File #1341: "Navigation and the Weather.pdf"

Navigation and the Weather.pdf

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Harold E. Mehrens
William E. Rowland
Art Director

The history of mankind is essentially a record of the
conquests he has made over his environment. Foremost
among such achievements has been his victories over the
obstacles he has met when traveling or conveying his possessions from one place to another. He devised the boat
with which he crossed the streams that lay in his path; he
developed the wheel which made easier the transportation
of his goods over land surfaces; finally, he invented the
airplane which enabled travel through the skies.
Early man found his way from one place to another
by means of prominent landmarks. When boats became
ships that sailed the seas and travel distances began to
increase, methods of navigation grew in complexity. Tod a y, n a v i g a t o r s e m p l o y t h e d e v i c e s o f r a d i o a n d e l e c tronics.
Ye t , w h e r e v e r m a n t r a v e l l e d , i n w h a t e v e r p e r i o d o f
time, he was concerned not only with finding his way
b u t a l s o w i t h t h e w e a t h e r. H e f o u n d t h a t t h e c i r c u m stances of the weather could prove a hindrance or a help.
As one travels the pathway of life, like the navigator
he must chart a course, and like the navigator he must be
alert to the circumstances which will affect the course he
charts. The complexities of modern life requires that
American youth be prepared to chart his life's course
The Civil Air Patrol is dedicated to the service of youth
in the age of aviation. Aware of youth needs, it has
prepared an aviation education series. It is our hope
and expectation that the information this series contains
will help young people plan and act so that they avoid
some of the hazards the future may hold.




Measuring Time, Distance & Direction




Dead Reckoning


Radio Flight & Celestial Navigation

The Weather


Air Masses, Fronts & Weather Hazards


Major General, USAF
National Commander
Civil Air Patrol

N a v i g a t i o n a n d t h e We a t h e r i s o n e o f a s e r i e s o f s i x
pocket-sized books prepared for use in the aviation education program of the Civil Air Patrol. It is to be used
with an instructional 35 mm. color, sound filmstrip illustrating the concepts it introduces.
The purpose of the book is to describe in terms of
secondary-school student understandings the types of
navigation, the principles and practices of each, and the
weather as a factor in navigation. The intent of the book
is not to present an exhaustive study of these areas.
Rather it is to help the student lay a foundation for further study in the fields of navigation and the weather
should his interests dictate such study. However, its content is sufficiently detailed to challenge the general interest of students and air-minded adults.
Although the first use of the book will be with Civil
Air Patrol cadets, it will be found to have other uses.
This book and the others of this series will be found
of value to students, teachers, and adult groups engaged
in any aviation-study program. This series is rich in information which provides both content for the secondary
school course in general aviation and materials for enriching the content of science and social studies classes.
The advice on technical matters received from the Civil
A i r P a t r o l H e a d q u a r t e r s , a l i c e o f O p e r a t i o n s a n d Tr a i n ing, and the advice on educational matters provided by
the Aviation Education Personnel helped materially in the
preparation of this book. Special acknowledgement is
also due to Mr. Irving Ripps of the Civil Air Patrol, Office
of Information Services, and to contributing members of
the Civil Air Patrol National Commander's Aviation Education Committee for suggestions and advice offered. The
names of the members of the three groups mentioned
above appear elsewhere in this booklet.
Director of Aviation Education
Weather charts and maps were made available through courtesy of the Weather
Bureau and the Civil Aeronautics Administration.


There are several tasks that every pilot performs before "take-off."
Among these are to (1) obtain proper charts, (2) check the weather,
(3) compute the range of his plane and select refueling points, (4)
lay out his course, (5) study the chart for landmarks and (6) file a
flight plan. Two of these tasks which require first attention are (1) to
chart his course and (2) to learn the kind of weather he will likely
encounter along his route.
The importance of the aeronautical chart.
In order to chart his course properly, the pilot needs to have the right
kind of instruments, an understanding of the proper procedures, and
the proper sectional or world aeronautical charts. A pilot so
equipped uses pencil, scale, and protractor or plotter (1) to draw a
true course line or lines from his point of departure to his

