Arrival capacity at major airports is a primary constraint that must be overcome to reach the Next Generation Air Transportation System (NextGen) capacity goals. At the nation's busiest airports with closely spaced parallel runways for arrivals, capacity can be reduced significantly when weather at these airports falls below visual approach minima. When visual approaches can be used for arriving aircraft, pilots can apply their experience and judgment to position their aircraft to avoid wake turbulence generated by other aircraft they are following to the airport. This practice allows for the best arrival capacity to be achieved in good weather. When ceiling and visibility fall below that required for visual approaches, airports that would normally arrive on two parallel runways spaced less than 2500 feet (ft) apart, must discontinue parallel approaches, thus reducing the arrival rate to what can be achieved with a single runway. This reduction in capacity is due to the air traffic control (ATC) requirement that parallel runways spaced this closely must be treated as one runway for application of wake turbulence separation. A new wake turbulence procedure has recently been approved for use at several airports that allows arrivals at these airports to reduce separation between aircraft on parallel approaches in weather below visual approach minima using a parallel dependent stagger arrival operation. This procedure, documented in JO 7110.308, allows aircraft to arrive in staggered pairs, with Large and Small wake category aircraft in the lead. With this procedure, approximately half of the capacity normally lost due to deteriorating weather can be regained. Additional procedures are being explored, such as Wake Turbulence Mitigation for Arrivals (WTMA) that will allow additional gains in capacity by including additional airports with more closely spaced runways, and additional wake category aircraft participating as leaders in this parallel dependent stagger approach procedure. The MITRE Corporation's Center for Advanced Aviation System Development (CAASD) has been supporting the Federal Aviation Administration (FAA) Wake Turbulence Office to evaluate the feasibility and capacity benefit of these improvements. This paper provides an overview of the WTMA concept and describes analysis techniques used to develop initial estimates of the capacity improvement that various phases of WTMA will provide.
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