What does Class E airspace require for IFR traffic?

In Class E airspace, IFR (Instrument Flight Rules) traffic is required to obtain an ATC clearance before entering that airspace. This requirement is essential for maintaining a high level of safety and efficiency in the airspace system, ensuring that air traffic controllers can manage and coordinate the movements of IFR flights effectively, especially in areas where visibility may be limited, such as during poor weather conditions.

While other options hint at the operational protocols of Class E airspace, none capture the essential need for an ATC clearance for IFR operations. The clearance ensures that IFR flights are properly separated from each other and from VFR traffic (Visual Flight Rules flights), which may be operating under different flight rules and altitudes. This requirement is part of the overall safety protocols in the national airspace system, allowing for systemic order and the safe passage of various types of aircraft.