An aspect of airport terminal operations that holds potential for efficiency improvements is the separation criteria applied to aircraft for wake vortex avoidance. These criteria were made to represent safe spacing under weather conditions linked to the longest wake hazards, and are consequently overly conservative during a significant portion of operations. Under many ambient conditions, such as moderate crosswinds or turbulence, wake hazard durations are substantially reduced. To realize this reduction both USA and Europe have developed "proof-of-concepts" aircraft wake vortex spacing systems. System prototypes were successfully operated in real-time already back in 2000. The systems are typically an integration of weather sensors, wake sensors, and numerical algorithms for wake transport and decay predictions. Gains in airport throughput using prototype spacing systems as compared to the current criteria averaged to 6%, with peak values approaching the theoretical maximum of 16%. The average throughput gain translates to 15-40% reductions in delay when applied to realistic capacity ratios at major airports.