Class A - Additional Take-off Procedures — Page 421, Lesson 516

We're moving into the final piece of the Class A additional take-off procedures. We've already worked through the wet runway and contaminated runway mass and speed adjustments, so now I want to finish that sequence and then introduce the third procedure, which is the most common one you'll actually use in the line. Let me close out the first procedure first. After you've worked through the climb limit graph, you repeat the entire process in the improved climb performance tyre speed limit graph, which is CAP 698 Figure 4.16. The only difference is the initial entry point: instead of entering with the climb limit mass, you enter with the tyre limit mass minus the climb limit mass. So you're finding how much extra mass the tyre speed limit will allow you to carry, on top of what the climb limit already gave you. Now, you'll end up with two mass increases — one from the climb limit graph and one from the tyre speed limit graph. The rule is simple: you take the lower of the two mass increases, and you use that one together with its associated speed increases. You then add that mass increase to the normal climb mass limit. Once you have that increased mass, you determine the V speeds for it, apply the speed increases to the appropriate speeds, and finally check VMBE — that's the maximum brake energy speed, the speed beyond which the brakes cannot absorb the energy of a rejected take-off. That check is your final safeguard. Now, the third additional procedure — and this is the one you'll see most often in everyday operations. It goes by many names: reduced thrust take-off, variable thrust take-off, or assumed temperature take-off. Airbus calls it the flexible take-off. All of these refer to the same thing. The main reasons for doing it are to preserve engine life and to help reduce noise. You can use it any time the actual take-off mass is less than the maximum permissible take-off mass, and there is an available distance that greatly exceeds what is required. The maximum reduction in thrust from the full rated take-off thrust value is 25%. So you can never cut the thrust by more than a quarter of the full rated value. Now, there are strict prohibitions. Reduced thrust take-off is not permitted with icy or very slippery runways, contaminated runways, anti-skid inoperative, reverse thrust inoperative, an increased V2 procedure, or PMC off — that's the power management control, the system that automatically sets and maintains the engine thrust. And it's not recommended if potential windshear conditions exist. The principle behind it is elegant. The procedure essentially assumes that the temperature is a lot hotter than it actually is. Imagine the outside air temperature continually increasing — as it does, the thrust produced by the engines continually decreases. There will eventually be a temperature beyond which there is insufficient thrust to complete a take-off. That temperature is then used as the assumed temperature, and the thrust equating to that temperature is set as the take-off thrust. So you're deliberately setting less thrust than the engines could give you, because you don't need full thrust for this particular take-off — and that saves engine wear and reduces noise. The full procedure is detailed on page 31 of section 4 in CAP 698, so you don't need to memorise every step — you'll use that page as your reference. But the core concept is this: you're trading excess performance for engine preservation, within a strict 25% limit and with clear prohibitions on runway and system conditions.