Let's pick this up right where the wind component plotting gets interesting — Page 182, Lesson 162

Let's pick this up right where the wind component plotting gets interesting. We've already drawn the crosswind limit lines, and now we're adding a second constraint: a minimum headwind. Here's the scenario. You have a minimum headwind of 10 knots and a crosswind limit of 20 knots. So, on your wind slide, you draw in the 20-knot crosswind parallel markers, just like before. But this time, you also draw in a 10-knot headwind limit line. That's the new element. Now, you rotate the slide to the direction the wind is coming from. In this example, that's 030° magnetic. Look at where your two lines intersect the centre line. The crosswind lines intersect at 11 knots, and the headwind line intersects at 31 knots. Those two intersection points define your acceptable wind window. Let me explain what those numbers mean. If the wind from 030° magnetic is less than 11 knots, you have less than 10 knots of headwind down the runway. That means you cannot land. If the wind is greater than 31 knots from 030° magnetic, you have more than 20 knots of crosswind component. Again, you cannot land. But if the wind is between 11 and 31 knots from 030° magnetic, you have 10 knots or more of headwind component, AND you have 25 knots or less of crosswind component. That's your acceptable window — you can land. Now, let's talk about tailwind components. In general, you should avoid landing with a tailwind. If you're given a runway with a tailwind component, ask ATC if you can use the other end. It's usually poor airmanship to accept a tailwind, and you won't have a leg to stand on afterwards if you run off the end — even if your brakes fail. However, you may occasionally have questions that involve tailwind components, so you should know how to deal with them. The first thing to notice is that you cannot directly plot the horizontal line representing a tailwind component in the normal way, because it's above the horizontal scale line. You're in the curved part of the wind slide. Let's take a worked example. Your runway is 09, variation is 10 degrees east, and the ATIS wind is 320/10G30. Your maximum tailwind component for this particular landing is 10 knots. The question is: what is the maximum wind speed from the given direction that you can accept? First, note that the ATIS wind is magnetic direction, so the value of variation is unnecessary information. Ignore it. Watch out for that trap. Bring the runway direction, 09, round to the top. Now move the speed slide to bring 10 knots under the centre dot. Draw in the tailwind component limit line. Then, and this is critical, do not forget to move the speed slide back to put zero under the centre dot. That's the key step — you must reset the slide before you read off your answer. The tailwind limit line is drawn in the curved part of the slide, above the horizontal scale line, so you have to handle it differently from the headwind and crosswind lines we did earlier.