Now, what makes an ideal visual checkpoint — Page 229, Lesson 208

I want to walk you through the principles of selecting visual checkpoints for navigation. This is a practical skill you'll use every time you fly visually, so let's get the details right. First, a key point: visual checkpoints do not need to be exactly on your planned track. A good feature that's close to your track is actually better than a poor feature that sits exactly on track. The reason is simple — if you can see a clear, recognizable landmark slightly off to one side, you can still use it to fix your position accurately. A poor feature on track that you can't identify or that looks like everything else around it gives you no useful information at all. Now, what makes an ideal visual checkpoint? The book gives us three characteristics to look for: large, unique, and having vertical extent. Let me take each one in turn. Large. A large feature will be recognizable from some distance away. That's the advantage. But here's the catch — if the feature is too large, it may be too big to use for precise navigation. You can't pinpoint your position against something that covers miles. The good principle here is to use part of a large feature as your actual checkpoint. For example, if you're using the city of Birmingham as a checkpoint, you'll see Birmingham from some distance, but don't just aim for "Birmingham." Instead, choose a large motorway junction within Birmingham as your accurate, precise checkpoint. That gives you the long-range recognition of the city plus the pinpoint accuracy of the junction. Unique. You must be absolutely sure that the checkpoint you choose could not be mistaken for a similar checkpoint in the same area. The book gives a classic example: disused airfields. They make good checkpoints in many parts of the country — they're often clearly visible, with runways and hardstanding still showing. But in East Anglia, there are so many disused airfields left over from World War Two USAF operations that it is easy to make mistakes. If every field you fly over has an old runway, you can't tell which one you're looking at. So uniqueness is critical. Vertical Extent. Features that have significant vertical extent — things like radio masts, television towers, mountains — should always be identified for safety reasons anyway. But they also make excellent visual checkpoints, particularly because you can identify them at some distance in good visibility. Let me give you the practical example the book uses. Imagine you can see a radio mast 20 miles away. You know you need to fly 1 mile to the right of that mast. You're flying at 120 knots. At 120 knots, covering 20 miles takes about 10 minutes. So by spotting that mast 20 miles out and knowing your offset, you have effectively solved the navigation problem for the next 10 minutes. You can spend that time checking your aircraft systems, keeping a good lookout, and enjoying the flight — you don't need to keep looking at your chart every 30 seconds. But there's an important limitation here. The value of features with good vertical extent alone may diminish as you fly higher. At 5,000 feet above ground level, you may not easily see a 400-foot-high mast. The mast's height becomes a smaller fraction of your altitude, and it blends into the ground more. So vertical extent is valuable, but you need to consider your altitude when deciding how useful it will be. Let me tie this together. When you're planning a visual navigation leg, you're looking for checkpoints that are large enough to see from a distance, unique enough that you won't confuse them with anything else, and tall enough to be visible at your cruising altitude. And remember — they don't have to be exactly on track. A good feature close to track beats a poor feature on track every time.