Class A Aircraft - Take-off — Page 395, Lesson 493

We’re now inside the actual take-off speed tables from CAP 698, Section 4. I want to walk you through how we read them, because this is where the regulated take-off mass gets turned into the actual V speeds we’ll use. First, the structure. There are two sets of speed tables. One is for a 5-degree flap setting, and the other is for a 15-degree flap setting. In our example we’re assuming 5 degrees of flap, with a regulated take-off mass of 57,900 kg. So we go to the 5-degree table. Now, the table is organised by speed bands. We identify the column for speed band B — that’s roughly in the middle of the page. The left-hand scale of the speed table is mass. Our regulated take-off mass of 57,900 kg lies between the 55,000 kg and 60,000 kg marks on that scale. Because our mass isn’t exactly on a printed line, we have to interpolate. Let me show you the interpolation for V1. For 55,000 kg, V1 is 138 knots. For 60,000 kg, V1 is 145 knots. Correct interpolation for 57,900 kg gives V1 equal to 142.06 knots. We’ll round that shortly — I’ll come back to the rounding. Now we do the same exercise for VR and V2. For 57,900 kg, VR comes out to 145 knots, and V2 comes out to 152 knots. But here’s the critical part — V1 is not final yet. V1 must be corrected for slope and wind, using the table at the top of page 18. That correction table is reproduced for you in Figure 14.18. So the speed table gives you the base V1, and then you apply the slope and wind correction on top of it before you round. Let me make sure the picture is complete. We have three V speeds here: V1, VR, and V2. V1 is the decision speed — the speed up to which you can still abort the take-off and stop safely on the remaining runway. VR is the rotation speed — the speed at which you begin to rotate the aircraft to lift off. V2 is the take-off safety speed — the speed you must reach by 35 feet above the runway, and it’s the minimum safe climb speed with one engine inoperative. Those are the definitions that make these numbers meaningful. So the sequence is: take your regulated take-off mass, go to the correct flap table, pick the speed band column, interpolate between the mass marks to get V1, VR, and V2, then correct V1 for slope and wind using the correction table at the top of the page. Only after that correction do you round the final V1. One thing I want to stress — the interpolation is not optional. If your mass falls between two printed values, you must interpolate to get the correct speed. And the slope and wind correction applies only to V1, not to VR or V2. That’s a distinction worth remembering. Now, let’s look at the two figures. Figure 14.16 shows the density band selection for the take-off V speeds — that’s how you choose which speed band column to use in the first place. Figure 14.17 reproduces the speed table itself, with the areas to concentrate on highlighted in red. And Figure 14.18 shows the slope and wind correction table. So to summarise the whole process in one flow: select the flap setting, select the speed band from the density, read the mass scale, interpolate for your regulated take-off mass to get V1, VR, and V2, then apply the slope and wind correction to V1, and finally round. That gives you your take-off V speeds for the day.