How does the FAA assess overall aircraft noise exposure?

The Federal Aviation Administration (FAA) requires the use of the Day-Night Average Sound Level (DNL) as the primary metric for aircraft noise exposure. DNL is not a typical average, but instead is a cumulative measure of all noise exposure during a 24-hour period, whether it is a loud event or a quieter event, which increases the DNL value. To reflect the added intrusiveness of noise between nighttime hours of 10 pm-7 am, DNL accounts each nighttime noise event as if it occurred 10 times. FAA noise evaluations typically average daily DNL values over a one-year period to account for daily or seasonal fluctuations in aircraft operations, runway use, and weather conditions. FAA considers all residential land use to be incompatible with aircraft noise at an annual-average exposure levels at or above DNL 65 decibels (dB).