Now, there are three key angles here — Page 199, Lesson 178

Let’s start with the diagram in Figure 11.2. I want you to picture a planned track — that’s the line you intend to fly over the ground, say 090° True. You fly a heading, which is the direction the aircraft’s nose points, and that heading is also 090° True in this example. But because of wind, the aircraft drifts sideways, so the path it actually makes over the ground — the track made good, or TMG — is different. In the diagram, the TMG is shown as 100° True, meaning the aircraft has been pushed to the right of the planned track. Now, there are three key angles here. The track error angle is the difference between the planned track and the TMG — that’s shown in green. In this example, the planned track is 090°, the TMG is 100°, so the track error angle is 10° to the right. The expected drift is the difference between the heading and the planned track — shown in red. If your heading is 090° and the planned track is also 090°, the expected drift is zero. But if you had calculated a heading of 092° to compensate for an expected 2° of drift, then the expected drift would be 2°. The actual drift is the difference between the heading and the TMG — shown in blue. Here, heading is 090°, TMG is 100°, so actual drift is 10° to the right. Here’s the important point: the track error angle is the difference between the expected drift and the actual drift. But track error angle is not drift itself. Drift is the angular difference between heading and track; track error angle is the angular difference between the planned track and the track made good. They are related, but they are not the same thing. That distinction matters when you start correcting. Now, we move into the 1 in 60 rule for navigation. There are three basic techniques for getting back to track. The first is the Double Track Angle Error method. The second is the Track Error Angle and Closing Angle method. The third is the Combined Track Error Angle and Closing Angle Single Calculation — which is just a faster variation of the second method. From these three, the Oxford preferred technique is called New Track Reference, but we’ll get to that later. Let’s work through the Double Track Angle Error method with an example. You plan to fly a track of 090° True. You do your flight plan, calculate a heading, and fly that heading accurately. After 30 nautical miles along the track, you get a pinpoint — a visual fix — that puts you 4 nautical miles left of track. First, calculate the track error angle. Using the 1 in 60 rule, 4 nautical miles off in 30 nautical miles along track gives you a track error angle of 8°. The rule says: off-track distance divided by distance along track, multiplied by 60, gives the angle in degrees. So 4 divided by 30 is 0.133, times 60 is 8°. So you are diverging from the planned track at an angle of 8° to the left. If you do nothing, you will continue to diverge from track at the same rate — you’ll get further and further left. So the first thing to do is stop that trend. You are diverging by 8° to the left, so you turn 8° to the right. That brings your heading parallel to the planned track. Now you are flying parallel to the planned track, 4 nautical miles left of it, and you are no longer diverging. That’s the first step in the Double Track Error Angle method — stop the divergence by turning through the track error angle.