Knowledgeable observers of Northwest Airlines were not surprised by their back-door deal with Senator Lott (R, Mississippi) to try to prohibit use of some Federal funds for noise mitigation in Minnesota. The insulation program was agreed to as part of a 1995 arrangement with Minneapolis for their support of MSP expansion. And, although Metropolitan Airport Commission Chair Vicki Grunseth wrote "the process stank" and the bad effect was a "great deal on trust," she admitted MAC needed to use passenger facility charge revenue and airport revenue for an extended noise mitigation program, and it could be a budget problem.
SMAAC thinks it was a small mishap in a large national campaign by the major airlines to have "a great effect" on airport noise regulation. Chair Grunseth didn't mention that FAA may permit, or MAC may plan, using PFC funds only after noise mitigation is completed for more impacted areas, such as high-noise areas associated with projected use of new runway 17-35. She didn't mention that MAC just decided to plan on less PFC revenue and more noise abatement by accepting, without question, Northwest's statements about retiring their noisiest planes before 2007. This depends a great deal on trust that noise exposure is not being understated and under-budgeted again. SMAAC thinks, based on the flights actually made compared to prior projections, the MAC's trust is misplaced, at least; perhaps unduly influenced.
MAC is preparing an updated noise control plan that skips at least 3 updates (audits) required by FAR 150, and has a precedent that projected noise exposure maps exclusively determine eligibility for noise mitigation even if they are arbitrary and unaudited. SMAAC challenged MAC to produce the baseline (audit) maps for 1996, 1998, or 2000 actual fleet-mix and use of MSP. Without these updates, FAA can as easily interpret that under-65-D NL areas were treated "illegally" as that some between 64 and 60 DNL areas, as mapped in 1992, are near or over 65 DNL now. What interpretations do you think the major airline lobbyists and their Senator friends are urging FAA to make? What will be the political and legal effect of publishing a projected-for-2007 DNL map and SIP budget next Spring?
Knowledgeable observers of Northwest Airlines lobbyists and PR consultants also were not surprised by Ms. Grunseth's minimization of noise impacts and her misrepresentation of noise exposure. She apparently trusts what she has been told by Northwest, or she gets her misinformation from the same sources. Mayor Rybak's raised and amplified voice could not be heard during overflights at Pearl Park [64 DNL].
If the Integrated Noise Model, valid use assumptions, and reliable projections of noise abatement at the source does define areas where sound insulation reduces airport noise 5 decibels to levels "comparable to two people talking five feet away" [that is, attenuating 65 decibels to 60 decibels sound intensity], why didn't MAC update the 1992 map to 2001 actuals and insulate only up to the 65 DNL? Well, because the 60 DNL contour on the 1992 map was drawn using invalid assumptions and unreliable projections; 5 decibels insulation at the old 60 DNL contour might leave interior noise as loud as a freight train (75 decibels intensity). My physics textbook says loudness cannot be measured by instruments, but it is possible to establish a scale of perceived loudness to sound intensity which can be. Ms. Grunseth refers to such a scale, which was made in a soundproof room [the reported decibel levels, a ratio of intensities, were based on zero other noise in the environment] and on a limited set of frequencies [tones] sensed by db-meter. A "DNL" or computed day-night level is not a comparable sound level or intensity; not a decibel, not even an average decibel level. A "DNL" is a weighted average of event noise or per-overflight noise computed for a 24-hour period using mean average temperature, average aircraft altitude, and aircraft source noise intensity. Event noise is the computed noise exposure on the ground during an overflight. All of this averaging obscures the accuracy of the noise exposure figure a DNL represents, but the "typical" event, if there is one, averages noise intensity over 8 seconds. If the observer is at the 65 DNL contour, the average intensity was computed as 65 +/- 0.05 decibels over zero ambient noise. But the peak intensity, when the aircraft is directly overhead, is at least 85 decibels and often higher. MAC regularly records overflight peak noise at ANOMS stations on its 65 DNL contour with peaks of 99 and 100 decibels over ambient noise. Inside an insulated home the peaks measure 80+ decibels.
The perceived noise scale expresses hearing conditions. The basis for sound-abatement and noise mitigation regulations is not incidental annoyance but real damage. Babies experience pain at sound intensities around 95 decibels. An unexpected noise of 50 decibels can startle people and cause accidents. Repeated exposure to sounds over 75 decibels causes permanent hearing loss. A 40 decibel noise awakens a sound sleeper. A 50 decibel noise masks an approaching automobile completely. A business deal can be confused by noise. Student performance is adversely impacted by low-intensit y, frequent, irregular overflights as proven in a well-known recent study in Munich.
Noise regulations are supposed to be like environmental permit limits. If you plan to abate emissions by source suppression or operational limits as agreed, you are permitted to emit so much without penalty. But if the limits are exceeded, you can be fined or your operations limited. In effect, permit limits were set for MSP noise in the FEIS based on the Noise Control Plan. But the abatement measures were not enforced and operational limits were not set and excess noise is unmitigated. The public trusted MAC and FAA; MAC trusted the airlines.
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