Figure 20 - P-8010115

INSTRUMENT NAVIGATION

Figure 20

Continuing with our previous example, if we had commenced a ground speed check at our start

point, the 105R/40 DME, and 3 minutes later we found ourselves at the 078R/38 DME

(position number 2), our track would have been that of the dotted line. Our distance covered, the

actual length of that line, is 18 NM. Since our G/S check was for 3 minutes, we have covered 6

nm/Min, or 360 Kts G/S. Since our TAS is 420, we have a headwind component of 60 Kts.

To determine a G/S utilizing the pencil method, we employ a similar principle by connecting

the start point of our ground speed check to the stop point. Now compare the distance which

you have noted by the length of the pencil segment, to the radius of the BDHI. If you have done

it carefully, the proportion you determine should come out to 18 NM (Figure 21)

TACAN POINT-TO-POINT 5-17