FSX uses a 'scoring' system to determine runway assignment, but in the end the primary factors are:
Wind direction (over 16 knts I believe) determines runway(s) in use.
If parallel are in use........
For arrivals-direction from which aircraft is arriving, i.e. (KSEA) from the east, 16L/34R; from the west , 16R/34L.
For departures-runway nearest the parking spot that meets minimums for the aircraft.
For KSEA downloads here at SimV:
http://simviation.com/1/search?submit=1&keywords=ksea&categoryId=54. The 3rd one, KSEA.zip, adds the 3rd runway and taxiways to default scenery. For others, look here:
http://www.freewarescenery.com/fsx/us.htmlAirport downloads should work fine WOAI. They generally will not change runway usage....
(Added-[timestamp=1357833378])...though there are 'tricks' that designers can use, most often with parellel runways. KSEA.zip, that I mentioned above, has takeoffs limited to 16L/34R with landings on the other 2 parellel runways. This does help congestion during busy times.
At that time [1909] the chief engineer was almost always the chief test pilot as well. That had the fortunate result of eliminating poor engineering early in aviation.
