ATPL · Navigation · Mass And Balance And Performance Atpl Ground… lesson — Page 308, Lesson 387

Let me walk you through this. We've just been talking about why there's no operational regulation on climb performance for this class of aeroplane. The reason is that the certification specifications for this type of aeroplane, as stated in CS-23, are stringent enough on their own. CS-23 is the certification standard that the aeroplane type had to meet to be certified in the first place. So the regulator decided that the climb performance requirements baked into the certification are already strict enough that they don't need a separate operational rule on top of it. But here's the important point. Even though there's no operational requirement for a minimum climb performance, it would not be safe to operate the aeroplane in such a manner that its performance is so poor it's barely able to climb. So as a pilot operating this class and type of aeroplane, it's your job to know what climb performance would be achieved, so that the aeroplane will at least be able to climb sufficiently. The certification guarantees a baseline, but you still have to manage the operation so you don't degrade that performance to a dangerous level. Now let's look at how the data is presented. Provided in most pilot operating manuals or aeroplane flight manuals are climb graphs that help the pilot to calculate the gradient of climb. The gradient of climb is the ratio of height gained to horizontal distance travelled — essentially how steeply the aeroplane climbs. Such a graph can be found in CAP 698, in section 2, page 7, figure 2.3. CAP 698 is the Civil Aviation Publication that contains the performance data for these aeroplanes. As with any graphs, before you use it, you must ensure you are familiar with the associated conditions of that graph. Every performance graph is only valid under specific conditions, and if you don't meet those conditions, the numbers you read off will be wrong. In this particular graph, the throttles are at maximum, the mixture is rich, the flaps and gear are up, and the cowl flaps are set as required. So this graph assumes full power, a rich mixture for cooling and power, a clean configuration with flaps and gear retracted, and cowl flaps positioned according to the manual. The climb speed for the graph is taken to be 100 knots indicated airspeed for all masses. So regardless of how heavy the aeroplane is, the graph assumes you're climbing at 100 knots indicated. That's a fixed reference speed for this graph. The graph has an example that you can follow using the dashed black lines, so you can practise on your own. Graph accuracy is very important, so try to be as careful as possible when using them. Be especially careful when working out your true airspeed, which is needed when you approach the right-hand side of the graph. You may need your navigation computer to do this, because the true airspeed might not be given to you — such as is the case in the example. So on the right-hand side of the graph, you'll need to convert from indicated airspeed to true airspeed, and that conversion accounts for altitude and temperature, which is why you need the navigation computer. Let me show you what this looks like. So to summarise what I want you to take away. The certification under CS-23 is what guarantees a minimum climb standard, but it's your responsibility as the pilot to know the actual climb performance you'll achieve. You get that from the climb graphs in the manual, and you must always check the conditions the graph assumes — maximum throttle, rich mixture, flaps and gear up, cowl flaps as required, and 100 knots indicated. And when you use the graph, be precise, especially when you need true airspeed on the right-hand side, which may require your navigation computer.