Which airports have slots allocated to scheduled air carriers and commuters?

High-density airports are specifically designated as locations where the volume of air traffic is significantly high, necessitating the allocation of slots to manage the flow of aircraft safely and efficiently. These slots refer to the rights for airlines to take off or land at specific times. The purpose of this allocation system is to reduce congestion and enhance safety at busy airports, thereby ensuring that scheduled air carriers and commuter services can operate within a structured framework.

In contrast, other options like all airports in the United States do not require a slot allocation system because many airports operate without the same level of congestion. Private airfields often accommodate general aviation but do not have the same regulatory requirements for slot allocations as commercial airports. Rural airports typically serve fewer flights, thereby reducing the need for a slot allocation system. Hence, the correct focus on high-density airports acknowledges the significant operations and traffic challenges they encounter, which necessitates a structured approach to managing airspace and ensuring airlines can operate efficiently.