ADVANCED INSTRUMENT CONCEPTS
The purpose of this section is to provide the experienced RI student with greater comprehension
of selected radio instrument topics. Before delving into these concepts be sure that you have a
solid background in the basics of RI.
The information and techniques within this Appendix should not be viewed as required
procedures but as information to use in your execution of assigned maneuvers.
C101. RADIAL SPACING
You are no doubt familiar with the concept that as your distance from a NAVAID increases, the
spacing between given radials also increase. However, just how much does radial spacing
increase as you move from the station?
To answer this question, consider the following. At a distance of 60 NM from the station, there is
one mile between each radial. As you get closer to the station, the radials are closer together.
(For example, at 30 NM from the station, there is onehalf mile between radials or two radials per
mile; at 10 NM, it is 1/6 mile between radials, which equals six radials per mile. (Figure C1) In
general, 60 divided by distance from the station equals the number of radials per mile.
Figure C-1 Radial Spacing
C102. DISTANCE FROM AIRWAY CENTERLINE
Recall that a VOR Federal Airway is 8 NM wide, 4 NM on either side of the centerline. On
some occasions, it may be helpful to estimate your distance from airway centerline.
Again, merely convert angular distance to nautical miles by the same calculation used above,
e.g., 2º south of course at 30 NM from the TACAN station equates to 1 NM south of airway
ADVANCED INSTRUMENT CONCEPTS C-1