A dashed blue circle surrounding an airport on a sectional chart indicates which type of airspace?

A dashed blue circle surrounding an airport on a sectional chart signifies Class D airspace. Class D airspace is typically found around airports with operational control towers, and it extends from the surface up to a designated altitude. The dashed blue line visually distinguishes this airspace from surrounding areas, indicating that certain regulations apply, such as the need for pilots to communicate with the control tower when operating within this airspace.

In Class D airspace, pilots must establish two-way communication with the control tower before entering, which is crucial for safety and efficient traffic management around busy airports. The specific features of Class D airspace, such as its size and requirements, are important for pilots to understand in order to navigate safely and comply with regulations. This understanding helps them to avoid airspace violations and enhances overall aviation safety.