We're in the middle of the take-off flight path segments now — Page 426, Lesson 528

We're in the middle of the take-off flight path segments now. We've already covered the first three segments — the ground roll, the initial climb with take-off thrust, and the segment where we accelerate and retract the flaps. So let's pick up with the end of that third segment and move into the fourth. In that third segment, the one where we're accelerating and retracting the flaps, there's no minimum climb gradient required. 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 we're not actually climbing at a set gradient, the performance standard we hold it to is that 1.2% figure. Now, segment four. The fourth segment 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 feet, and that's where the take-off flight path ends. Once you're above 1500 feet, the pilot will either recover to the airfield or continue to the take-off alternate. The climb gradient for this last stage must not be less than 1.2%. Now, these gradient requirements for Class A aeroplanes with more than two engines form part of the syllabus, so you need to remember them as well. We mentioned this in the previous chapter, but let me reinforce it: 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 engine failure to achieve the climb gradient requirements. 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 this graph. The introduction to the climb section, shown 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, it must attain the most severe gradient requirement of the take-off net flight path. Second, it must 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 is divided into segments, each with its own configuration and speed. Segment four is the final climb to above 1500 feet at maximum continuous thrust, with a minimum gradient of 1.2%. And the climb limit mass is the ceiling on your mass that guarantees you can meet those gradient requirements even with an engine failed. If you exceed it, you don't have the performance. That's the core of what you need to hold onto here.