Let me define the boundaries precisely, because the numbers matter — Page 426, Lesson 524

I want to walk you through the take-off climb for a Class A aeroplane. This is the phase of flight that starts right after you leave the runway surface and carries you up to the point where you're safely established in the climb. Let me define the boundaries precisely, because the numbers matter. The take-off climb, also called the take-off flight path, extends from 35 feet above the take-off surface up to 1500 feet above the take-off surface. That's the normal case. But there's an important exception: if you're doing a contaminated runway take-off, the take-off climb begins at 15 feet, not 35 feet. Contaminated means the runway has something on it like water, slush, or snow that degrades your performance, so the screen height drops. Now, that point on the ground directly below the 35-foot screen is given a special name: it's called "reference zero." Think of it as the origin point for measuring your obstacle clearance and your climb path. There are two main requirements that must be met within the take-off climb, and both are based on an engine failure occurring at VEF. Let me unpack that. VEF is the engine failure speed — the speed at which, if an engine fails, you've committed to continuing the take-off. Remember, for a Class A aeroplane — and Class A means multi-engine transport category aircraft — the performance must account for engine failure in all flight phases. So the take-off climb is designed around the assumption that you've lost an engine at VEF. The first requirement is that the aeroplane must be able to achieve the minimum climb gradients. The second requirement is that the aeroplane must be able to maintain sufficient obstacle clearance. And here's a critical distinction I want you to lock in: the climb gradient requirements are air-based gradients, while the obstacle clearance requirements use ground-based gradients. Air-based means relative to the air mass you're flying through; ground-based means relative to the actual ground, which matters when you're clearing obstacles like hills or towers. When assessing compliance with the regulations, the manufacturer or operator has a choice. They can use a continuous demonstrated take-off climb, or they can use a segmented take-off climb. Segmenting the climb makes the requirements and the procedure easier to comprehend, which is why most operators and manufacturers use the segmented profile — and that's what we'll use too. So let's look at the segments. The take-off climb is generally split into four unique segments, and I want you to see Figure 16.1 here, which shows the segments of the take-off climb for a typical Class A aeroplane. Each segment is characteristic of a distinct change in aeroplane configuration, speed, and/or thrust, with various actions and climb gradient requirements. So as you move from one segment to the next, something changes — maybe you retract the flaps, maybe you accelerate, maybe you reduce power. Each change defines a new segment, and each segment has its own climb gradient requirement you must meet. You'll need to learn what unique characteristics define each segment, because that's the heart of this chapter. We'll go through them one by one, but first make sure you've got the big picture: the take-off climb runs from 35 feet — or 15 feet on a contaminated runway — up to 1500 feet, measured from reference zero, and it's built around surviving an engine failure at VEF while meeting both your air-based climb gradients and your ground-based obstacle clearance.