Single-engine Class B - Landing — Page 336, Lesson 411

Right, let's pick this up with the landing despatch rule for a single-engine Class B aeroplane. This is where we turn the regulatory wording into something you can actually use in the flight planning office. The way to simplify the despatch rule is to always consider two masses. First, the greatest mass in still air. Second, the greatest mass in the forecast wind conditions. Of those two, you take the lesser mass as your despatch mass. So you're not trying to blend them or average them — you compare the two and pick the smaller one. That's your despatch mass, the number you plan around. Now, in our example, it's the still air mass that usually turns out to be the lesser one. But there's an exception, and I want you to remember this clearly. The exception is when there is a tailwind on a unidirectional runway. Let me define that term for you, because it's precise. A unidirectional runway is a runway whose direction for take-off and landing is fixed in one direction. So you can only ever operate in that one direction — no reciprocal. And in that case, the maximum landing mass in the tailwind will be less than the maximum landing mass in still air. So the tailwind case becomes the governing, the lesser, mass. Now let's move to the speed that underpins all of this — the Reference Landing Speed, VREF. You may recall that the regulatory speed at the landing screen height is called VREF. For a single-engine Class B aeroplane, it had to be no less than 1.3 times the stall speed in the landing configuration. That's written as 1.3VS0. So VS0 is the stall speed in the landing configuration, and VREF is 1.3 times that value, at the very least. A pilot must adhere to the VREF speeds. Why? Because they are the speeds which have been used to construct the landing graphs or table in the aeroplane flight manual. The performance data is built around flying at exactly that speed. If a pilot were to deviate from these speeds, the required aircraft performance would not be achieved. So VREF isn't just a suggestion — it's the speed the certified performance is tied to. Now, how do we actually calculate the landing distance? This part of the chapter deals with that. All aeroplanes will have either a pilot operating handbook or an aeroplane flight manual. The purpose of these manuals is not only to show how to operate the aeroplane but also to detail the aeroplane's performance. So the manual is your source of truth for the landing distance. The example graph we will use is figure 2.4 on page 10 of section 2 in CAP 698. That's the Civil Aviation Publication that contains the performance data. Now, a key habit: always take a look at the associated conditions first, paying particular attention to the power and flap settings as shown at the top of the graph. Those conditions define the configuration the graph is valid for. Also notice that this graph assumes a runway which — well, that's where the excerpt cuts off, but the point is the runway assumption is part of the conditions you must check before you read any distance off the graph. So to tie it together: you compare still air mass against forecast wind mass, take the lesser as despatch mass, remembering the unidirectional runway tailwind exception. You fly VREF, which is at least 1.3VS0, because the performance data is built on it. And when you go to calculate the landing distance, you use the manual's graph, but only after you've checked the power and flap settings and the runway assumptions at the top.