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 practical bit where we actually use the CAP 698 performance manual to calculate landing distance for a specific aeroplane. First, the golden rule before you even touch the graph: always read the associated conditions first. At the top of the graph you'll see the power and flap settings that the graph is based on. You must match those. Also, this particular graph assumes a runway that is paved, level and dry. If your actual runway conditions differ from those, you'll need to apply correction factors to the values the graph gives you — we covered those correction factors earlier in the book. Now, the graph itself is made up of four distinct "carpets" — think of them as four separate calculation stages laid out side by side. The left-hand carpet handles variations in temperature and pressure altitude. This part accounts for the effect of air density on landing distance. Hotter air or higher altitude means less dense air, which affects how the aeroplane performs. The middle carpet accounts for the effect of mass — how heavy the aeroplane is. To the right of that is the wind correction carpet. Notice the difference in slope between the headwind and tailwind lines. That slope difference is because the 150% and 50% wind rules have been applied — headwinds reduce landing distance by up to 150% of the wind component, tailwinds increase it by 50%. The last carpet on the far right is there because the landing starts at a height of 50 feet above the landing surface. If you travel straight through this last carpet, you'll only calculate the landing roll — which in the worked example on the graph is 1120 feet. Now, the best way to learn this is to follow the example that's already worked out for you on the graph itself. There's also another 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 want practice, the questions at the end of the chapter will give you plenty. Let me show you the graph so you can see the layout.