takeoff. The direction of wind at a runway is measured using a windsock and the speed by an anemometer, often mounted on the same post. Headwind and Tailwind are opposite interpretations of the wind component which is parallel to the direction of travel, while Crosswind represents the perpendicular component. Determining the ground speed of an aircraft requires the calculation of the head or tailwind. Assume: Then For example, if the wind is at 09015 that means the wind is currently from heading 090 degrees with a speed of 15 knots and the aircraft is taking-off from runway 24; having heading of 240. The pilot prefers the runway side with less than 90 difference from wind direction, in this case Runway 06; heading 060. Here, . The aircraft is said to have 7.5 knots of crosswind and 13 knots of headwind on runway 06, or 13 knots of tailwind on runway 24. Aircraft usually have maximum tailwind and crosswind components which they cannot exceed. If the wind is at eighty degrees or above it is said to be full-cross. If the wind exceeds 100 degrees it is common practice to takeoff and land from the opposite end of the runway, it has a heading of 060 in the above-mentioned example. See also Crosswind Air navigation Thrust Wind assistance Windsock References Aerodynamics