What type of airspace requires a different separation standard for IFR flights compared to non-IFR flights?

In Class A airspace, the separation standards for IFR (Instrument Flight Rules) flights are distinctive compared to those for non-IFR flights. Specifically, Class A airspace extends from 18,000 feet MSL (Mean Sea Level) up to and including FL 600 (60,000 feet) and is entirely designated for IFR operations. This airspace requires all aircraft operating within it to be under positive control from air traffic control.

The separation standards in Class A airspace are more stringent because it involves high-altitude operations where the volume of traffic is significant, and the risk of collision is much higher. IFR flights are separated from each other by specific vertical and horizontal distances that do not apply to non-IFR flights operating outside of this airspace structure.

In contrast, the other classes of airspace (B, C, and D) have different operational requirements and may accommodate both IFR and visual flight rules (VFR) traffic without the same level of separation standards that are inherent to Class A. Thus, Class A uniquely requires this different standard for IFR flights.