When used concerning wind conditions the word means the component of wind that blows 90 degrees to the direction of the runway. Generally crosswinds make landings more difficult than if the wind were blowing parallel to the direction of the runway. When crosswinds are strong enough, they may exceed an aircraft's designed crosswind limit, and attempting to land under such conditions could cause structural damage to the aircraft and is potentially dangerous.
To calculate a crosswind (known as a crosswind component), pilots usually refer to a crosswind component diagram designed specifically for the aircraft they are flying. These diagrams can often be found in the pilot’s operating handbook (POH) and/or aircraft reference manual. In addition, crosswinds can also be computed by multiplying the wind speed by the sine of the angle between the wind and the direction of travel.
To counteract crosswinds, pilots often perform a crosswind landing to land the aircraft safely in dangerous crosswind conditions. A crosswind landing is a landing maneuver in which a significant component of the prevailing wind is perpendicular to the runway centerline. The three most popular and widely utilized crosswind techniques that are used to correct for cross winds are: De-Crab, Crab, and Sideslip.