Now, Segment 4 — Page 426, Lesson 528

We’re in the middle of the take-off flight path segments, and I’ve just walked you through the first three. Now I want to pick up with the end of Segment 3 and then take you through Segment 4, because this is where the climb gradient requirements really come together. So, to finish Segment 3: this is the segment where the aeroplane is accelerating, and here’s the key point — there is no minimum climb gradient required during this acceleration. The only way we can quantify that acceleration requirement is by stating that the excess thrust available would be equivalent to a minimum climb gradient of 1.2%. So even though the book doesn’t demand an actual gradient here, we express the acceleration capability in those terms — 1.2% is the yardstick. Now, Segment 4. This is the final segment of the take-off flight path. It starts when three things happen together: the flaps are retracted, the final segment speed is achieved, and the thrust is set to maximum continuous thrust. From that point, the aeroplane is climbed to above 1500 ft, and that’s where the take-off flight path ends. Once you’re above 1500 ft, the pilot will either recover to the airfield or continue to the take-off alternate. And the climb gradient for this last stage must not be less than 1.2% — same figure as before, but now it’s a hard requirement, not just an equivalence. Now, I want to bring in the Class A aeroplane requirement for more than two engines. The gradient requirements for Class A aeroplanes with more than two engines form part of the syllabus, so you need to remember them. We touched on this in the previous chapter, but let me restate the concept: the climb limit mass tells us what the maximum mass of the aeroplane can be in order to achieve the minimum gradient requirements. If you have a mass greater than the climb limit mass, the aeroplane will not have sufficient performance in the event of an engine failure to achieve the climb gradient requirements. So it’s a mass ceiling set by climb performance. The graph to calculate the climb limit mass is on page 11 of section 4 in CAP 698. We worked through an example in the previous chapter, but make sure you’re confident in using that graph. And the introduction to the climb section, on page 10 of section 4, reiterates the climb requirements. It states that during the take-off climb, the aeroplane must do two things: first, attain the most severe gradient requirement of the take-off net flight path, and second, avoid all obstacles in the obstacle accountability area by the statutory minimum vertical interval. So let me tie that together. The take-off flight path ends at 1500 ft, Segment 4 demands a minimum 1.2% gradient, and the climb limit mass is the mass ceiling that guarantees you can meet those gradients even with an engine failed. The two obligations — meeting the most severe gradient and clearing obstacles by the statutory margin — are what the climb section is built around. That’s the core of what you need to carry forward.