Let me start with the big picture — Page 426, Lesson 526

I want to walk you through the take-off climb segments for a Class A aeroplane. This is the heart of how we define the climb path after the wheels leave the ground, and it's broken into four distinct segments, each with its own configuration, speed, and gradient requirement. Let me start with the big picture. The take-off flight path begins once the take-off is complete — that means at 35 feet above the runway, with the aeroplane at V2, and one engine deemed inoperative. That 35-foot height is called the screen, and it marks the start point of segment 1. Now, the gradient requirements you'll see in Figure 16.1 are expressed as percentages, and they depend on how many engines you have operating. For four engines, the minimum gradient is greater than zero percent. For three engines, it's greater than 0.3 percent. And for two engines, it's greater than 0.5 percent. These are the absolute minimums for the first segment. Let me define what gradient means here. It's the ratio of vertical climb to horizontal distance, expressed as a percentage. A positive gradient means you're actually climbing, not just holding altitude. Now, segment 1. The objective at this point is to climb as expeditiously as possible. That's difficult because of the lack of excess thrust — you have a large amount of drag created by the landing gear and the flaps, and you've lost one engine. So the strategy is to retract the gear and flaps as soon as possible. But here's the catch: retracting flaps at low speeds close to the ground is dangerous. So the only option is to retract the gear. Once the gear is up and locked, the first segment is finished. During this segment, the steady gradient of climb must be positive — that's your minimum. Segment 2 starts at the end of segment 1, which is when the gear is up. The objective now is to retract the flaps. However, flap retraction is not permitted below 400 feet. So the pilot's action is simply to climb, at no less than V2, until 400 feet is reached. Once 400 feet is reached and flap retraction can commence, segment 2 ends. Now, since the main source of drag — the gear — has been removed, the minimum gradient requirement becomes more severe. It's no less than 2.4 percent for four engines, 2.7 percent for three engines, and 3.0 percent for two engines. Segment 3 starts at or above 400 feet, and this is the flap retraction and acceleration segment. Here's the key issue: retracting the flaps will increase the stall speed. That reduces the aeroplane's safety margin. So the aeroplane must accelerate during flap retraction from V2 to the zero flap speed, and then to the final take-off speed. The final take-off speed is also called the final segment speed, and it's intended to be the one-engine-inoperative best angle of climb speed. Once this acceleration is complete, thrust can be reduced from maximum take-off thrust — that's TOGA — to maximum continuous thrust, which is MCT. Now, there's a critical time limit here. Maximum take-off thrust is limited to only 10 minutes. So acceleration and flap retraction must be complete by then. In this segment, our priority is to accelerate, not to climb. We require excess thrust to enable us to climb or accelerate, and since our priority is acceleration, there is no minimum climb gradient required for segment 3. The only way we can quantify this acceleration requirement is through the speed increase itself. Let me pause and make sure you have the speed relationships clear. V2 is the take-off safety speed — the speed at which you climb with one engine out. VZF is the zero flap speed. VFTO is the final take-off speed, also called the final segment speed. And MCT is maximum continuous thrust, the power setting you use after the 10-minute TOGA limit expires. Segment 4, which is the final segment, continues the climb from above 400 feet up to 1500 feet AGL — that's above ground level. The configuration is flaps up, speed is VFTO, and thrust is MCT. The gradient requirement here is at least 1.2 percent for four engines, 1.5 percent for three engines, and 1.7 percent for two engines. This segment ends at 1500 feet AGL, which completes the take-off climb path. Let me give you the reference points again so you can see the whole picture. Segment 1: from 35 feet to gear up, at V2, with positive gradient. Segment 2: from gear up to 400 feet, still at V2, with the 2.4/2.7/3.0 percent gradient. Segment 3: from 400 feet, flap retraction and acceleration from V2 to VFTO, no minimum gradient, and thrust reduced from TOGA to MCT. Segment 4: from above 400 feet to 1500 feet AGL, at VFTO with MCT, with the 1.2/1.5/1.7 percent gradient. One thing I want to emphasize: the 10-minute TOGA limit is a hard constraint. It's why the acceleration and flap retraction in segment 3 must be completed within that time. If you don't, you'd be exceeding the certified limit for maximum take-off thrust, which is not acceptable in professional operations. Now, let me show you the visual layout of these segments so you can see how they stack up vertically.