Navigation errors, Track, Track made good, cross track error and corrections – the theory.

Consider an aircraft heading from A to C via point B where B is a fix point on the leg. Look at the diagram below.

Using the 1 in 60 rule the track error is the distance off track (cross track error) divided by the distance gone times 60 or:

            D-B x 60 = Track error
                A-B

Using the same calculation for the closing angle we get:

            D-B x 60 = closing angle
                B-C

Using simple maths and the rules of similar triangles, the heading correction at D to make point C is the sum of the track error and the closing angle:

Heading correction = D-B x 60 + D-B x 60
                                      A-B               B-C

Just remember that we're interested in the sum of the track error and the closing angle and not the formula! How we use it is covered in the next section.