The FAA believes that airport operators must own all property within which DNL contour?

• A. 60 DNL
• B. 75 DNL
• C. 65 DNL
• D. 70 DNL

Answer: (B)

The key idea is that noise exposure around an airport is measured in DNL (Day-Night Average Sound Level) contours, which show how loud the area is over a year. The FAA uses a 75 DNL contour as the boundary for many land-use and noise-mitigation actions because areas inside this contour experience significant and disruptive noise. When an airport sponsor owns all property within this boundary, it can implement consistent mitigation measures—like sound insulation, property acquisition, or land-use controls—without conflicts with private owners and with greater certainty that future development won’t undermine the mitigation efforts. This ownership helps ensure the airport can effectively manage noise impact and protect residents and plans.

Other contours represent different levels of noise exposure and planning triggers, but they’re not the standard boundary the FAA requires for property ownership around the airport.