Navigation Using the 1 in 60 Rule — Page 199, Lesson 180

I want to walk you through what happens after we've corrected a track error by turning onto a parallel track — and why that alone isn't good enough. So, imagine we've already turned 8° right to parallel our intended track. That stopped the problem from getting worse — we're now flying parallel to where we want to be, but we're 4 nautical miles to the left of it. We're not getting back to the track; we're just not drifting further away. Now, you might think: why not just turn a bit more — say another 10° right — and then use map-reading to find our way back? There are two problems with that. First, there might not be anything significant on the ground to tell us exactly when we've crossed back onto track. Second — and this is crucial — we don't want a navigation technique that demands continuous attention from the pilot. As a single pilot, you've got plenty to do: fly the aeroplane, monitor changing weather, think about fuel, make radio calls as appropriate, carry out engine and electrics checks periodically, and most importantly, look out to avoid other aircraft. We want a method that minimises the time spent actually navigating. We want a measured, controlled turn that tells us when we're back on track without having to map-read. So here's what we do instead. We turn another 8° right, making a total change of 16° right. Let me explain why that works. By turning through exactly double the track error angle — in this case, 16° right — we create what's called an isosceles triangle. The geometry is symmetrical about the cross-track error line. In the diagram, that cross-track error is marked as '4' — meaning 4 nautical miles. Because the triangle is isosceles, we're converging back to track at a closing angle of 8°. And here's the key: it takes the same distance to get back on track as it took to get off track. Therefore, the times will be the same. There may be a tiny difference because ground speeds aren't absolutely identical, but it will only be a matter of seconds — certainly less than a minute. Let me give you a concrete example. If I start off on track at 1000 hours and find myself off track at 1020, and I turn by double the track error angle, I will be back on track at 1040. No continuous map-reading required — all I have to do is look at my watch. But the story doesn't end there. If we do nothing about it once we re-cross our planned track — having turned 16° right at our pinpoint — we will now diverge to the right of track. We've solved the problem of getting back to track, but we haven't yet solved the problem of staying on track once we get there. That's what comes next.