How many aircraft sustain continuous airborne coverage?

How many aircraft are needed to maintain continuous airborne coverage?

Four can keep one airborne and one on alert, six can maintain two airborne, and eight provide more margin. The later clarification specifies four helicopters for AEW.

Four aircraft can keep one airborne and another on alert. Six can sustain two aircraft in the air, while eight provide a stronger margin. Maintaining continuous coverage therefore takes more airframes than the number flying at any one time. Four helicopters are subsequently specified for airborne early warning.