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separation of the runway centerlines. Runways that converge or intersect have lower capacities because of operational interference which is inherent with this type of wnflguration. Taxiways increase capacity because they reduce the time aircraft need to be on the runway and improve access to various landside facilities. Two of the reliever system airports, Airlake and South St. Paul, have single rumvay/taxiway configurations. Anoka County-Blaine and Lake Elmo have primary and crosswind runway cenflgurations. At Anoka County-Blaine, the primary and crosswind runways bisect each other; at Lake Elmo, the runways intersect. Both configurations have essentially the same ability to process aircraft because an operation on the primary rumvay precludes an operation on the crosswind until the primary runway is clear. Crystal Airport has dual parallel runways and Flying Cloud Auport has parallel runways with a bisecting crosswind runway. St. Paul Downtown has athree-runway; A- shaped configuration. The parallel runway configuration at Crystal and Flying Cloud airports provides the most efficient operational configuration, because aircraft can be staged to approach and/or depart from either airport with greater frequenry. Separation distances between the parallel rumvays at these two airports, however, are not great enough to allow simultaneous arrivals or departures during instrument flight rule (IFR) rnnditions. Current FAA standards dictate a 4,300-foot spacing between the centerlines of parallel runways before they can accommodate simultaneous IFR activity. 2 Fleet Mix The aircraft fleet mix is also an important factor in determining airport capacity. For capacity purposes, aircraft differ by approach speed and size. Capacity decreases as the diversity of approach speeds in the operational fleet mix increases. This is because aircraft following each other, either on takeoff or departure, are spaced according to their difference in airspeeds. Heavy aircraft create wake vortices that require greater spacing between large and small aircraft. Wake vortices are typically not a factor at general aviation airports with homogeneous fleet mixes. The greater the difference in fleet size and speed, the greater the space required between aircraft, and therefore the lower the capacity. A single runway can process more demand if the operating fleet is fairly homogeneous in nature. The mix index for each reliever airport was estimated based on the projected general aviation operating fleet mix. For planning putposes, it was assumed that all single-engine and multiengine piston aircraft weigh less than 12,500 pounds (Class A and B aircraft) and all turboprop and turbojet aircraft weigh between 12,500 and 300,000 pounds (Class C aircraft). Currently, Airlake and Lake Elmo do not have turboprop or turbojet operations. South St Paul, Anoka County-Blaine, and Crystal have less than 1 percent turboprop III-3