The following describes a step-by-step procedure for tracking to and from a VOR station using a CDI. Figure 16-32 illustrates the procedure.

[Figure 16-32]

First, tune the VOR receiver to the frequency of the selected VOR station. For example, 115.0 to receive Bravo VOR. Next, check the identifiers to verify that the desired VOR is being received. As soon as the VOR is properly tuned, the course deviation needle deflects either left or right. Then, rotate the azimuth dial to the course selector until the course deviation needle centers and the TO-FROM indicator indicates “TO.” If the needle centers with a “FROM” indication, the azimuth should be rotated 180° because, in this case, it is desired to fly “TO” the station. Now, turn the aircraft to the heading indicated on the VOR azimuth dial or course selector, 350° in this example.

If a heading of 350° is maintained with a wind from the right as shown, the aircraft drifts to the left of the intended track. As the aircraft drifts off course, the VOR course deviation needle gradually moves to the right of center or indicates the direction of the desired radial or track.

To return to the desired radial, the aircraft heading must be altered to the right. As the aircraft returns to the desired track, the deviation needle slowly returns to center. When centered, the aircraft is on the desired radial and a left turn must be made toward, but not to the original heading of 350° because a wind drift correction must be established. The amount of correction depends upon the strength of the wind. If the wind velocity is unknown, a trial-and-error method can be used to find the correct heading. Assume, for this example, a 10° correction for a heading of 360° is maintained.

While maintaining a heading of 360°, assume that the course deviation begins to move to the left. This means that the wind correction of 10° is too great and the aircraft is flying to the right of course. A slight turn to the left should be made to permit the aircraft to return to the desired radial.

When the deviation needle centers, a small wind drift correction of 5° or a heading correction of 355° should be flown. If this correction is adequate, the aircraft remains on the radial. If not, small variations in heading should be made to keep the needle centered and consequently keep the aircraft on the radial.

As the VOR station is passed, the course deviation needle fluctuates, then settles down, and the “TO” indication changes to “FROM.” If the aircraft passes to one side of the station, the needle deflects in the direction of the station as the indicator changes to “FROM.”

Generally, the same techniques apply when tracking outbound as those used for tracking inbound. If the intent is to fly over the station and track outbound on the reciprocal of the inbound radial, the course selector should not be changed. Corrections are made in the same manner to keep the needle centered. The only difference is that the omnidirectional range indicator indicates “FROM.”

If tracking outbound on a course other than the reciprocal of the inbound radial, this new course or radial must be set in the course selector and a turn made to intercept this course. After this course is reached, tracking procedures are the same as previously discussed.

Tips on Using the VOR

• Positively identify the station by its code or voice identification.

• Remember that VOR signals are “line-of-sight.” A weak signal or no signal at all is received if the aircraft is too low or too far from the station.

• When navigating to a station, determine the inbound radial and use this radial. Fly a heading that will maintain the course. If the aircraft drifts, fly a heading to re-intercept the course then apply a correction to compensate for wind drift.

• If minor needle fluctuations occur, avoid changing headings immediately. Wait a moment to see if the needle recenters; if it does not, then you must correctly recenter the course to the needle.

• When flying “TO” a station, always fly the selected course with a “TO” indication. When flying “FROM” a station, always fly the selected course with a “FROM” indication. If this is not done, the action of the course deviation needle is reversed. To further explain this reverse action, if the aircraft is flown toward a station with a “FROM” indication or away from a station with a “TO” indication, the course deviation needle indicates in a direction opposite to that which it should indicate. For example, if the aircraft drifts to the right of a radial being flown, the needle moves to the right or points away from the radial. If the aircraft drifts to the left of the radial being flown, the needle moves left or in the direction opposite of the radial.

• When navigating using the VOR, it is important to fly headings that maintain or re-intercept the course. Just turning toward the needle will cause overshooting the radial and flying an S turn to the left and right of course.

Time and Distance Check From a Station Using a CDI

To compute time and distance from a station using a CDI, first tune and identify the VOR station and determine the radial on which you are located. Then turn inbound and re-center the needle if necessary. Turn 90° left or right, of the inbound course, rotating the OBS to the nearest 10° increment opposite the direction of turn. Maintain heading and when the CDI centers, note the time. Maintaining the same heading, rotate the OBS 10° in the same direction as was done previously and note the elapsed time when the CDI again centers. Time and distance from the station is determined from the formula shown in Figure 16-34.

[Figure 16-34]

Course Intercept

Course interceptions are performed in most phases of instrument navigation. The equipment used varies, but an intercept heading must be flown that results in an angle or rate of intercept sufficient for solving a particular problem.

Rate of Intercept

Rate of intercept, seen by the aviator as bearing pointer or HSI movement, is a result of the following factors:

• The angle at which the aircraft is flown toward a desired course (angle of intercept)

• True airspeed and wind (GS)

• Distance from the station

Angle of Intercept

The angle of intercept is the angle between the heading of the aircraft (intercept heading) and the desired course. Controlling this angle by selection/adjustment of the intercept heading is the easiest and most effective way to control course interceptions. Angle of intercept must be greater than the degrees from course, but should not exceed 90°. Within this limit, make adjustments as needed, to achieve the most desirable rate of intercept.

When selecting an intercept heading, the key factor is the relationship between distance from the station and degrees from the course. Each degree, or radial, is 1 NM wide at a distance of 60 NM from the station. Width increases or decreases in proportion to the 60 NM distance. For example, 1 degree is 2 NM wide at 120 NM—and ½ NM wide at 30 NM. For a given GS and angle of intercept, the resultant rate of intercept varies according to the distance from the station. When selecting an intercept heading to form an angle of intercept, consider the following factors:

• Degrees from course

• Distance from the station

• True airspeed and wind (GS)

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