National Academies Press: OpenBook

Helicopter Noise Information for Airports and Communities (2016)

Chapter: Chapter Three - Community Response to Helicopter Noise

« Previous: Chapter Two - Unique Role of Helicopters, Their Complex Noise Characteristics, and the Role of Stakeholders
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Suggested Citation:"Chapter Three - Community Response to Helicopter Noise ." National Academies of Sciences, Engineering, and Medicine. 2016. Helicopter Noise Information for Airports and Communities. Washington, DC: The National Academies Press. doi: 10.17226/23609.
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Suggested Citation:"Chapter Three - Community Response to Helicopter Noise ." National Academies of Sciences, Engineering, and Medicine. 2016. Helicopter Noise Information for Airports and Communities. Washington, DC: The National Academies Press. doi: 10.17226/23609.
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Suggested Citation:"Chapter Three - Community Response to Helicopter Noise ." National Academies of Sciences, Engineering, and Medicine. 2016. Helicopter Noise Information for Airports and Communities. Washington, DC: The National Academies Press. doi: 10.17226/23609.
×
Page 10
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Suggested Citation:"Chapter Three - Community Response to Helicopter Noise ." National Academies of Sciences, Engineering, and Medicine. 2016. Helicopter Noise Information for Airports and Communities. Washington, DC: The National Academies Press. doi: 10.17226/23609.
×
Page 11

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8 ANNOYANCE The adverse impact of aircraft noise is usually expressed in terms of annoyance (that is, a subjective response to a particular sound). Annoyance is gauged by the self-report of reactions in community- wide social surveys, which typically ask residents about their level of annoyance with aircraft noise, ranging from “not at all” to “highly annoyed.” Schultz (1978) and his successors have produced sev- eral quantitative dosage-response relationships to predict the prevalence of a consequential degree of aircraft noise-induced annoyance attributable to cumulative noise exposure. The most commonly cited measure of community annoyance response to noise is the Schultz Curve, which plots the percentage of the population that is highly annoyed as a function of Day-Night Average Noise Level (DNL). The Schultz Curve was based on aircraft, rail, and road noise. Very little information is available concern- ing the annoyance produced by helicopters rather than fixed-wing, rail, or road operations. Dosage-response relationships, such as the Schultz Curve, attempt to predict the prevalence of annoyance in communities from cumulative noise exposure such as DNL. The Schultz Curve accounts for less than half of the variance in the association between noise exposure and annoyance. In other words, there is a wide range in the reported annoyance for a given noise level, indicating that commu- nity annoyance is dependent on more than just the DNL. Only in recent years has a practical, quantita- tive method emerged for incorporating an additional variable into predictions of annoyance prevalence rates. This is described in the next section, where the annoyance prediction accounts for nonacoustic influences on annoyance.1 In the literature, a number of “correction factors” have been suggested for interpreting helicopter noise based on the impulsive nature and/or induced rattle caused by helicopter noise. These factors range from 3 to 12 dB with no clear consensus. Even if it is assumed that the annoyance of exposure to noise produced by helicopters is best understood in entirely acoustic terms, a further question remains: whether that annoyance is pro- duced solely by the airborne acoustic energy that helicopters produce or also by secondary emissions (rattling noises and vibration) induced by helicopter noise in residences. DIRECT ANNOYANCE OF AIRBORNE NOISE CREATED BY HELICOPTERS There is an outstanding question in the research field as to whether a noise metric such as DNL accounts for the way people respond to helicopter noise. In the annotated bibliography (Appendix B) there is discussion of correction factors considered for helicopter noise. Appendix A2 shows that even if other noise metrics such as those that are affected by low-frequency noise are considered, most metrics are highly correlated (note that none of the existing metrics account for impulse type noise). Leverton (2014; see also Leverton and Pike 2007, 2009) suggests that helicopters are per- ceived differently and that nonacoustic factors play a role. Fidell et al. (2011) published a way of measuring the nonacoustic response by comparing communities and identifying the acoustic and nonacoustic part of annoyance response (Appendix A). The Final Draft International Standard of the revised ISO Standard 1996-12 (ISO 1996) adopts this concept of a correction factor by noise source, but does not directly address helicopter noise correction factors. If helicopter noise is more annoying, decibel for decibel, than fixed-wing aircraft noise, perhaps a helicopter-specific annoy- ance dosage-response curve may be developed and an ISO 1996-1 type correction for helicopters may be developed; however, to date no such relationship is known. This is an area where additional research is needed. chapter three COMMUNITY RESPONSE TO HELICOPTER NOISE

