Right, let's get into the landing distance graph — Page 368, Lesson 448

Right, let's get into the landing distance graph. This is the tool we use to calculate the landing distance for a specific aeroplane, and it's the graph that ties together all the factors that affect the aeroplane's performance on landing. First, the golden rule: before you even start tracing lines on the graph, always look at the associated conditions at the top. Pay particular attention to the power and flap settings. These are the configuration the aeroplane is in for the landing, and the graph is only valid for that specific setup. If you're using a different power or flap setting, this graph doesn't apply. Also notice the runway assumption. This graph assumes the runway is paved, level, and dry. That's the baseline. If your actual runway conditions are different—say it's wet, or it's a grass strip, or it has a slope—then the values the graph gives you will need corrections. We covered those correction factors earlier, so you'll apply them after you get your raw distance from the graph. Now, let's look at the structure of the graph itself. It's divided into four "carpets," or sections. The left-hand carpet deals with variations in temperature and pressure altitude. This part accounts for the effect of air density on landing distance. Remember, hot air and high altitude mean less dense air, which means the aeroplane needs more distance to land. That's what this carpet is correcting for. The middle carpet accounts for the effect of mass. Heavier aeroplane, longer landing distance. Simple as that. To the right of the mass carpet is the wind correction carpet. And here's a key detail: notice the difference in the slope of the headwind and tailwind lines. They're not parallel. That's because the 150% and 50% wind rules have been applied. A headwind reduces landing distance, and a tailwind increases it, but not symmetrically—hence the different slopes. Finally, the last carpet on the far right. This one exists because the landing distance is measured from a height of 50 feet above the landing surface. That's the standard reference height. If you travel straight through this last carpet, you'll only calculate the landing roll—the distance from touchdown to stop. In the example on the graph, that landing roll is 1120 feet. Now, the best way to learn this graph is to follow the example that's already worked out for you on the graph itself. Trace the lines, see how each carpet feeds into the next. There's also another worked example at the bottom of page 20 of section 3 in CAP 698 that you can work through. Use those examples—they're there to help you. And if you need more practice, the questions at the end of the chapter will give you plenty of reps. So, to sum up: check the conditions first, understand the four carpets—density, mass, wind, and the 50-foot height—and then follow the example to see how it all comes together.