What is classified as a significant change in noise exposure by FAA?

The classification of a significant change in noise exposure by the FAA is based on established thresholds that take into account the Day-Night Average Sound Level (DNL). The specific choice indicating that an increase in DNL of 1.5 if above 65 dB is recognized as significant aligns with the FAA's guidelines for determining the impact of noise on communities surrounding airports.

In this context, the DNL scale is a critical metric used to assess long-term noise exposure, and the values provided in the various options are designed to reflect the thresholds beyond which a noticeable impact on community noise levels is experienced. An increase of 1.5 DNL is a substantial change since it reflects a considerable shift in how noise can affect population areas, particularly as it relates to sleep disturbance and general quality of life which are major concerns around airport operations.

In contrast, the other options propose increases that either do not meet the FAA's criteria for significance or are lower than what is deemed necessary to warrant adjustments in operational or mitigation measures. Thus, the correct answer reflects the FAA's standard for what constitutes a significant change in noise exposure due to aviation activity.