Single-engine Class B - Climb — Page 308, Lesson 388

We're starting a new topic now: the climb performance for a single-engine Class B aeroplane, and specifically how we use the climb graph data. Let me walk you through it. There are two main uses of the climb graph. The first is to calculate the time to climb to the cruise altitude. For that, the pilot needs to know two things: the cruise altitude and the rate of climb. So you read the graph, you get your rate of climb, and you work out how long it takes to get up there. The second use is where things get a bit more careful. If you're using the gradient from this graph to calculate obstacle clearance or ground distance, then you must adjust that gradient for the effect of wind. This particular climb graph makes no correction for wind — it's a clean, still-air graph. And here's the reason: obstacle clearance calculations and ground distance calculations use ground gradients. A ground gradient is a gradient measured relative to the ground, and ground gradients are affected by wind. So if you don't correct for wind, your obstacle clearance and ground distance numbers will be wrong. Now, if you need to refresh your memory on the difference between ground gradients and air gradients and how wind affects them, go back to the general performance principles climb chapter — that's where we covered that distinction. Let me also point you to the examples in CAP 698, which is the CAA performance manual. There are example calculations there for you to work through and practise. On page 6 of section 2, there's an example on how to calculate the climb gradient using the graph. Just below that, there's another example to determine the maximum permissible mass in order to achieve a 4% climb gradient. That maximum permissible mass is sometimes referred to as the MAT or WAT limit — MAT stands for maximum allowable take-off mass, and WAT stands for weight, altitude, temperature. So that's the mass limit driven by the climb requirement. Then on page 8 of section 2, there's another example: how to calculate the horizontal ground distance required to climb to a given height. And that brings us to the questions. These are the book's practice questions — let's try them one at a time.