Figure 12 - P-8010089

INSTRUMENT NAVIGATION

CORRECTTRG HACK TO THE ARC

As a guide, correct approximately 10 to 20 degrees for each 1/2 mile of deviation from the

desired arc. For example, under no-wind conditions, if the aircraft is 1/2 mile outside the arc and

the bearing pointer is 10 below the wing tip, the aircraft should be turned approximately 20

degrees toward the station to return to the arc. The actual amount of correction required for a

given error varies. Factors to consider are the size of the arc, ground speed of the aircraft

whether the aircraft is inside or outside the arc, etc. These factors affect the rate of deviation

from an arc and type of correction necessary to return to the arc. Remember that the curve of

small arcs is relatively "sharp," and corrections from the inside are assisted by the arc curving

toward the aircraft. Conversely, the aircraft outside a small arc requires larger corrections

because of the curvature away from the aircraft. Large arcs are easier to fly because of their

"flatter" curves. High speeds require more attention to maintain an arc because of higher rates of

deviation and correction.

So, in order to sta y on the 15 nm arc in the previous illustration (Figure 11) you'd

turn left. Since the head of the 02 needle had fallen 10 below the wingtip, you must

turn the aircraft 20 left, so that the needle will be 10 above the wingtip. As you

progress on your new heading, the needle will continue to fall. When it does, you will

simply turn 20 to ensure that it sta ys within 10 either side of the wingtip.

Figure 12

In the example above (Figure 12), the aircraft has just made its turn 20 to the left. It is still

on the 080 R but its flight path will bring it closer to the station, thus decreasing the DME. The

aircraft's path will cross radials, causing the head of the needle to fall.

TACAN POINT-TO-POINT 4-9