Right, let's pick this up — Page 336, Lesson 412

Right, let's pick this up. We're looking at the landing distance graph, and I want you to pay particular attention to the power and flap settings shown at the top of the graph. Those are your starting conditions — the graph is built for a specific configuration, and you must match it. Now, a critical assumption baked into this graph: it assumes a runway that is paved, level, and dry. If your actual runway conditions differ from those specified — say it's wet, or it's a grass strip, or it's sloping — then the values this graph gives you will not be valid. You'll need to apply corrections to those values, and we covered those correction factors earlier in the book. Let me walk you through the anatomy of the graph, because it's built as a series of "carpets" — each one handles a different variable. 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, warmer air and higher altitude mean less dense air, which affects how the aeroplane performs. The middle carpet accounts for the effect of mass. To the right of that is the wind correction carpet. Now, notice the difference in the slope of the headwind and tailwind lines. That's not random — it reflects the 150% and 50% wind rules that have been applied. Headwind and tailwind don't affect landing distance symmetrically, and the graph encodes that. The last carpet, on the far right, is labelled "obstacle height." Now, there's no physical obstacle as such, but you'll recall that the landing distance is measured from a height of 50 feet above the landing surface. That's your reference point — the landing starts at 50 feet. Now, the best way to get comfortable with this graph is to follow through the worked example that's carried out on the graph itself. That will show you the correct sequence of entering the graph. And there's another example at the bottom of page 9 of section 2 in CAP 698 that you can work through as well. Use those examples — they're there to help you. And if you want practice working through the graphs, the questions at the end of the chapter will give you that.