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I know that there are three type of wind, headwind, tailwind and crosswind. What degree of wind direction can distinguish it? 30 or 45 degree?

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    $\begingroup$ So you want to know how many degrees of crosswind component qualifies a wind to officially be called a "crosswind"? You won't find that any where in the FARs or AIM, so I guess it's not a real thing. $\endgroup$ – quiet flyer Aug 30 '20 at 13:26
  • $\begingroup$ I'm not sure we can speak in degrees. I think we usually divide the wind in 2 components (one on the axis of whatever you consider --route, runway,...-- and another perpendicular) and speak of cross-wind component. crosswind would be if the sideway component is above a threshold. $\endgroup$ – Manu H Aug 30 '20 at 13:51
  • $\begingroup$ Ah I just thought of the real answer-- if there's enough sideways wind component that we should land with a sideslip rather than a forward slip, then it counts as a crosswind. $\endgroup$ – quiet flyer Aug 30 '20 at 16:00
  • $\begingroup$ We should probably look at wind as only having two types, crosswind and wind in our direction of travel. Headwind and tailwind are the same type. One is the inverse of the other. Or, you can say that one is the negative and one is the positive of the same type. Otherwise, why wouldn’t you say that there are four types of wind: headwind, tailwind, left crosswind, and right crosswind? And, breaking it down further into quartering winds would confuse matters even more by adding four more types. It is more correct to say that there is only one type broken into two components for our practical use. $\endgroup$ – Dean F. Aug 30 '20 at 16:54
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Manu H has given what, to me, sounds like as close to a textbook answer as you can get.

Crosswind is always 90° to your direction of travel. You base crosswind off of your track instead of your heading. Regardless of your track or heading, or the wind direction, the crosswind intensity would be a percentage of the total wind intensity ranging from 0% to 100% coming from 90° to your direction of travel. You can find the numeric value of the crosswind using Pythagorean’s Theorem. The headwind/tailwind component and the crosswind component make up two of the legs of the mathematical 90° triangle. The actual wind bearing from your direction of travel and its intensity make up the hypotenuse.

Or, you can use the graph, below: enter image description here

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    $\begingroup$ FYI, a good rule of thumb (that you can see in the graph) is to treat any crosswind above 60° as the same as 90° and for less than 60° use a “clock" estimate. e.g 15° is 1/4 of an hour so the crosswind is 1/4 of the wind velocity. 30° is 1/2 of an hour so the crosswind is 50% of the wind velocity. $\endgroup$ – JScarry Aug 30 '20 at 17:14
  • $\begingroup$ @JScarry Never heard that technique before, but that is tremendously cool. Pity I can't award a bounty to a comment - that one would qualify! $\endgroup$ – Ralph J Aug 30 '20 at 19:31
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Any wind that is not perfectly parallel to the runway is a crosswind, because any non-parallel wind has always a 90º component, big or small...

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