A dashed blue line around an airport indicates what type of airspace?

A dashed blue line surrounding an airport indicates Class D airspace. Class D airspace is typically found around airports that have an operational control tower. The dashed blue line signifies the lateral boundaries of this airspace, which extends from the surface up to a certain altitude (usually 2,500 feet above the airport elevation).

Pilots operating in Class D airspace must establish radio communication with the control tower before entering the area. The dashed appearance of the boundary helps differentiate it from other classifications, as it visually represents the controlled nature of the airspace while also indicating that it does not extend as far above the surface as other classes, such as Class B or Class C, which have solid lines.

In comparison, Class B airspace would be represented by a solid blue line and generally covers larger terminal areas around major airports, while Class C airspace is depicted with a solid magenta line and has a more complex structure. Class E airspace might indicate additional controlled airspace but is not specifically represented by the dashed blue line format.