Which of the following is NOT classified as controlled airspace?

Controlled airspace is defined as airspace of defined dimensions within which air traffic control service is provided to protect aircraft operating under Instrument Flight Rules (IFR) and to separate IFR traffic from Visual Flight Rules (VFR) traffic.

Classes A, B, and C are all types of controlled airspace. Class A airspace exists at higher altitudes and is all IFR; Class B airspace surrounds major airports and requires specific clearance to enter, while Class C airspace, which typically surrounds smaller airports, requires communication with air traffic control but has less stringent requirements than Class B.

In contrast, Class G airspace is classified as uncontrolled airspace. This means that there are no air traffic control services provided to separate aircraft operating in this airspace, allowing pilots to operate without the need to communicate with air traffic control unless they choose to or need to for safety reasons. Thus, identifying Class G as not being part of controlled airspace is accurate because it operates under different regulations and guidelines than the other airspace classes.