Which type of airspace has a ceiling defined in AGL terms?

Class E airspace is characterized by its unique definition, which includes a ceiling measured in terms of above ground level (AGL). This distinguishes it from other classes of airspace, which typically have their ceilings defined in terms of mean sea level (MSL). Class E airspace can extend from a specified altitude up to the base of the overlying airspace, which may be Class A or higher.

This ability to define the ceiling in AGL terms is crucial for pilots flying at lower altitudes, as it provides a clearer understanding of their altitude in relation to the ground and surrounding terrain. This is particularly important when navigating near airports or under other controlled environments where the topography can significantly impact flight operations.

In contrast, Class D, Class C, and Class B airspaces generally have their ceilings defined at a specific MSL altitude, making them less flexible in terms of ground reference. This structural difference is a key feature that pilots must be aware of when planning their operations within the NAS.