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Aviation History
1976
1976 - 0286.PDF
402 AIR TRANSPORT pact around JFK and Dulles. Around JFK in 1978, the EIS projects that 485,000 people will reside within the NEF 30 contour and 112,000 within the NEF 40 contour. If four Concorde flights are added to that projection, 487,000 people will reside within the NEF 30 contour and 114,000 within the NEF 40 contour.1 Thus, approximately 2,000 additional people could come within each contour area around JFK, an increase of 0-4 per cent within the NEF 30 area and about two per cent within NEF 40, as the result of the proposed Concorde operations. All 487,000 residents would be exposed to slightly greater total noise exposure (roughly 0-3 NEF units). Thus, at JFK, an already severely affected area would be further degraded, but relatively little compared to the existing levels of noise exposure. Around Dulles, the population is relatively sparse. The EIS projects that less than 1,000 residents will be included within the NEF 30 contour around Dulles in 1978, and no residents will be included within the NEF 40 contour. The addition of the proposed two Concorde daily flights at Dulles would not greatly increase the number of people within either of these contours, although four additional square miles would be included in the NEF 30 contour and less than one additional square mile in the NEF 40 contour. On the basis of the NEF data, the effect of the proposed Concorde operations at Dulles will be hardly perceptible.5 It is left to me to translate these data into a form that can help guide the decision which I make today. This is no easy task. The noise analysis is quite complete and yet it gives me no clear direction. The cumulative noise descrip tor shows that the increase in the number of people who live in the NEF 30 area at JFK would constitute substan tially less than one per cent of those currently exposed to NEF 30. At the same time, the cumulative noise figures show that hundreds of thousands of people would find that they lived in a somewhat noisier environment. The single event contours indicate that the Concorde is a great deal louder than most existing subsonic transports, yet the Con- FUGHT International, 21 February 1976 duration of that event. EPNdB should not be confused with the A-weighted sound level in decibels (dBA), which is com monly used to measure surface transportation and com munity noise levels. A-weighted sound level applies a single frequency-weighted correction to sound pressure level, and does not include the time factor. There is no constant equiva lence between EPNdB and dBA, because of the differences in frequency weightings and time-duration considerations. For the Concorde in level flight at an altitude of about 7,000ft, the difference is approximately 15 units (i.e., 85 dBA equals 100 EPNdB). The FAR 36 measurement values for the Con corde and several subsonic long-range aircraft are cited in p. VI-7-8 of the EIS. B-707-300 Take-off Sideline Approach 119-5 EPNdB 112-0 116-5 113 EPNdB 102 118 An increase of ten EPNdB represents an approximate doubling of the perceived loudness of aircraft noise. The noise levels are not additive. Two noise sources simultaneously producing 100 EPNdB do not combine to produce 200 EPNdB. In fact, the increase in noise would barely be perceptible to the human ear. :i The EIS included single-event noise contours for 100 and 110 EPNdB noise levels. There is no generally accepted standard by which community reaction may be predicted for a particular level of noise; however, some surveys indicate "acceptable" for repeated exposures. Other surveys indicate that, for infrequent events, a peak level of 100 EPNdB is acceptable. These conclusions, however, are not unani mously accepted. 4 Using the NEF concept of community reaction to aircraft noise exposure, the following interpretations of NEF values have been generally accepted: Less than NEF 30: Essentially no complaints expected; noise may interfere with community activities; NEF 30 to NEF 40: Individuals may complain; group action possible; Greater than NEF 40: Repeated vigorous complaints expected; group action probable: NEF 45: Threshold of possible hearing loss after daily exposure over 40-year period, assuming eight-hour outdoor exposure with the other 16 hours away from area or inside building with at least 15-decibel sound attenuation. corde will conduct only four flights—eight operations—per day into JFK, out of a current daily average total of nearly one thousand operations at this airport.6 1 Since the initial release of the EIS, the results of vibration measurements near Heathrow and Charles de Gaulle Airports have become available. These measurements indicate that structural vibrations induced by Concorde departures and approaches were only twice (not five times) those induced by conventional subsonic aircraft operated along the same flight paths. These comparisons also indicated that certain subsonic aircraft—specifically, the VC10 and the Trident— induced greater levels of vibration than those aircraft more common to the United States airports such as the B-707 and the DC-8. A comparison of these effects with those of the United States aircraft indicates that Concorde-induced struc tural vibrations are three to three and one-half times those induced by long-range subsonic aircraft. The results lend further support to the conclusion of the EIS that structural vibrations which may be induced by the noise of the Con corde will be well below accepted criteria which would pre dict no damage, but may be briefly perceptible to building occupants. 2 Under the standardised procedures specified in FAR 36, aircraft noise is calculated in units of Effective Perceived Noise Level in decibels (EPNdB). This value, which was established as the best representation of human reaction to aircraft noise, factors into the calculation the relative "noisi ness" or "annoyance" of an aircraft noise event and the time Tap of col 2 Potential hearing loss is barely measurable and only in less than 4 per cent of the exposed population at NEF 45. 5 The above comparisons assume that no additional noise abatement measures are taken to reduce the extensive aircraft noise problem. If additional noise-abatement measures prove practicable, the comparisons of incremental Concorde noise impact will alter. If, for example, all sub sonic turbojet aircraft over 75,0O01b were retrofitted with sound-absorbent material, the noise comparisons would change, if retrofit were implemented completely in 1978 (technologically impossible but useful for comparison) the Concorde EIS projected that only 252,000 people would reside within the NEF 30 contour around JFK, and only 30,000 within the NEF 40 contour, a substantial reduction from the "no-retrofit" situation. The proposed addition of four Con corde flights would then result in 261,000 residents within NEF 30 and 30,000 residents within NEF 40 contours. Nine thousand additional people would come within the NEF 30 area around JFK, as the result of the proposed Concorde operations, and all 261,000 residents would be exposed to somewhat greater total noise exposure (roughly 1-0 NEF units). Thus, although the cumulative noise around JFK with the retrofit of subsonic jets, even with the addition of Con corde, would be substantially less than it is now without Concorde, the additional impact of four Concorde flights would be greater than it would be without retrofit. B To clarify the context in which we are operating, I might note that an air carrier could, without amending its opera tions specifications, increase the total noise around an airport more than it will be increased by the proposed Concorde flights simply by adding a few extra flights by, say B-707s or DC-8s.
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