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Final Environmental Assessment for Proposed Arrival Procedures to Seattle-Tacoma International Airport: Appendix F — Noise and Its Effects on People

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Greener Skies

This document explains the noise metrics used to evaluate aircraft noise around Seattle-Tacoma International Airport, including decibels (dB), A-weighted decibels (dBA), and the Day-Night Average Sound Level (DNL). It describes how sound is measured on a logarithmic scale, meaning noise levels don't add up the way ordinary numbers do, and explains why A-weighted measurements are the standard used by the FAA and EPA because they best match how human ears perceive sound. These concepts form the technical foundation for assessing the environmental impact of proposed flight arrival procedures at Sea-Tac.

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Notes

Appendix F of the Final Environmental Assessment (EA) for proposed arrival procedures to Seattle-Tacoma International Airport, prepared by Greener Skies, dated 1 November 2012. Covers acoustic metrics used in FAA Order 1050.1E environmental impact analysis: decibel (dB), A-weighted decibel (dBA), Sound Exposure Level (SEL), Equivalent Sound Level (Leq), and Day-Night Average Sound Level (DNL). Explains logarithmic nature of sound pressure level (SPL), A-weighting filters (A, B, C, D), frequency response characteristics, and common environmental sound levels per FAA Advisory Circular 36-3G. Relevant to Part 150 noise analysis, DNL65 contours, and NEPA environmental review for Sea-Tac Airport arrival procedures.

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