Which of the following is a limitation under Part 161?

Under Part 161 of the Title 14 Code of Federal Regulations, a significant limitation is the establishment of direct limits on cumulative noise exposure around airports. This regulatory framework is designed to manage and control the impact of airport-related noise on surrounding communities. Specifically, it allows for noise compatibility assessments and enables airport operators to implement measures that limit the noise exposure experienced by local residents.

The focus on cumulative noise exposure reflects the understanding that noise impacts from multiple sources, including aircraft operations, can accumulate and affect community quality of life. This means that airports must actively monitor and manage noise levels, providing a structure for addressing community concerns and being held accountable for the noise produced.

In contrast, options such as increasing flight numbers, expanding airport operating hours, or allowing unrestricted aircraft operations do not inherently involve direct regulatory limitations under Part 161. Instead, these actions may contribute to increased noise levels and could lead to community complaints or conflicts, but are not specifically framed as limitations by the regulations. Hence, the regulation's intent is to promote better community relations through concrete limits on noise exposure rather than leaving it entirely unrestricted or unregulated.