Direction
Direction is the second problem of navigation that we will discuss. Direction is defined
as the position of one point in space relative to another without reference to the distance
between them.
Point System
The usual reference point when discussing direction is true north, although others will
be used and discussed later in this chapter. The point system for specifying a direction
is not adequate for modern navigation. This system was used by simply stating the
cardinal point of the compass as the direction to travel. The cardinal points of the
compass are north, south, east, and west. When you use the point system, these
cardinal points are modified to achieve greater accuracy, for example; northeast, north-
northwest, southeast, etc.
Numerical System
Today, we use the numerical system for navigation. The numerical system divides the
horizon into 360 degrees, starting with north as 000 degrees and continuing clockwise
through east 090 degrees, south 180 degrees, west 270 degrees, and back north.
Magnetic Compass
As its name implies, the magnetic compass uses the force known as magnetism. Earth
has a magnetized core, two magnetic poles, and lines of force that form a magnetic
field. Like any other magnet, earth also has a north magnetic pole and a south magnetic
pole. Although the poles are placed at specific geographic sites on magnetic charts, the
locations of the magnetic poles change slightly at times.
As in a magnet, the lines of magnetic force running between the North and South Poles
create a magnetic field that affects any magnetic substance. As a result, a freely
suspended magnetic bar or needle tends to align itself with the earth s lines of magnetic
force.
The magnetic compass retains its importance despite the invention of the gyrocompass.
While the gyrocompass is an extremely accurate instrument, it is highly complex, is
dependent on an electrical power supply, and is subject to mechanical damage.
Conversely, the magnetic compass is entirely self-contained, fairly simple, and not
easily damaged.
Heading Determined by a Compass
Compasses are used to determine heading, which is the angle measured clockwise
from a reference point to the longitudinal axis of the aircraft.
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