9 FAA’s review of the technical literature on the annoyance of helicopter noise in its Nonmilitary Heli- copter Urban Noise Study (FAA 2004) cites eight (mostly laboratory) studies supporting the imposition of a blade slap penalty on A-weighted measurements of helicopter noise and seven suggesting that such a penalty is not justified. The FAA report also cites two studies of heightened reaction to helicopter noise—presumably not associated with blade slap—by Schomer (1983) and Atkins et al. (1983). Based on the inconsistency and ambiguity of these findings, the study concluded that the annoyance of heli- copter noise had not been fully substantiated by a well-correlated metric. As a result, FAA continued to rely on DNL as its primary noise descriptor for airport and heliport land use planning and also contin- ued to use supplemental noise descriptors for evaluation of helicopter noise issues. ANNOYANCE RESULTING FROM SECONDARY NOISE EMISSIONS Inside homes near helipads and helicopter flight paths helicopter operations can induce a noticeable vibration in addition to the noise that penetrates the structure. These are called structural vibrations or secondary emissions, because the vibration is the product of sound waves from the helicopter interacting with the structure of the home. A portion of the energy contained in the sound waves is transferred to the structure and, as a result, the home vibrates. Even modest levels of structural vibra- tion, which might escape direct notice, can cause lightweight or suspended architectural elements that are mounted vertically [e.g., windows, doors, pictures on walls, heating, ventilation, and air con- ditioning (HVAC) ducts, and other vertically mounted household paraphernalia] to rattle audibly.3 Such rattling noises can be annoying in their own right, whether or not accompanied by noticeable vibration or by audible helicopter noise. This is more likely to be a problem with helicopters rather than fixed-wing aircraft, because of the low-frequency content of helicopter noise that is not usually a part of fixed-wing aircraft noise. Research has attempted to quantify the increase in annoyance associated with the induced rattle. Fidell et al. (2002a) showed a relationship between the prevalence of annoyance resulting from air- craft noise-induced rattle and a single event measure of low-frequency noise. In other words, if the helicopter noise induces a rattle, the annoyance response is increased as though the noise were louder than it is. The annotated bibliography (Appendix B) cites a number of papers where this is discussed, and there is general agreement that induced rattle causes higher reported annoyance than if no rattle were to exist at the same noise exposure; however, there is no consensus on the correction factor that may be associated with this induced rattle. The presence of secondary emissions is affected by the type and quality of the home construction as well as maintenance. Aluminum sliding windows of the 1960s are well known for their lightweight, poor fit, and predisposition to rattle. Recent building codes, instituted to reduce home energy consump- tion, have contributed to much higher quality, better fitting windows, with far less tendency to rattle. LABORATORY VERSUS FIELD STUDIES OF HELICOPTER ANNOYANCE Studies of the annoyance of helicopter aircraft noise have been conducted under both laboratory and field conditions. Laboratory studies offer greater control over listening conditions than field studies, but lack the context of field studies. It is also difficult to accurately reproduce recorded or synthesized helicopter sounds under laboratory conditions, while preserving the dynamics of helicopter noise emissions. On the other hand, although field studies provide the appropriate context for annoyance judgments, they lack the precision of control over acoustic conditions of laboratory studies. It follows that questions about potential nonacoustic influences on the excess annoyance of heli- copter noise are not readily answered in laboratory studies and that questions about the detailed acoustic origin of excess annoyance are not readily answered in field settings. Schomer and Wagner (1995b) captured many of the benefits of both methods with their laboratory and field studies in which subjects in real houses compare two real sound sources. One is the source under test, such as a helicopter flyby, and it is compared with the noise of five or six different sizes of passing motor vehicles. The authors also found “that the rate of notice of helicopter noise was three

