Figure 31

INSTRUMENT NAVIGATION

Figure 31

In Figure 31, you are trying to fly J-39, but you are on the 195R of MGM. At 30 DME you

are left of course by 2 nm. Therefore, when you turn that aircraft to 020 to correct your

navigational error, you should realize that to get back on course you will have to cross 2 1/2 nm

of airspace. If the aircraft were on the same radial at 10 DME however, you would only have to

cross a little less than 1 nm of airspace. In this case, you are moving your aircraft the same

number of radials as in the first case. But, because the radials are more closely spaced nearer the

station, you would be back on course sooner since you will only be crossing 1 nm instead of 2

nm. Thus, the head of the #2 needle, would move toward 010 more quickly.

This correlation of distance from the station with the distance between radials must b e kept

in mind whenever making course corrections, otherwise the behavior of the #2 needle may

not be in accordance with your expectations.

The practical application of the above discussion deals with choosing the proper time to take

out the course correction and turn back to the original course. Based on the above examples, a

good rule of thumb is that when close to a station, you will be crossing radials rapidly; therefore,

you must take your correction out in time to avoid overshooting your course. When further

away, the radials are spaced further apart, so you can wait longer.

3-22 RADIAL TRACKING AND COURSE CONTROL