The air traffic direction, North Flow or South Flow, is primarily based on airfield and enroute wind and weather conditions.  As a safety factor, aircraft arrive and depart into the wind to maximize aerodynamic lift.

Typical North Flow Operations (Figure 1)*:

Click to see a regional depiction of Dulles International operations in North Flow (PDF file)

Typical South Flow Operations (Figure 2)*:

Click to see a regional depiction of Dulles International operations in South Flow (PDF file)

*  FAA Procedures for Dulles International (IAD):

• Search by Airport Identification:  IAD
• https://www.faa.gov/air_traffic/flight_info/aeronav/procedures/