What is the key factor that defines whether airspace is considered uncontrolled?

The defining factor that determines whether airspace is categorized as uncontrolled is the presence or absence of air traffic control services. In uncontrolled airspace, pilots operate without the assistance of air traffic controllers, which means they are responsible for their own separation and navigation. This contrasts with controlled airspace, where air traffic control services provide guidance, manage traffic, and ensure safe distances between aircraft.

Air traffic control services are crucial for maintaining order in more congested or complex airspace where traffic might be high or where various types of aircraft operate. Uncontrolled airspace, often referred to as Class G airspace in the United States, allows pilots to operate freely as long as they adhere to basic regulations and maintain visual separation from other aircraft.

While factors such as altitude, specific flight regulations, and the presence of scheduled commercial flights might influence the operational environment, they do not directly define whether airspace is controlled or uncontrolled. The absence of air traffic control services is the key characteristic that distinguishes uncontrolled airspace.