COMPASS AND INERTIAL
NAVIGATION SYSTEMS
The material in this chapter is about aircraft
the movement of the aircraft to its intended
navigation systems. The basic systems discussed
destination.
are the aircraft compass system and inertial
navigation system (INS). Also, this chapter
DIRECTION
presents a discussion of the calibration of these
Direction is the position of one point in space
two systems.
relative to another, without reference to the
The way electrical signals are detected,
amplified, and delivered to various indicators and
distance between them. Direction may be either
systems is highly sophisticated. Before you begin
three-dimensional or two-dimensional; the hori-
zontal being the usual plane of the latter. For
this chapter, you might need to read Navy
Electricity and Electronics Training Series
example, the direction of San Francisco from New
(NEETS), Module 15, Principles of Synchros,
York is approximately west (two-dimensional).
Servos, and Gyros.
However, the direction of an aircraft from an
observer on the ground may be west and 20
above the horizontal (three-dimensional). Direc-
tion is not itself an angle (for example, the
NAVIGATION TERMS
direction east), but it is often measured in terms
AND DEFINITIONS
of its angular distance from a reference direction.
Learning Objective: Recognize the
COURSE
navigation-related terms and definitions
basic to compass and inertial navigation
Course is the intended horizontal direction of
system operation.
travel. For example, the direction of NAS
Jacksonville from NAS Pensacola is east. This
Any purposeful movement in the universe
should be the intended direction of flight.
involves an intention to proceed to a definite
However, because of wind conditions aloft,
point. Navigation is the business of proceeding
the aircraft might not head straight toward
so you will arrive at that point. Air navigation
Jacksonville, but somewhat to one side. No
is defined as the process of directing the
matter what the aircraft heading is, the course (the
movement of an aircraft from one point to
intended direction) is still east.
another. The function of air navigation is to locate
positions and measure distance and time along the
HEADING
intended direction of flight.
Heading is the horizontal direction in which
POSITION
an aircraft is pointing. In the previous example,
you can see the difference between course and
Position is a point defined by stated or
heading. Heading is the actual orientation of the
implied coordinates. You will frequently qualify
aircraft's longitudinal axis at any instant, while
this term by such adjectives as estimated, dead
course is the direction of travel intended. True
reckoning, no wind, etc. However qualified, the
heading uses the direction of the geographic North
word position always refers to some place that you
Pole as the reference. Magnetic heading uses the
can identify. One of the basic problems of the
direction of the earth's magnetic field at that
navigator is that of fixing his position. If he
location as the reference. Magnetic heading
does not know where he is, he can't direct
differs from true heading by the amount of
