TagDNL65(24)

This 2022 FAA guidance letter explains how airports can legally spend airport revenue on noise insulation projects, such as new windows, doors, and air conditioning, for homes and schools located within the DNL 65 dBA noise contour — the federal threshold for significant aircraft noise impact. Spending airport revenue on noise insulation for properties outside that noise boundary is generally prohibited as revenue diversion, unless a lower local noise standard has been officially adopted or 'block rounding' has been approved. The letter also clarifies that airports may purchase mobile or permanent noise monitoring equipment using airport revenue, provided certain conditions are met, but monitors cannot be used to enforce noise abatement flight procedures.

This 2021 FAA report analyzes the Neighborhood Environmental Survey (NES), a large-scale study examining how aircraft noise affects communities around 20 U.S. commercial airports. Researchers surveyed over 10,000 residents and found that annoyance with aircraft noise increases steadily as noise levels rise, with significantly more people reporting high annoyance than older studies had suggested. The findings provide an updated national curve showing the relationship between measured noise exposure (DNL) and community annoyance, which can inform airport noise policy decisions.

Currently, FAA law has extremely complicated rules for establishing a noise boundary around airports. (A noise boundary is a geographic area inside which there is a certain acceptable noise level.) This is referred to as the DNL65. and it has several major flaws. The FAA Reauthorization Act Of 2018 attempted to address these flaws in several ways. This letter, from a caucus of Congressmen engaged on airport community issues complains to the Administrator that the spirit of the law is not being adhered to and demands that he make attempts to put his agency into compliance. The language is fairly technical, however there are a couple of basic points they raise: First, that the noise boundary be determined by actual noise measurements (currently the noise boundaries are 'modeled' and those calculations often do not reflect in any way the lived experience for residents.) Second, that the 'acceptable' noise level of sixty five decibels (hence DNL65) has been determined to be far too high to conform with current understandings of healthy living.

This April 2020 FAA Report to Congress evaluates alternative noise metrics to the current Day-Night Level (DNL) 65 decibel standard used to measure community aircraft noise exposure, as required by the FAA Reauthorization Act of 2018. The report reviews the history and definitions of various noise measurement tools, explains why no single metric can address all aviation noise situations, and examines the roles of both noise modeling and actual noise sampling. It was produced in response to congressional direction to assess whether better methods exist for capturing and addressing community concerns about airplane noise.

H.R. 5874, the 'Decrease Noise Levels Act,' introduced in February 2020, would require the FAA to lower the threshold for significant aircraft noise from a day-night average sound level of 65 to 60 decibels. The bill also directs the FAA to publish a public report within one year outlining a strategy to further reduce residential noise levels to 55 decibels over the following decade. Additionally, it mandates that community outreach efforts include evaluations of alternative noise measurement metrics beyond the current standard.