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traffic pattern[′traf·ik ‚pad·ərn]
The traffic flow that is prescribed for aircraft landing at, taxiing on, and taking off from an airport; the usual components of a traffic pattern are upwind leg, crosswind leg, downwind leg, base leg, and final approach.
The regulated movement of air traffic that must fly along an established route when approaching or leaving an airport. Airplanes fly very precise rectangular patterns around an airport prior to landing. Each side of the rectangle has a name. The leg flown at right angles to the runway immediately after takeoff is the crosswind leg. The leg flown parallel to the runway and opposite to the direction of landing is the downwind leg. The base leg, as it is known, is flown at right angles to the runway, just before turning to the final direction for landing. Flight in the direction of landing but maintaining altitude is called an upwind leg. Traffic patterns may be flown with either right-hand or left-hand turns.