Figure 22 - P-8010094

INSTRUMENT NAVIGATION

Figure 22

EXITING AN ARC

In this case (Figure 22), you are to intercept the 360R. Just as you lead your turns on an arc,

you must lead them off of the arc. The lead point is calculated in exactly the same manner as it

was to enter an arc.

Let's assume your ground speed is 300 kts. In this case, you would exit the arc 1.5 nm prior to

the 360 R. The question now arises, how do you determine 1.5 nm? After all, the DME has

been almost constant (15 + .5) for the past few minutes. To determine mileage you must refer

back to the old principle of distance between radials.

Since you are flying the 15 nm arc, you must determine the distance between radials at 15 nm:

15/60 = 1/4. Therefore, 1/4 nm separates each radial. You want to lead your turn by 1.5 nm,

so you must divide 1/4 into 1.5, which equals 6.

It is important to watch the rate of movement of your number two needle. As it approaches the

006 radial, turn to intercept the 360 radial.

WIND ON THE ACR

The previous discussion of arcing assumed NO WIND conditions. The wind will affect your

ability to navigate the arc. You must remember that, of the two aids (#2 needle and DME), the

DME is the more important. Regardless of the position of the #2 needle, you must endeavor to

keep the DME as close as possible to the DME of the arc. Therefore, if you were attempting to

fly the 15 DME arc and found yourself at 19 DME, you would turn toward the station until you

were at 15 DME. To ensure that you stay at 15 DME, you must crab. Also remember, as you're

turning your aircraft around the arc, the relative position of the wind will Change. A wind that

4-14 TACAN ARCING