation. More than 60 percent of the funds for the QAT Program will be spent within NASA. NASA funding of noise reduction research by industry, which averaged about $14 million per year with the Advanced Subsonic Technology Program, has been reduced to about $5 million per year with the QAT Program. Because these funds are distributed among many companies, the amount of funding provided to any one company may be insufficient to maintain a critical mass of expertise and research and may be insufficient to attract other internal industry research funds. This could significantly reduce the likelihood that new technology will be adopted and implemented in commercial products. The committee believes that NASA’s technical approach to noise reduction research is well balanced, with 45 percent of funds being expended on engine system noise reduction, 30 percent on airframe system noise reduction, and 25 percent on operational measures to reduce aircraft noise and improve noise-impact modeling. NASA based this allocation on a series of aircraft and aviation system studies and six stakeholder meetings and planning workshops conducted over several years with personnel from FAA, industry, universities, and nongovernmental organizations. The specific objectives of the QAT Program are listed in Table 2-3. Relative to the Advanced Subsonic Technology Program, there has been a shift in the near- versus far-term balance of NASA’s noise reduction research. The QAT Program plans to spend about 10 percent of its funds on near-term research, 40 percent on mid-term research, and 50 percent on far-term research, compared with the Advanced Subsonic Technology Program’s allocation of 20, 70, and 10 percent for near-, mid-, and far-term research, respectively. NASA’s research is appropriately focused on technology for narrow-body twin-engine aircraft, which will constitute most of the future fleet. However, the fleet composition is changing, with greater reliance on regional jets (see Figure 2-11). The increased use of regional jets is of particular interest because these aircraft will bring jet travel and the associated noise concerns to communities not previously affected. Although regional jets provide only about 4 percent of all revenue-passenger-kilometers, they already account for 40 to 50 percent of all commercial aircraft departures in the United States. Regional jets facilitate the scheduling of more direct flights that bypass hub airports (which could reduce traffic at hub airports), but they also tend to stimulate demand on many routes, including routes to and from hub airports (which increases traffic). In the long term, the increased availability of regional jets will probably result in unexpected changes in noise and emission trends. NASA’s limited research portfolio, however, is not well positioned to predict the effects of or respond to changes such as this. TABLE 2-3 Goal, Objectives, and Approaches for Elements of NASA’s Quiet Aircraft Technology Program Program goal Develop to TRL 4 those technologies necessary to achieve NASA’s 10-year noise reduction goal and identify technologies necessary to achieve the 25-year goal Objectives Reduce community noise impact by 5 dB Develop framework to identify technologies for an additional 10 dB reduction Improve source noise models Challenges Reduce engine system noise (4 dB) Reduce airframe system noise (4 dB) Enable low-noise operations (2 dB) Improve physics-based source noise prediction Enable real-time impact modeling Approaches Component diagnostic laboratory experiments Computational aeroacoustics and fluid dynamics Definition and verification of low-noise operations Air traffic management simulations with controllers and pilots Realistic propagation effects FAA’s noise-related research focuses on system-level noise impact assessment tools, such as the Integrated Noise Model (INM) and the Model for Assessing the Global Exposure to the Noise of Transport Aircraft (MAGENTA). These models are used for noise compatibility planning and for assessing various policy scenarios. The models have considerable leverage: they have guided FAA expenditures of $4.9 billion over the past 20 years as well as $4 billion to $6 billion in capital investment by industry during the 1990s. Unfortunately, the FAA does not have clearly articulated metrics or goals for these models, and thus there is no convenient way to measure the FAA’s progress or the appropriateness of its modeling research. The White House Commission on Aviation Safety and Security recognized the importance of these models, recommending in its final report (1997) that the FAA “develop better quantitative models and analytic techniques to inform management decision making,” and urged the FAA “to strengthen its analytic and planning tools, especially through the development of models that give insight into the systemwide consequences of alternative courses of action.” Executing these recommendations requires coordination between the FAA (the user and maintainer of the models) and NASA (which provides much of the science that leads to improvements in the models). The principal coordinating body for the two agencies (as well as for the DoD) is the Federal Interagency Committee for Aircraft Noise. The interagency committee facilitates information sharing, but its ability to act as a coordinating body is constrained by the limited authority of its membership. The interagency committee could be stronger and more effective if agencies appointed as rep-
