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line may extend for hundreds of miles, circumnavigation is not practical or even possible. If no other
course of action exists, the main objective is to avoid the more dangerous areas in the line.
7.24.8. Figure 7.21 shows an example of frontal penetration using radar. An iso-echo equipped radar can
discriminate between the safe and violent areas. Without it, decreasing the gain will work to highlight
the worst areas by leaving the densest water cells as the last returns on the PPI. Upon approaching the
line, the navigator determines an area which has weak or no returns and which is large enough to allow
avoidance of all intense returns by the recommended distances throughout penetration. The navigator
directs the aircraft to that point, making the penetration at right angles to the line so as to remain in the
bad weather areas for the shortest possible time. Avoid the dangerous echoes by a safe distance.
Penetration of a line of severe thunderstorms is always a potentially dangerous procedure. Attempt it
only when you must continue the flight and cannot circumnavigate the line. Always advise ARTCC of
your intentions when deviating from your flight-planned route.
Figure 7.21. Penetration of Thunderstorm Area.
196 AFPAM11-216 1 MARCH 2001
7.25. Heading Marker Correction. For optimum accuracy, it may sometimes become necessary to
correct the bearings taken on the various targets. This necessity arises when (1) the heading marker
reading does not agree with the TH of the aircraft when azimuth stabilization is used, or (2) the heading
marker reading does not agree with 360o when azimuth stabilization is not used.
EXAMPLE: If the TH is 125o and the heading marker reads 120o, all of the returns on the scope will
indicate a bearing that is 5o less than it should be. Therefore, if a target indicates a bearing of 50o, add 5o
to the bearing before plotting it. Conversely, if the heading marker reads 45o when the TH is 040o, all of
the scope returns will indicate a bearing that is 5o more than it should be. Therefore, if a target indicates
a bearing of 275o, subtract 5o from the bearing before plotting it. The greater the distance to the target
from the aircraft, the more important this heading marker correction becomes.
AFPAM11-216 1 MARCH 2001 197
Chapter 8
CELESTIAL CONCEPTS
Section 8A— Introduction to Celestial Concepts
8.1. Basics. Celestial navigation is a universal aid to dead reckoning (DR). Because it is available
worldwide and is independent of electronic equipment, it is a very reliable method of fixing the position
of the aircraft. It cannot be jammed and emanates no signals. Each celestial observation yields one line
of position (LOP). In the daytime, when the sun may be the only visible celestial body, a single LOP
may be all you can get. At night, when numerous bodies are available, LOPs obtained observing two or
more bodies may be crossed to determine a fix.
8.1.1. It is impossible to predict, in so many miles, the accuracy of a celestial fix. Celestial accuracy
depends on the navigator's skill, the type and condition of the equipment, and the weather. With the
increase in aircraft speed and range, celestial navigation is very demanding. Fixes must be plotted and
used as quickly as possible.
8.1.2. You don't have to be an astronomer or mathematician to establish a celestial LOP. Your ability to
use a sextant is a matter of practice, and specially designed celestial tables have reduced the
computations to simple arithmetic.
8.1.3. Although you don't need to understand astronomy in detail to establish an accurate celestial
position, celestial work and celestial LOPs mean more if you understand the basics of celestial
astronomy. Celestial astronomy includes the navigational bodies in the universe and their relative
motions. Although there are an infinite number of heavenly bodies, celestial navigation utilizes only 63
of them: 57 stars, the moon, the sun, Venus, Jupiter, Mars, and Saturn.
8.2. Assumptions. We make certain assumptions to simplify celestial navigation. These assumptions
help you obtain accurate LOPs without a detailed knowledge of celestial astronomy. However, celestial
positioning is more than extracting numbers from various books. A working knowledge of celestial
concepts will help you crosscheck your computations.
8.2.1. First, assume the earth is a perfect sphere. That puts every point on the earth's surface equidistant
from the center, forming the terrestrial sphere. Next, assume the terrestrial sphere is the center of an
infinite universe. Finally, assume all other bodies, except the moon, are an infinite distance from the
terrestrial sphere. Imagine them on the inside surface of an enormous concentric sphere, the celestial
sphere. If the stars, planets, and sun are infinitely distant from the earth's center, then the earth's surface
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