Plotting the Course

(2) to mark check points along this line, (3) to measure the distance
from his point of departure to each, and (4) to find the direction of
each course line drawn. He must also learn from the chart (1) the
location of danger areas and restricted areas (such as Air Defense
Identification Zone (ADIZ) areas), (2) land marks, (3) the nature of
the terrain (the earth's surface) over which his flight will take place
and,(4) "man-made" obstacles to safe flight.
Aeronautical charts are published by the United States Coast and
Geodetic Survey. Three types of aeronautical charts are most useful
in air navigation: the Sectional Charts (scale, 8 statute* miles to an
inch), the World Air Charts (scale, 16 statute miles to an inch), and
the Aeronautical Planning Charts (scale, 80 miles to an inch).
The importance of weather information.
A pilot cannot chart a proper course unless he knows something of
the prevailing weather conditions or those likely to occur along the
path of his flight.
He may under certain conditions (for example, Visual Flight Rules)
plan his course so that his flight avoids clouds, fog, or blowing dust
which would obscure the surface over which he flies. He must
always take into account the effect of the wind upon his flight and
take advantage of favorable winds. In fact (as you will soon
discover) the speed and direction of the wind are very important
factors in navigation.
Unless a pilot knows the wind conditions affecting his flight, he
cannot solve navigation problems involving (1) compass headings,
(2) wind drift, (3) ground speed, (4) climb and descent time, and (5)
fuel consumption in relation to distance flown.
As a matter of fact, information about the weather is so important to
safe flight that radio-range signals are interrupted periodically so
that weather information can be broadcast to pilots in flight.
Moreover, a pilot in flight may obtain weather information from any
radio communication station.
Before beginning a flight operation, pilots may obtain information
from the Weather Bureau, from Flight Information Service, or, in the
case of airline pilots, from the airlines' meteorological service. Such
information is communicated not only directly and by means of
radio, but also by means of maps and reports.
A statute mile is 5,280 feet. A nautical mile is 6,080 feet, or 1/60 of
a degree of the earth's equator.

The role of the pilot in weather forecasting.
The fact that weather information is so readily available to the pilot
does not mean that his only responsibility in terms of weather is to
check with weather information services. He must also know how to
interpret the weather information he receives. Before he can do this
he must understand the map and report symbols used by
Again, the weather factors used by meteorologists when they make
weather forecasts are so complex that forecasts are subject to
continuing amendment. By reason of this same complexity of
weather factors, unexpected weather changes are always a
possibility. Consequently, pilots must know, and all of us should
know, the signposts of the weather such as different cloud types.
Pilots also should be able, on the basis of current weather data, to
foresee weather conditions--such as fogs, thunderstorms, and icing
conditions which might prove hazardous to safe flight.
The importance of weather charts.
Weather charts are published by the United States Weather Bureau.
Among the most important of these are Surface Weather Maps,
Winds Aloft Charts, Constant Pressure Charts, and Prognostic
Charts. Surface Weather Maps are prepared from weather
observations taken simultaneously at 0130, 0730, 1330, and 1930,
Eastern Standard Time by the several hundred U. S. Weather
Observation Stations; Winds Aloft Charts are prepared four times
each day from information supplied by approximately 125 stations
spaced throughout the United Slates; Constant Pressure Charts and
the Prognostic Charts help discover changes in the weather pattern
that will be important to flight operations.
Although weather charts are of importance to pilots, they are of
greater importance as the tools which enable meteorologists to
make their forecasts. Moreover, important as weather charts are to
pilots, of greater importance are the weather sequence reports*
from stations along the flight path and the weather forecasts
covering the route to be flown and the airports at which landings are
intended. It is interesting and significant that in addition to reports
from weather stations, reports of weather encountered by pilots in
flight (PIREPS) ore used by weather forecasters. As a matter of fact,
pilots must be always aware of the
*Weather reports which are prepared in a continuing series.

current state of the weather. All flight planning and all navigation types must
take wind and weather factors into consideration. Unless this is done, a
proper VFR (Visual Flight Rules) course cannot be charted; a proper
compass heading cannot be determined; the ground speed and time of
arrival at a proposed airport cannot be calculated.
Types of Navigation





Ty p e s o f n a v i g a t i o n .
Aerial navigation is the science of flying from one place to another
a s d i r e c t l y a s c i r c u m s t a n c e s w i l l a l l o w. A p a r t o f t h e fl i g h t p r o c e d u r e
can be planned in advance. However, since all the circumstances surrounding a flight cannot be predicted, another part of the flight procedure must be decided as unexpected conditions are encountered.
One way to keep an aircraft on its course is by reference to visible
landmarks which are known to mark the desired flight path. This type
of navigation is called piloting or pilotage. Another type is to calculate
a compass heading in advance of the flight, then keep a careful record
of the direction, distance, and time of flight between positions along the
course In this type of navigation, called dead reckoning, compass
headings may have to be changed from time to time, during flight, in
o r d e r t o c o m p e n s a t e f o r t h e e ff e c t o f t h e w i n d a n d k e e p t h e a i r c r a f t
on course.
Proper radio equipment enables the pilot to take advantage of the
network of four-course ranges, and omni-ranges that mark the designated airways covering the country. (See Airports, Airways, and Electronics, Chapter V). This type of navigation is called radio navigation.
Navigators skilled in the procedure can determine the position of a
ship on the water or an airplane in the air by means of observing the
position in the heavens of the sun, stars, or planets. This type of navigation is called celestial navigation.
One type of navigation is generally used in conjunction with another.
The longer the flight, the more likely that several navigation methods
will be employed. On flights across the ocean, celestial navigation
plays its greatest role. Although some intercontinental flights, like that
of Lindbergh from New York to Paris, have been by piloting and dead
r e c k o n i n g , t o d a y, n a v i g a t o r s a n d p i l o t s o n s u c h fl i g h t s a r e l i k e l y t o
employ all four navigation types.


