May 7, 2024July 31, 2026

The basics of noise metrics

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Burien Airport Committee

This document explains how aircraft noise is measured using decibel-based metrics such as DNL, CNEL, and SEL, and highlights that the FAA's accepted noise threshold of 65 dB exceeds the World Health Organization's recommended limits of 50–55 dB outdoors and 30–35 dB indoors. It also notes that standard metrics like SEL fail to capture the cumulative impact of repeated aircraft overflights. The international aviation body ICAO recommends a four-part 'Balanced Approach' to managing airport noise, encompassing noise reduction at the source, land-use planning, operational procedures, and operating restrictions.

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This document from Sky Posse Palo Alto explains environmental noise measurement using dBA metrics, covering both single-event metrics (Lmax, SEL) and average noise metrics (Leq, LAeq, DNL, CNEL). It also addresses the limitations of SEL in capturing repetitive aircraft noise exposure and compares FAA noise thresholds to WHO guidelines for community noise in specific environments.

As the source for federal transportation grants, the Puget Sound Regional Council was charged with developing a system to meet the growing need for commercial aviation. When the search for a second airport failed, they authorized the Port of Seattle to build the Third Runway, with a mandate to develop a noise abatement and mitigation program. In their effort to stop the Third Runway, the ACC argued over every detail of the Port's efforts--including property buyouts and sound insulation. The dispute was meant to be settled by a three member Expert Arbitration Panel. This is their final report. It finds 2-1, that the Port's program was insufficient in several respects. Despite that, funding for the Third Runway was approved by the PSRC, and the 'Port Package' program, proceeded largely unchanged. Expert Arbitration Panel's final decision finding that the Port of Seattle had not shown sufficient reduction in real on-the-ground noise impacts to satisfy noise reduction conditions required for approval of a third runway at Sea-Tac International Airport. The majority decision concluded the Port's noise abatement programs were insufficient despite being impressive in scope.

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