Which reference is primarily used to determine if airspace is controlled or uncontrolled?

Sectional aeronautical charts are the primary reference for determining whether airspace is controlled or uncontrolled. These charts provide detailed information about various types of airspace and their classifications, including Class A, B, C, D, and E airspaces, as well as uncontrolled airspace.

Sectional charts visually depict the boundaries of different types of airspace, indicating areas where air traffic control services are provided versus areas where pilots have more freedom to operate without ATC communication. Additionally, these charts include important aeronautical information such as airports, navigation aids, and topographical features, which enhance situational awareness for pilots.

While other resources like Air Traffic Control Manuals provide regulatory and procedural information related to air control, they do not visually represent the airspace structure like sectional charts do. Similarly, services that provide radar information or flight data recordings are useful for in-flight management but serve different purposes and do not offer a clear depiction of airspace divisions. Thus, sectional aeronautical charts are indispensable tools for pilots in identifying controlled versus uncontrolled airspace.