Final answer:
The airspace where operational need exists for controlled airspace not fitting Class A, B, C, or D is Class E. It is used for en route segments of IFR operations and managing VFR flights where necessary, contributing to air traffic safety and efficiency.
Step-by-step explanation:
The airspace designated where an operational need exists for controlled airspace but does not meet the requirements for Class A, B, C, or D is typically referred to as Class E airspace. Class E airspace is controlled airspace that extends upward from either the surface, 700 feet above the surface, or 1,200 feet above the surface, depending on the area. It is utilized for en route segments of instrument flight rules (IFR) operations and for when control of VFR aircraft is necessary.
Classes of airspace are part of a broader regulatory framework designed to ensure the safety and efficiency of air traffic. Class E airspace, being controlled, means that air traffic control (ATC) may not necessarily give clearance for VFR flights, but IFR flights will be under the guidance of ATC within this airspace. It's essential in areas where a significant volume of IFR operations or a mix of IFR and VFR operations occur.