Everyone who has studied elementary science knows that the earth moves
around the sun in an elliptical path known as the earth's orbit.
We all know that, it also revolves an its axis once every 24 hours. An
interesting fact about this axis is that it tilts about 23 1/2 in relation to the
plane of the earth's orbit. This circumstance accounts for the change of
seasons as the earth follows its yearly path around the sun. Of special
interest at this time, however, is that the ends of the earth's axis, called the
poles, provide us with convenient points upon which to build a system of
Meridians of longitude and parallels of latitude.
Midway between the poles is the Equator. It is an imaginary line formed by
a plane intersecting (cutting through) the exact center of the earth
perpendicular to another plane intersecting the poles. The Equator is the
only great circle which can be perpendicular to a plane inter1 As used in mathematics, the term, plane, is defined as a surface having
length and breadth, but not thickness. Although a thin sheet of paper is
actually a solid, because of its thinness, it may be used to illustrate the
mathematical concept of a plane.
2 A great circle of the earth is a path described on the earth's surface by a
plane passing through its exact center, as the Equator or any Meridian of

secting the poles. However, any number of planes defining great
circles can be constructed perpendicular to the plane of the Equator
and still intersect (or contain) the poles.
The circles around the surface of the earth defined by constructing
such planes are called meridians of longitude; other circles around
the earth which parallel the Equator are called parallels of latitude. In
order to use meridians and parallels to indicate position on the earth's
surface, reference points are chosen. These are provided by the
prime meridian which passes through Greenwich, England, and the
Since meridians and parallels are circles, and circles are usually
divided into 360 parts called degrees, we speak of Lat. 45° N.or S.
and Long. 90° E or W. The degree used in this way is a unit of angular
measurement. The angular distance from the Greenwich meridian
around the world and back is 360°. Since points from Greenwich are
measured up to 180° east or west, no point can be at an angular
position from Greenwich of more than 180°. Likewise since the
angular distance from the Equator to either pole is 90° (rather than
1/2 of 360°), no point can have a latitude position greater than 90°.
The position of any place on the surface of the earth can be
expressed in degrees longitude and latitude. The position of New York
City, New York is approximately Lat. 40° N., Long. 74° W. The position
of Sydney, Australia is approximately Lat. 30° S., Long. 150° E.
As an hour is divided into minutes and seconds, an angular degree
can also be divided into minutes and seconds. A minute in this
instance is one-sixtieth (1/60) part of an angular degree; a second,
one sixtieth (1/60) part of an angular minute.* Using angular minutes
and seconds in addition to degrees, make it possible to locate the
positions of places upon the surface of the earth quite accurately.
Everyone knows that a day is defined as the length of time it lakes for
the earth to make a complete revolution. During each revolution any
point on the earth's surface will travel a circular path of 360°.
Since there are 24 hours in a aay, in one hour such a point will travel
360°/24 or 15%
Since noon is defined as the time of day at which the sun is directly
above a meridian, twelve o'clock noon (and consequently every hour *
Although a.statute mile is 5,280 feel, a nautical mile is 6,080.2 feet
(1853.3 meters).
The nautical mile is 1/60 of a degree of the earth's equator (one

