Figure 41

INSTRUMENT NAVIGATION

Until we know whether the course selected will take us TO or FROM that station, we cannot

orient ourselves. Consider the same situation with an operational TO-FROM indicator.

Figure 41

In Figure 41, the TO indicator is showing. This means that if you fly 180 degrees (course

selected by OBS) you will go to the navaid. This could only be possible if you were north of the

station as in Figure 41c. Figure 41b shows the FROM indicator with a course of 360 degrees set,

meaning that if you fly 360 degrees you will go FROM the station. Again only the situation

illustrated in Figure 41c satisfies these conditions.

Now we know that, in both the above depictions, the aircraft is located on the 360 degree

radial; i.e, due north of the station. This is so because a course of 360 degrees will take us

FROM the station and a course of 180 degrees will take us TO the station.

A problem remains, however, we have not yet discussed the aircraft's heading which is

completely independent of its momentary position. Let us continue with the above example.

Figure 42 shows one possible combination of aircraft heading and position.

Figure 42

3-32 RADIAL TRACKING AND COURSE CONTROL