General Principles - Descent — Page 228, Lesson 270

We're now into the descent phase of the performance syllabus, and I want to look at how the wind affects your glide. This is a really practical piece of flying knowledge, so let's get into it. First, the headwind case. A headwind is bad for your descent range — it pushes you backwards relative to the ground, so you cover less ground for a given amount of height lost. Because of that adverse effect, in a glide it would benefit you to increase the aeroplane's forward speed slightly. Why? Because increasing your forward speed reduces the time you spend in the headwind. Less time in the headwind means the wind has less time to push you back, so you won't be pushed back as much. That's the logic — you trade a slightly higher speed for less total time exposed to the headwind. Now the tailwind case, and it's the mirror image. A tailwind benefits the glide because it increases your descent range — it pushes you forward, adding to your ground distance. So this time you want to stay in that situation for longer. You decrease the aeroplane's forward speed, which means you remain under the tailwind effect for a longer time, and therefore you get pushed further forwards. So the rule of thumb: headwind, speed up to minimise exposure; tailwind, slow down to maximise the time you're being helped. There's also a practical training point here. When you're flying a training sortie, make sure you know the wind speed and direction both for the surface and aloft. Surface wind and wind aloft can be quite different, and knowing both helps you plan a better descent, giving you more accurate circuit patterns. But more importantly, knowledge of what the wind is doing will ensure you obtain maximum descent performance if an engine failure should occur. That's the safety-critical reason for all of this — in a real engine failure, your glide performance is everything, and the wind is a major factor in how far you can actually go. Now, there are two practice questions that follow this, and they're the book's own questions. Let's try them one at a time.