Instrument Flight

Flight Procedures

It is sometimes necessary to change positions or radials inbound to or outbound from a facility. Both

inbound and outbound course intercepts are basically the same in that you must determine the angle of

intercept to achieve the most expeditious intercept of the desired radial.

The angle of intercept is the angle between the heading of your aircraft and the desired course; it is

normally greater than the number of degrees you are from your desired course, but it must not exceed 90

degrees. At 90 degrees, the rate of interception is the maximum possible. Within these two limits, you

can adjust your intercept angle to achieve the most desirable rate of interception.

Lead point for course intercepts is calculated as 1 percent of your estimated ground speed for an intercept

angle of 90 degrees. For intercept angles of 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

#22 and #24. You will calculate lead point either in radials or DME, depending on the maneuver you’re

performing.

The HSI 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 CDI also shows the relative speed at which you are approaching the desired course by

starting 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.

To perform a course intercept inbound to a station, first tune and identify the station (if you haven’t 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.

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