Figure 45

INSTRUMENT NAVIGATION

Figure 45

In Figure 45c the CDI is displaced to the left of center. This would suggest a left turn to

return to the desired course. However, examination of Figures 45a and 45b indicates a right turn

is necessary.

We can see that we appear to be getting conflicting information. The RMI shows a right turn

necessary to return to course - the CDI indicates a left turn.

This is a condition of the IND-350 known as "reverse sensing". Reverse sensing will occur

any time you twist a course with the OBS which lies in the lower half of the RMI, the case

illustrated in Figure 45. In some cases, this may be done deliberately with the intention of

immediately turning to a heading on which the IND-350 will provide proper sensing. In most

cases, however, reverse sensing will be the result of setting an improper course (probably 180

degrees off) with the OBS, which is the case in Figure 45.

To avoid reverse sensing make it a habit to orient yourself on the RMI and use the IND-350

in its proper secondary role. Make sure you have the proper course selected with the OBS,

remembering that if you track inbound to a station the course will be the reciprocal of the radial.

If you always remember to set the proper course with the OBS, the vertical bar (CDI) will always

tell you the direction to turn to return to course (i.e. if the bar is displayed to the left, turn left!)

SUMMARY

We have discussed the methods and procedures for determining courses, corrections to

courses and radials, and for maintaining these courses. We have also discussed drift, crab angle

and wind computations in relation to course control. Radial tracking is not limited to airways

navigation. All Standard Instrument Departures (SIDS) and instrument approaches involve some

form of radial tracking. You will find airways navigation will provide good practice and

discipline for these critical areas of flight.

3-34 RADIAL TRACKING AND COURSE CONTROL