of the day) sun-time differs for every meridian. The sun crosses
these only one at a time.
As a result of these circumstances and the confusion that would
otherwise result, it has become common practice to establish time
belts for each 15° of longitude, each having a difference in time of
one hour between them. Since the United States lies between 67°
and 125° west longitude (Long. 67° W. and Long. 125° W.), the
angular distance across it is 125° - 67° or 58:. Consequently, it is
found convenient to divide continental United States into four time
belts--Eastern, Central, Mountain, and Pacific. When the sun lies
above Long. 75° W., it is noon Eastern Standard Time (1200 hours)
throughout the Eastern Time Belt; 11:00 A.M. Central Standard
Time (1100 hours) throughout the Central Time Belt; 10:00 A.M.
Mountain Standard Time (1000 hours) throughout the Mountain
Time Belt; and 9:00 A.M. Pacific Standard Time (0900 hours)
throughout the Pacific Time Belt. As the sun crosses Long. 90° W., it
becomes noon throughout the Central Time Belt with corresponding
time changes within the other three time belts. Noon occurs
throughout the Mountain Time Belt when the sun crosses Long.
105° W.; and throughout the Pacific Time Belt, when the sun
crosses Long. 120° W.
You will discover that the dividing lines between the time zones
sometimes are irregular and do not coincide exactly with the
appropriate meridian. These irregularities result because
communities near time-belt boundaries find it convenient to use the
time schedule of a neighboring trade center.
Map projections and aeronautical charts.
The great problem of map and chart making (cartography) is to
represent the spherical surface of the earth on a flat map or chart so
that positions may be fixed and distances measured accurately. If
you have ever tried to flatten the cover of a baseball, you know how
difficult is the task of the map maker (cartographer). The ideal map,
which has never been realized, would be of true shape (conformal),
true size (equal area) and true direction (azimuthal).
Cartographers have devised a number of methods by which they
solve (for all practical purposes) this problem. Obviously the
purpose for which a map or chart is to be used determines to some
extent the method of its construction. Three projections or methods
of map making are most commonly practiced. These are the
cylindrical, the conic, and the gonomonic projections.

Imagine a transparent globe of the earth, including its geographical
figures and lines of longitude and latitude, with a lighted electric light
bulb in its exact center. If a rectangular sheet of paper is wrapped
around this globe so that it forms a cylinder, the light will cause the
areas and lines of the globe to be projected on the cylinder. If these
areas and lines are traced on the paper and the paper unrolled, a
cylindrical map projection will result.
If a paper cone is placed over this globe and the projected areas and
lines traced on the paper, the result will be a conic projection.
If a circular sheet of paper is placed tangent to (touching) the globe,
and the projected areas and lines traced on the paper, the result will
be a gonomonic projection. A comparison of these projections with
the globe will show that in each projection there are certain
The Mercator Map.
The most noticeable characteristics of the Mercator Map are (1) the
meridians are vertical, (2) the parallels horizontal, and (3) that the
separation of these increase as they approach the poles. Although
the Mercator projection shows the true shape of each area (is
conformal), it does not represent each in proper proportion one to
another (is not an equal area projection). Neither is the mercator a
true direction projection (does not show the true bearing or azimuth
of one place from another).
1 Gonomonic (pronounced no-mon'ik) means "that which knows". It
shows true direction. Its use is in long range flying.
2 The Mercator Map was devised in 1569 by a Fleming (a Northern
Belgian) Gerhard Kramer, who called himself Mercator.

The chief advantage of the Mercator is that it shows true compass
direction. A straight line drawn between any two points on this
projection will show the constant compass course between them
(see page 11). This line is called the rhumb line. A line drawn on a
globe so that it crosses each meridian always at the same angle in
order to maintain a constant direction would assume the shape of a
spiral curve (Ioxodrome). Obviously a rhumb line is not the shortest
distance between two points on the surface of the earth. A great
circle route is the shortest distance between two such points.
However, when the magnetic compass is used as the direction
finder, the only way the navigator can follow a great circle route is to
plot his course as a series of short rhumb lines. (See page 13.)
The Lambert Conformal Conic Projection.
The Lambert Conformal Conic Map or Chart is projected on a cone
which intersects the globe on two parallels of latitude. It shows the
true shape of areas between the parallels, but only on the two
parallels are areas accurately represented. Between the two
parallels, the areas are somewhat smaller than those on the globe;
outside the parallels, somewhat larger. However, the scale error is
always small.
Meridians and parallels intersect at right angles on the Lambert
Chart and their relationship with those on the globe are always
constant for all directions. You will observe that parallels of latitude
appear on the Lambert Chart as curved lines.

