What primarily determines the upper limits of Class G airspace?

The primary determinant of the upper limits of Class G airspace is the base of overlying controlled airspace. Class G airspace, also known as uncontrolled airspace, extends from the surface up to the lower limits of the controlled airspace above it. This means that Class G airspace exists until you reach the altitude where the next type of airspace begins, which is typically Class E airspace or higher, depending on the location and regulatory environment.

Understanding this distinction is crucial for pilots and air traffic controllers because it helps delineate areas where visual flight rules (VFR) operations are most likely to take place. In Class G airspace, pilots do not have the same level of air traffic control service as in controlled airspace, which further emphasizes the importance of knowing where Class G transitions into controlled airspace.

While height of the terrain and local regulations can influence operations within Class G airspace, they do not establish its upper limits. Similarly, air traffic volume can impact flight operations but does not define the jurisdictional boundaries of this airspace class. Thus, the base of the overlying controlled airspace is the key factor in determining where Class G airspace ends.