Mr. Sweetie’s Simplified X-Wind Approximator

How it works:

You listen to the ASOS wind: …Wind, 250 at 16, peak gusts 24, but, as is typical, you only have Runway 18 – 36 available. What’s the crosswind component you’ll be dealing with if you try to land? Here’s a relatively easy crutch to derive a reasonably accurate crosswind component without going head down to a table that looks like a haystack or an E6B when you’re already busy enough in the cockpit.

Intuitively, a 45° crosswind should have a crosswind component of one-half the wind speed since, after all, isn’t 45° halfway around to 90°, a direct crosswind? Not so, thanks to Pythagoras, the father of trigonometry. The actual value for a 45° quartering crosswind is very close to being 75% of the reported wind speed. Trigonometric relationships aren’t linear or we wouldn’t need all those wind calculators. Here’s a mental trick that lets you approximate the magnitude of the crosswind component.

Looking at the chart above, we can see our non-linear buddy Pythagoras is already at work between 0° and 30°: 30° is only one third of the way around the arc to 90° but by 30°, the crosswind component value is 50% of the total wind speed. So we’ll use 30° as one of our checks. Only one thing matters, the angular difference between the runway heading and the wind direction. Just a tip, it’s usually easier to add than to subtract when doing math in your head.

This method checks two values, 30° and 50°, against the angular difference between the wind and the runway headings. For the example mentioned in the first paragraph, picking the lowest number, the runway heading of 180°, 180° + 30° is 210°. Not yet equal to the 250° wind so we’re definitely above our 30° ‘checkpoint’ value of 50%, or one-half.

The second step is comparing the 50° difference. 180° plus 50° is 230°. Still not equal to 250°, the reported ASOS wind direction. By this point you’ve figured out you’re dealing with a crosswind in excess of 50° to the runway, and the other ‘checkpoint’ value 75%, or three-fourths of the ASOS wind speed.

Genius that you are, you also could have calculated it directly; “If I land on one-eight, that means I have to add 70° to equal the 250° ASOS wind direction.” From the colorful illustration above that you’ve now committed to memory, 70° is inside the red arcs above the 60° threshold for “All of it”, the whole 24 knots, to apply. The only remaining question for you at that point is “Do I feel lucky?”

A second example: ASOS reports “….wind, 180 at 12, peak gusts, 16,….” The airport has only a 5 –23 runway available.

This time, 180°, the wind direction, is the lower number and you always add 30° and 50° to the lower number for quick figuring. 180° plus 30° is 210°, less than the runway heading, so you know you’ll be dealing with more than half the reported wind speed as a crosswind. 180° plus 50° is 230°, exactly the runway heading. You can conclude that you’re going to deal with a crosswind equal to three-fourths of the peak wind gust velocity. In this example, you ask yourself, “Can I handle this aircraft in a 12 knot crosswind?”

Summarizing, this method presents a practical way to quickly determine a working crosswind component without bringing your eyes inside the airplane at a critical time.

Keep the three crosswind relationships in your head, 0° to 30° = one-half the wind speed; 50° = three-fourths of the wind speed; and 60° and above, = the reported wind speed.

For us visual people, imagine a pair of segments aligned with the runway as you’re coming down final. A quick glance at the windsock and you can do some quick gozintas.* A crosswind coming from either side of the nose in the green segments less than 30°, expect a crosswind no higher than half the reported wind speed; if wind is coming from about 45°, in the orange segments, anticipate a crosswind three-quarters of the reported value, and at much more than 50°, in the red segments, expect the crosswind to equal the reported wind speed. See the diagram below.

* Gozintas. A colloquial term not found in the Airman’s Information Manual, attributed to Jethro Bodine of Beverly Hillbillies fame, referring to certain rote mathematical relationships. For example, 2 gozinta 6 three times, 10 gozinta 100 ten times, etc.