I love this image because it makes clear the confusing nomenclature of runways.
Sea-Tac is a category IIIb certified airfield, allowing operations in all but the worst conditions. There are three runways:
- Runway #1 16L/34R – 11,901 feet
- Runway #2 16C/34C – 9,426 feet
- Runway #3 16R/34L – 8,500 feet
The southern ends of the runways are labelled ’34’ Right, Center, Left (from east to west). So a plane landing on 34L is coming in from the south and landing on Runway #3.
The northern ends of the runways are labelled ’16’ Left, Center, Right (from east to west). So a plane landing on 16R is coming in from the north and landing on Runway #1.
Easy, right? 😀
Note the elevations and length of each runway. And also take note of the distance between each runway (see how the space between Runway #1 and Runway #2 is so much wider than the space between Runway #2 and Runway #3?) These are all very significant for determining the types of take offs and landings that are most suitable (more on this soon).
Going With The Flow
When people in the know are talking about flights they will mention the term ‘Flow’. This simply means the direction in which planes are arriving and departing.
- North Flow means the planes are arriving at the south end runways (34R, 34C, 34L) and taking off from the north end heading northward.
- South Flow means the planes are arriving at the north end runways (16R, 16C, 16L) and taking off from the south end (34R, 34C, 34L) south end heading south.
Flight operations, both take offs and landings, all move in one direction at a time. At Sea-Tac this means either North Flow or South Flow.
In general planes will take off by flying into the prevailing wind direction. So if the wind is coming from the north, the airport will use North Flow. And if the wind is coming from the south, the airport will use South Flow.
When the wind changes, the airport will go through a process where they switch Flow. This doesn’t happen all that often because the wind doesn’t shift dramatically all that often. In fact, changing Flow is occurring less and less as traffic increases, partly because modern jet engines are so powerful that the wind direction no longer has much an impact on the safety and efficiency of the flight. Another way to put it is that the cost and hassle of switching Flow often doesn’t pencil out when the airport is very busy.