less than 90 degrees, use an applicable ratio of this formula (e.g., a 45-degree intercept would require
one-third as much lead as a 90-degree intercept). See Figures 20 and 21. You will calculate lead point
either in radials or DME, depending on the maneuver youre performing.
The HSI display provides two indications that will assist you in determining lead point. First, the bearing
pointer will give you the relative speed at which you are approaching the desired course. By observing
the rate at which the bearing pointer approaches the desired course, you can determine when to initiate
your turn. Second, the course line provides the relative speed at which you are approaching the desired
course. The CDI course line starts to move once you are within 10 degrees of that course. When you are
60 nm from the station, the radials are 1 nm apart and at 30 nm, they are 1/2 nm apart. Therefore, the
CDI will move rapidly when you are close to a station and more slowly when the station is distant. Use the
HSI display scale selection and relative position of the aircraft symbol to the Planimetric course line to
judge the distance and intercept angle from the desired course.
To perform a course intercept inbound to a station, first tune and identify the station (if you havent already
done so) and then dial in the desired inbound course in the course select window. The two most used
procedures for accomplishing an inbound intercept are the 30-degree and the double angle off the bow
methods. When determining which intercept is most appropriate, consideration should be given to the
aircraft distance to the NAVAID (if known). A double angle off the bow intercept could be as little as 1 or
2 degrees or as much as 45 degrees. The 30-degree method is always 30 degrees. Consideration for
radial spread and closure rate determined by the distance from the NAVAID and wind should always be a
factor in the selection and application of an inbound intercept.
Once you have tuned the station and selected the desired course in the HSI display course select window,
look from the desired course on the compass card to the head of the bearing pointer used and 30 degrees
beyond. The heading located 30 degrees beyond the bearing pointer is the heading you will fly to the
intercept. Turn the aircraft to this heading and maintain it until you reach the lead point and then complete
the intercept (Figure 17). You look from the desired course to the bearing pointer.