In which type of airspace are only IFR flights allowed, and requires ATC clearance?

The correct answer is the airspace classified as Class A. This type of airspace extends from 18,000 feet up to and including 60,000 feet, and is designated for Instrument Flight Rules (IFR) operations only. In Class A airspace, all pilots must operate under IFR, and ATC clearance is mandatory for any flights entering or navigating within this airspace.

Class A airspace is specifically designed for high-altitude operations, where air traffic volumes are significant, and there is a need for strict separation between aircraft to maintain safety and efficiency. Because visual flight rules (VFR) operations are not permitted, this airspace is tightly controlled by air traffic control to manage the flow of IFR traffic effectively.

In contrast, Class B, Class C, and Class D airspaces allow for both IFR and VFR operations. While these classes do require ATC coordination and clearances, especially in busy terminal areas (Class B) or where air traffic is managed (Class C and D), they do not restrict operations solely to IFR flights. This distinction is crucial to understanding the regulatory framework governing aircraft operations across different categories of airspace.