Which of the following is NOT considered controlled airspace?

Controlled airspace is defined as airspace where air traffic control (ATC) has the authority to provide air traffic services to aircraft operating within that space. This includes Class A, Class B, Class C, and Class D airspaces, all of which are regulated environments with specific requirements concerning pilot communication and aircraft operations.

Class A airspace extends from 18,000 feet MSL up to FL 600 and requires pilots to operate under Instrument Flight Rules (IFR). Class B airspace surrounds major airports and consists of various layers that require ATC clearance to enter. Class C airspace is found around airports with a certain level of air traffic and also mandates communication with ATC before entry. Class D airspace is typically present around smaller airports and requires two-way radio communication with ATC.

Class G airspace, however, is considered uncontrolled airspace. In this type of airspace, pilots have the freedom to operate without ATC clearance and can either fly under Visual Flight Rules (VFR) or IFR without the same level of requirements or structure that governs controlled airspace. Thus, Class G represents a more permissive and less regulated portion of the airspace system, which is why it is not categorized as controlled airspace. Understanding