10 times as great as the rate of notice of fixed-wing aircraft noise.” They speculate that the greater rate of notice of helicopter noise was due to the “distinct sound character” of rotary-wing aircraft. Because the participants were exposed to notably fewer helicopter than fixed-wing overflights, it is also pos- sible that they were less habituated to helicopter noise than to fixed-wing aircraft noise. NONACOUSTIC CONTRIBUTIONS TO COMMUNITY REACTION TO HELICOPTER NOISE FAA, in its Report to Congress: Nonmilitary Helicopter Urban Noise Study (2004) has summarized many operational, situational, and other nonacoustic factors that contribute to the adverse community response to helicopter noise, including low flight altitudes; long hover durations; and the times, num- bers, and frequencies of operations, fear of crashes, and attitudes of misfeasance and malfeasance. With the exception of hover times, these factors similarly affect the annoyance derived from fixed- wing aircraft noise. Helicopters hovering over residences or operating at low altitudes may prompt concerns about the privacy or fear of crashes, which can affect annoyance. Perceptions of the necessity for flight operations can also affect the response to helicopter noise. The necessity of medical evacuation, search and rescue operations, and firefighting is widely acknowl- edged and may make noise from helicopters conducting these missions more acceptable to the com- munities they serve. In contrast, private transportation of individuals by helicopter is widely viewed as a luxury (for example, rich people avoiding road traffic), which may contribute to an increase in annoyance. The ability of helicopters to takeoff from and land at nearly any flat area and to fly on nonlinear routes likewise can affect the level of annoyance. Fixed-wing aircraft near airports necessarily approach and depart runways on flight paths corresponding to runway alignments. Helicopters are not as predict- able in their flight paths and the reason for their operation in a particular area is not always apparent. For example, helicopters may be directed by ATC to hover at a distance from an airport to avoid con- flict with a faster-moving jet aircraft or may be flying at a lower altitude to remain below cloud cover. Because helicopters are slower than fixed-wing, aircraft ATC separates helicopters from fixed-wing aircraft primarily by keeping helicopters at altitudes below the altitudes of fixed-wing aircraft. Given their flexibility of flight, people may wonder why a helicopter is flying close to their homes rather than over water or at a higher altitude. The most common nonacoustic factor discussed in the literature, both for fixed-wing aircraft and helicopters, is fear of an accident. Other factors include the perceived necessity of the operation, pre- dictability of the noise, and habituation and past experience (Harris 1979). Helicopters add a unique nonacoustic factor, which can be perceived as a loss of privacy. It is possible that because helicopters have the ability to hover and are typically kept at lower altitudes than fixed-wing aircraft the effect of fear and loss of privacy is exacerbated. In the airport surveys done as part of this synthesis, inter- viewees reported that communities commonly request that helicopters be flown at higher altitudes. There may be both acoustic and nonacoustic reasons behind this request. COMPLAINTS Complaints are one means through which the community communicates its annoyance with helicop- ter noise. It is important to distinguish between complaints and annoyance. In the field of psycho- acoustics annoyance is considered an attitude and a complaint is considered a behavior. Community attitudes; that is, annoyance, are determined through complicated and expensive social surveys of randomly selected individuals in the community. Community complaints are usually recorded by the local airport. A novel approach to helicopter noise has recently been instituted in Los Angeles and is based on collecting helicopter complaints correlated with flight tracks to help identify patterns and trends in helicopter operations, improve understanding of community reaction to helicopter noise, and inform future efforts to develop and implement noise abatement measures (see http://heli-noise- la.com/). Whether collected regionally or by airport complaint tracking is one measure of community response that many airports find useful. Interpreting the complaint data can be complicated by a number of prolific complainers; therefore, complaint data are often reported and mapped as the total

11 number of complaints and total number of complainers. A recent report identifies interesting patterns in complaints that appear to be common to all airports and that is that for nonprolific complainers there is a fixed ratio of the number of people who complain once, versus twice, three times, etc. (Fidell et al. 2012). In 2007, in response to community concerns, FAA designed a visual flight rules (VFR) helicopter route to reduce noise over communities along the north shore of Long Island by moving flights off- shore and establishing a minimum altitude. FAA published the route on the Helicopter Route Chart for New York, effective May 8, 2008. Subsequently, New York public officials advised FAA that they continued to receive noise complaints in this area even with the voluntary North Shore Helicopter Route in place. In 2012, FAA adopted a rule that made the route mandatory for a trial period of 2 years, on the basis that increasing use of the route by making it mandatory would further reduce noise impacts from helicopters operating along the north shore of Long Island (the rule was subse- quently extended for an additional 2 years). In July 2013, the Federal Court of Appeals for the District of Columbia found that the rule was supported by substantial evidence. The ruling appears to rely con- siderably on evidence of a high number of noise complaints rather than any specific acoustic measure.

Next: Chapter Four - Noise Metrics for Quantifying Helicopter Noise »
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TRB's Airport Cooperative Research Program (ACRP) Synthesis 76: Helicopter Noise Information for Airports and Communities examines the results of a literature review and survey of ten airports to summarize the impact of outreach, helicopter noise management programs, technology, and abatement procedures in managing helicopter noise. The report is geared to assist both airports and communities with addressing helicopter noise and a description of the current state of effective practices for noise management.

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