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Chapter 4
DEAD RECKONING (DR)
Section 4A— Basic Navigation
4.1. Dead Reckoning (DR). Having discussed the basic instruments available to the navigator, we will
now review the mechanics of DR procedures, plotting, determining wind effect, and MB-4 computer
solutions. Using basic skills in DR procedures, a navigator can predict aircraft positions in the event
more reliable navigation equipment is unavailable or not operative. Therefore, a good foundation in DR
is imperative for the navigator.
4.2. Plotting. Chart work should be an accurate and graphic picture of the progress of the aircraft from
departure to destination and, with the log, should serve as a complete record of the flight. Thus, it also
follows that the navigator must be familiar with and use accepted standard symbols and labels on charts
as shown in Figure 4.1. (See Attachment 3 for additional chart and navigation symbols.)
Figure 4.1. Standard Plotting Symbols.
4.3. Terms Explained. Several terms have been mentioned in earlier portions of this pamphlet. Precise
definitions of these terms must now be understood before the mechanics of chart work are learned.
4.3.1. True Course (TC). The intended horizontal direction of travel over the surface of the earth,
expressed as an angle measured clockwise from true north (000o) through 360o.
4.3.2. Course Line. The horizontal component of the intended path of the aircraft comprising both
direction and magnitude or distance.
4.3.3. Track. The horizontal component of the actual path of the aircraft over the surface of the earth
Track may, but very seldom does, coincide with the TC or intended path of the aircraft. The difference
between the two is caused by an inability to predict perfectly all in-flight conditions.
4.3.4. True Heading (TH). The horizontal direction in which an aircraft is pointed. More precisely, it is
the angle measured clockwise from true north through 360o to the longitudinal axis of the aircraft. The
difference between track and TH is caused by wind and is called drift.
AFPAM11-216 1 MARCH 2001 113
4.3.5. Groundspeed (GS). The speed of the aircraft over the ground. It may be expressed in nautical
miles (NM), statute miles, or kilometers (km) per hour, but, as a navigator, you will use NM per hour
(knots).
4.3.6. True Airspeed (TAS). The rate of motion of an aircraft relative to the airmass surrounding it.
Since the airmass is usually in motion in relation to the ground, airspeed and GS seldom are the same.
4.3.7. Dead Reckoning Position (DR Position). A point in relation to the earth established by keeping
an accurate account of time, GS, and track since the last known position. It may also be defined as the
position obtained by applying wind effect to the TH and TAS of the aircraft.
4.3.8. Fix. A position determined from terrestrial, electronic, or astronomical data.
4.3.9. Air Position (AP). The location of the aircraft in relation to the airmass surrounding it. TH and
TAS are the components of the vector used to establish an AP.
4.3.10. Most Probable Position (MPP). A position determined with partial reference to a DR position
and partial reference to a fixing aid.
4.4. Plotting Equipment. A fine-tipped pencil, a good pair of dividers, and a plotter are imperative for
accurate chart work.
4.4.1. Dividers. Dividers should be manipulated with one hand, leaving the other free to use the plotter,
pencil, or chart as necessary. Some navigation dividers have a tension screw which you can adjust to
prevent the dividers from becoming either too stiff or too loose for convenient use. Adjust the points of
the dividers to approximately equal length. A small screwdriver, required for these adjustments, should
be a part of the navigator's equipment.
4.4.2. Plotter. A common plotter is shown in Figure 4.2. This plotter is a semicircular protractor with a
straight edge attached to it. A small hole at the base of the protractor portion indicates the center of the
arc of the angular scale. Two complete scales cover the outer edge of the protractor and are graduated in
degrees. An abbreviated inner scale measures the angle from the vertical (Figures 4.3 and 4.4). The
angle measured is the angle between the meridian and the straight line. The outer scale is used to read all
angles between north through east to south, and the inner scale is used to read all angles between south
through west to north.
4.5. Plotting Procedures for Mercator Charts:
4.5.1. Preparation. Many charts and plotting sheets are printed on the Mercator projection. Before
starting any plot, note the scale and projection of the chart and check the date to make sure that it is the
latest edition. The latitude scale is used to represent NM. The longitude scale should never be used to
　
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