Page 43 - PDF_Flip_Book

Rod Machado’s Private/Commercial Pilot Handbook
14-20

and true south poles represent the spin
axis points of the earth. The earth acts like
a very large magnet (too big to put on any Fig. 31
refrigerator), and has two magnetic poles
(Figure 31). As I’ve previously stated, they
are, unfortunately, not located in the same
position as the true north pole. Lying just
a little north of Hudson Bay, the magnetic
north pole is separated by a distance of
approximately 1300 miles from the true
north pole.
The variation between these two poles
presents a slight challenge in navigation.
We measured our course with respect to
the true north pole, but we must navigate
using a compass that points to the magnet-
ic north pole. Fortunately, the answer is
simple—correct for the angular variation
between the true and the magnetic north
poles. This is easy to do once you under-
stand that this variation changes depend-
ing on your geographic location.
Figure 32 depicts an airplane in three
different locations across the United
States. In position B, the airplane is locat-
ed so the magnetic north pole is directly in
front of the true north pole. In this instance, both poles appear in line with one another, so there is no apparent varia-
tion in location between poles. Your true heading would be a magnetic heading at this location (a location with zero
variation). You could simply fly the number you found with the plotter on the compass (assuming no wind and the
compass is free of errors itself).
An airplane in position C views the magnetic north pole to the west (to the left) of the true north pole. We have
what is technically known as westerly variation between poles. The airplane in position A sees the magnetic pole locat-
ed to the east (to the right) of the true north pole. Airplane A experiences easterly variation between poles.
Clearly, the variation between poles depends on what part of the United States (or the world for that matter) you’re
in. Fortunately, we can correct for this variation since it’s a known quantity dependent on your location. Figure 33
shows the angular variation between the magnetic and true north poles. If you were flying along the western part of
Texas (Airplane C), the magnetic north pole would be 10 degrees to the east of the true north pole. Printed lines of

Fig. 32