Aircraft noise is currently measured on a scale that
averages all community noise during a 24-hour period,
with a ten-fold penalty on noise that occurs during
night and early morning hours. The scientific
underpinnings for this measurement, known as the
Day-Night Average Sound Level (DNL), were the result of
social surveys of transportation noise in the 1970s.
1981, the FAA established DNL 65 decibels as the
guideline at which federal funding is available for
soundproofing or other noise mitigation. This method was
reaffirmed in studies conducted during the late 1980s
and early 1990s.
During the ensuing years, aircraft manufacturers
incorporated technologies that resulted in dramatically
quieter aircraft. However, residents around many of the
airports have expressed concerns about aircraft noise
associated with the continuing growth of the aviation
industry. The FAA is taking an updated look at its
approach for measuring noise as part of an ongoing
dialogue with stakeholders, including communities and
leaders of a number of cities across the nation.