Which airspace category requires approval for operations but does not totally prohibit access?

The category of airspace that requires approval for operations but does not entirely prohibit access is restricted airspace. This type of airspace is designated for specific purposes, such as military training or activities that could pose a danger to non-participating aircraft. While access is not completely denied, pilots must receive permission from the controlling agency to enter the restricted area. This ensures that operations within that airspace can be conducted safely, as the activities occurring there could potentially interfere with or endanger other flights.

In contrast, Class B airspace, which requires specific protocols and clearances for access, is more about stringent access control to ensure safety around busy airports. Class E airspace has no special restrictions and is often used for air traffic control services in various conditions, while Class F airspace is not universally recognized as it can vary by country. Thus, restricted airspace stands out as the type that allows access contingent upon approval.