Topographical Maps and Map Reading — Page 233, Lesson 215

I want to walk you through a genuinely dangerous trap in visual navigation — the "hill in front of the hill" situation. This is a classic error, and I want you to understand exactly why it happens, because it can cost you your clearance margin. Here's the scenario. You're flying toward rising terrain, and you see what you believe is the highest point ahead. You plan your altitude to clear it. But the terrain keeps rising behind that point, so the actual highest ground is hidden from your view — it's behind the hill you can see. That means your planned clearance may be considerably less than you intended. That's why it's called "the hill in front of the hill." The visible hill masks the higher ground behind it. And I want to stress — this is particularly dangerous when you're flying at lower altitudes, because you have far less margin to absorb the error. Now, let's talk about judging height, because that's a related skill that can fail you. Flying over a smooth water surface, over snow, or over a smooth desert surface makes it extremely difficult to judge your height. Why? Because your eyes need texture and features to gauge height, and those surfaces give you almost nothing. The difficulty gets worse over land when there are no features with vertical extent — for example, no trees. Here's the specific trap: in a desert or tundra landscape, you'll see bushes and scrub trees, and it's very easy to imagine they're full-size trees when they may actually be only a few metres high. So you think you're higher than you are, because you're scaling the world against trees that aren't really trees. Then there's the night problem. When you're flying over dark areas of sea or land where there are scattered pinpoints of light — ships, oil rigs, small settlements, isolated buildings — it's possible to become disorientated and confuse the scattered lights below with the scattered stars above. Your brain can't tell which lights are on the ground and which are in the sky. And this situation may be exacerbated after or during aircraft manoeuvres, when your spatial awareness is already being challenged by the motion. Now let's move to the navigation techniques themselves. The pilot navigation techniques and chart preparation requirements appropriate to visual navigation — including the 1:60 rule — are discussed in the relevant flight exercise briefings, so we'll cover those in detail when we get there. But the core principle I want to leave you with is this: a disciplined approach is always the most successful. Let me walk you through that discipline. When you set heading from a start point, or when you alter heading at a turning point, always check that you are flying the correct heading and that the compass is synchronized. Always check that you have the appropriate altimeter setting and are flying at a safe altitude. Always check that you have started or restarted your stopwatch, or that you know how much you are running early or late on planned time. That time check is your progress check — it tells you whether you're ahead of or behind your planned schedule. And finally, the most important piece of advice in this passage. Even the best navigators become occasionally uncertain of position. It is very tempting in that situation to carry on regardless. Don't. Start immediately — start your re-fix, your re-orientation, your correction — the moment you realise you're uncertain. Carrying on only compounds the error. That discipline is what separates a professional navigator from someone who gets lost.