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Aircraft Overflight Study
by Paul Matzner

There is good news on the conservation front for preservation of quietude in natural areas. By the end of this year, the National Forest Service will release a study on the impact of aircraft overflights on wilderness and visitors, and in 1993 the National Park Service will release a similar study. The studies were mandated by Congress in the National Parks Overflight Act, passed in 1987 (PL 100-91).

These studies present the first opportunity for national input on this important conservation issue. It is crucial that we, as nature sound recordists, and others sensitive to nature sounds in pristine areas, contribute to this debate. A condensed version of the press release from the Interagency Aircraft Overflight Sound Study is presented below, with some additional comments afterward. It is imperative that Nature Sounds Society members and other interested persons become involved in this issue if we are to preserve our natural quietude. The best way to do this at this time is to add yourself to the mailing list described at the end of this article.

Overflight Study

[The following is excerpted from "Interagency Aircraft Overflight Sound Study," USDA Forest Service and USDI National Park Service, press release April 10, 1989.]

"The National Parks Overflights Act of 1987 (Pl. 100-9l) requires the Forest Service and the National Park Service to conduct studies of aircraft overflights which may be impacting wilderness and park visitors or resources.

The Act contains provisions to establish regulatory restrictions on overflights at Yosemite, Haleakala and Grand Canyon National Parks, and requires the Federal Aviation Administration to review current aircraft activity over the Boundary Water Canoe Area. It also requires the Park Service to submit recommendations to Congress for minimum altitudes (or other actions which may be necessary to mitigate overflight impacts) over park land. The Forest Service only has to report study results, and is not required to make recommendations.

Existing FAA regulations provide restrictions on minimum flight altitudes at the Grand Canyon, Haleakala and Yosemite National Parks and the Boundary Water Canoe Area Wilderness. The FAA has also issued an advisory recommending no flights below 2,000 feet above ground level over all Park Service areas, designated wildernesses, and other noise sensitive areas.

Areas to be studied are the measurement of background and aircraft sound in natural environments, the relationship of aircraft sound to enjoyment of wilderness visitors, the definition of "adverse impact" and the need to build more effective relationships with other agencies.

The joint study will address two primary goals: 1) Are aircraft overflights impacting wilderness values in Forest Service wildernesses? If so, to what extent? 2) Has the natural quiet been restored at Grand Canyon National Park, following implementation of Special Federal Aviation Regulation 50-2?

The first phase is designed to determine the scope of the problem and gather information to select study sites. Existing aircraft sound levels at Grand Canyon National Park will be measured, and a review of existing literature on aircraft sound levels will be made.

The second phase is designed to identify the most important attributes of the aircraft overflight problem which should be subject to intensive field study. Virtually no previous work has been accomplished in the investigation of aircraft overflight effects on dispersed recreationists in natural settings. There are a tremendous number of variables that influence the impacts of aircraft overflights on wilderness values, including aircraft type, purpose of use, altitude, sound characteristics, and visitor characteristics. Due to the high cost associated with field data collection, the number of variables to be investigated in the field portion of the study will be limited.

The final phase consists of field studies to simultaneously gather sociological and acoustical data, and preparation of final reports.

Due to the complexity and technical difficulty of this study, a Technical Review Group has been established to provide input to the team members for the duration of the study. This group includes technical experts in the fields of psychoacoustics and acoustical engineering, as well as representatives from wilderness user groups and aircraft operators. The group will meet periodically to review progress and products developed."

Additional Reactions

I have already talked with Bill Makel, National Coordinator of the Overflight Study, and have sent him our various articles related to this issue. The Overflight Act has already set minimum altitudes for flights over three national parks at 2000 feet above ground level. The FAA has also issued an advisory recommending that flights over Forest Service or Park Service wilderness be above this level. But, as we have documented in this newsletter in the past, jet planes at altitudes of 20,000 feet are a definite intrusion and make nature sound recording and quiet listening impossible.

Quietude (referred to as "natural quiet") is recognized here for the first time as a natural resource requiring management. Their definition of quietude, however, as "any man-made sound that intrudes on the natural background sound of a wilderness" is problematic. The study team seems to assume that aircraft overflights will intrude on people and their wilderness experience only if heard or "detected." Preliminary surveys at wilderness areas heavily impacted by aircraft show that less than half of the visitors even report hearing the noise. We are fully aware of the insensitivity of most of the urban based population to noise. Urban insensitivity should not be the basis of an average definition. A more comprehensive and absolute definition of quietude in scientific terms is needed.

Measurement of noise will also be relative. The Study group is contemplating using a relative measurement of aircraft noise called "Overall Average Background Level." Thus, if running water sound or even personal noise (called "self noise") is high, the value of a noisy aircraft will be considered as less intrusive. It is unclear how these baseline measurements will be defined and used to determine the "natural quietude" of a particular area, but it may inject bias and downplay the magnitude of noise from aircraft passing over. No absolute measure of quietude seems to be envisioned here. The measurements that are made, and the way these measurements are used, will be crucial determinants in whether quietude is protected.

The study concentrates almost exclusively on the effects of noise on recreational uses, and does not study the effects on wildlife. The group feels that measurements of impact on wildlife are very expensive, and are not mandated by the study. Public response so far has been low. Bill Makel reports that only three hundred people have put themselves on the study's mailing list. The study group seems to interpret this as a lack of interest or priority. I believe that the reason is the lack of visibility and coverage of this study. I only learned about it last November, even though it had been in progress since 1987.

In summary, it is urgent that we express public support of this study and inform ourselves of its progress. To add yourself to the mailing list and receive periodic updates, please write to: Mr. Bill Makel, National Coordinator for Wilderness Aircraft Overflight Study, San Dimas Technology and Development Center, 444 East Bonita Ave, San Dimas, CA 91773 (Phone 714-599-1267, FTS 793-8000). For the Park Service study, write: Mr Steve Hodapp, Wilderness (Coordinator, National Park Service, P.O. 37127, Washington, D.C.20013-7127, (Phone 202-343-5211, FTS 343-5211). Paul Matzner is Chair of the NSS.

The upcoming NSS Handbook will have extensive information on quietude, including copies of previous articles,the text of the Overflight Act, and the quarterly study group updates. If you are not yet a member, fill out the membership form on page 15 to receive this valuable resource.

Articles from Spring 1991

  Point Reyes National Seashore: Thundering Skies

Quiet Places: Aircraft Overflight Study

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