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For Greener Skies: Reducing Environmental Impacts of Aviation FIGURE 2-11 Changes in the composition of the U.S. commercial fleet, 1994 to 2011. SOURCE: Rolls-Royce, 2001. resentatives personnel with budgetary authority within their home organizations. The Committee on Aeronautics Research and Technology for Environmental Compatibility concludes that federal programs and policies for research and technology aimed at addressing aircraft noise are not sufficient to alleviate aircraft noise as a potentially significant barrier to the growth of aviation. While the noise reduction goals of the federal programs for research and technology development are appropriate, the level of technical activity is insufficient to achieve the goals in the planned time periods and it is likely that noise constraints will continue to impede aviation’s growth and contributions to the national economy. Finding 2-3. Achieving Noise Reduction Goals. Additional technological advances now possible could move most objectionable noise within airport boundaries. However, the goal is unlikely to be achieved by NASA’s target date of 2022, and achieving the goal may not fully alleviate the constraints that noise places on the aviation industry because of potential changes in the public’s perception of the importance of a low-noise environment to quality of life. Finding 2-4. Major Impediments. The most significant impediments to reducing the impact of aviation noise (or emissions) include long-term growth in the demand for aviation services, long lead times for technology development and adoption, long lifetimes of aircraft in the fleet, high development and capital costs in aerospace, high residual value of the existing fleets, and low levels of research and development funding. Recommendation 2-2. Technology Maturity and Scope. NASA and other agencies should sustain the most attractive noise reduction research to a technology readiness level high enough (i.e., technology readiness level 6, as defined by NASA) to reduce the technical risk and make it worthwhile for industry to complete development and deploy new technologies in commercial products, even if this occurs at the expense of stopping other research at lower technology readiness levels. NASA and the FAA, in collaboration with other stakeholders (e.g., manufacturers, airlines, airport authorities, local governments, and nongovernmental organizations), should also support research to accomplish the following: Establish more clearly the connection between noise and capacity constraints. Develop clear metrics for assessing the effectiveness of NASA and FAA noise-modeling efforts. Implement a strategic plan for improving noise models based upon the metrics.
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For Greener Skies: Reducing Environmental Impacts of Aviation Harmonize U.S. noise reduction research with similar European research. Recommendation 2-3. Interagency Coordination. Interagency coordination on aircraft noise research should be enhanced by ensuring that the members of the Federal Interagency Committee for Aircraft Noise have budget authority within their own organizations to implement a coordinated strategy for reducing aviation noise. REFERENCES Boeing. 2001. Growth in world airport restrictions. Available online at <http://www.boeing.com/assocproducts/noise/summary.htm>. FICON (Federal Interagency Committee on Noise ). 1992. Federal Interagency Review of Selected Airport Noise Analysis Issues. August. Fleming, Gregg. 2001. FAA Integrated Noise Model. U.S. Department of Transportation, Volpe National Transportation Center. GAO (General Accounting Office). 2000. Aviation and the Environment— Results from a Survey of the Nation’s 50 Busiest Commercial Service Airports. August. Washington, D.C.: General Accounting Office. Lukachko, S., and I. Waitz. 2001. Environmental compatibility of aviation graphs. Cambridge, Mass.: Massachusetts Institute of Technology Gas Turbine Laboratory. NASA (National Aeronautics and Space Administration). 2000. Quiet Aircraft Technology Workshop. Dallas, Texas. April 11-12, 2000. NASA Office of Aerospace Technology. Available online at <http://www.aerospace.nasa.gov/library/encompat/qat/willshire/sld021.htm>. February 6, 2002. Noise Pollution Clearing House. 2002. Related sites: noise organizations (listed by area of focus). Available online at <http://www.nonoise.org/resource/related/source.htm#Airport%20and%20Aviation%20Noise>. Rolls-Royce. 2001. Aviation market forecast 1994-2011. Indianapolis, Ind.: Rolls-Royce Corporation. White House Commission on Aviation Safety and Security. 1997. Final Report to President Clinton. Washington, D.C.: The White House. Available online at <http://www.fas.org/irp/threat/212fin~1.html>. February 6, 2002.
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