On the Lambert Map or Chart, a great circle may be represented
by a straight line. The maps prepared by the U. S. Coast and
Geodetic Survey to meet the needs of aerial navigation use the
conformal conic projection. Both Sectional Charts and World Air
Charts represent small sections of larger areas. Such charts fit
together accurately. Each contains a wealth of aeronautical data
pertaining to course plotting and navigating.
Directions on a chart are measured in angular degrees, minutes,
or seconds. The bearing (direction) of one place from another is
always measured clockwise from North. Hence a place due east
of you would bear 90°; one due south, 180°; one due west, 270°.
If you measure the angle formed by the line drawn on the chart
and the meridian of your position, you will find the direction or
bearing of the place to which you want to go. However, on the
aeronautical charts in common use, the line you have drawn will
not cross all meridians at the same angle. If you wanted to fly
from New York to San Francisco, and measured the bearing of
New York on an aeronautical chart, you would find it to be 282°.
However, if you take a bearing on San Francisco from the
Meridian half way along your course line, you will find this to be
265°. It is a common practice to break up long flights into legs of
3° or 4° of longitude, and to measure the angular direction of
each leg at its mid-meridian.
Measuring the True Course





Measuring a true course (TC).
It is quite easy to find the direction of the course to be followed in
flight. A line is drawn from the point of departure to the destination of
the flight. Then a measurement is taken of the angle this line makes
with the meridian midway between these points. This measurement
is the true course (TC) direction. It is not necessarily the direction
(TH) toward which the nose of the airplane is pointed in order to
offset the effect of the wind and make good the TC.
The compass rose printed on the aeronautical chart may be used to
measure course direction. An instrument called a protractor or one
called a plotter which incorporates a protractor serves this purpose
even better than the compass rose. Both the compass rose and
protractors are marked off in degrees (units for measuring direction).
If the difference in longitude between the points of departure and
destination is not more than 3° or 4° , the course should be
measured at its mid-meridian. If the difference in longitude between
this point is greater than 4°, then the course should be divided into a
series of courses, each crossing not more than 4° of longitude. In
this latter instance the true course (TC) direction of each coursesegment will become the basis for the heading of the aircraft during
its flight along such course-segment.
In order to measure the direction of a course or course-segment,
the protractor should be placed with the mid point of its base at the
intersection of the course line and the mid-meridian and its 360°
mark (N) on the mid-meridian. Since a course is measured
clockwise from N, read the direction in degrees on the curve of the
protractor where it is intersected by the course line. You will observe
that should a course be in the direction of 40°, the return course
would be in the direction of 220°. Should it be in the direction of
192°, the return course would be in the direction of 12°. There is
always 180° difference between a course and its reciprocal (return
course). To find the reciprocal of a course less than 180°, one must
add 180°. To find the reciprocal of a course 180° or greater, one
must subtract 180°.
Magnetic meridians and magnetic courses.
The true course when there is no wind blowing is the true heading
of an aircraft in flight. However, there is generally a variation
between the true heading and the heading indicated by the
magnetic compass.
This condition exists because the magnetic poles do not coincide
with the poles defined by the earth's axis. The north magnetic pole

Magnetic Meridians
located near Lat. 71° N., and Long. 96° W., about 1300 miles from
the geographic north pole.
On aeronautical charts the degree and direction of magnetic
variation are shown by magnetic meridians called isogonic lines.
Such lines connecting points of equal magnetic variation, are likely
to be irregular, and extend from the north to the south magnetic
pole. Points at which there is no magnetic variation are joined by a
line called an agonic line.
Isogonic lines show the general direction toward which a compass
needle will point.
At San Francisco, the variation is 18° E. Since this means that the
compass needle points 18° East of true north, a pilot, to fly a true
heading* of north in the San Francisco area, must fly a magnetic
heading of 342° (360° — 18°). To find the magnetic course
corresponding to any true course in the San Francisco area one
must subtract 18° from the amount of the true course. To fly east in
this area, a pilot must use a magnetic course of 72° (90° -- 18°). To
fly a true course of 118°, he must use a magnetic course of 100°.
At New York, the variation is 11° W. Since this means that the
compass needle points 11° west of true north, a pilot, to fly a true
heading of north, must fly a magnetic heading of 11 (0° + 11°).
All heading calculations used are based upon a "no-wlnd" condition.

To find the magnetic course corresponding to any true course in the
New York area, one must add 11° to the amount of the true course.
The pilot remembers that to convert true direction to magnetic
direction, he must note the variation shown by the proper isogonic
line on his chart. If the variation is east, he must then subtract the
variation from the true direction; if it is west he must add the
variation to the true direction.
The basic navigation instruments.
As aviation develops and aviation activities become more complex,
new navigation instruments are developed. The modern aircraft
used in military or air transport operations employ many navigation
instruments. However only four of these are indispensable in
piloting and dead reckoning. These are the clock, the air speed
indicator, the magnetic compass, and the altimeter.
The clock, or watch, is used to measure the elapse of time between
check points. Hence, it is essential when a pilot wants to learn the
ground speed of his airplane in flight, estimate arrival time, and
compute fuel consumption. The potential energy of a coiled spring
operates the mechanism of the clock, or watch; uniform speed of
operation is obtained by means of a balance wheel.
The airspeed indicator is used to measure the speed of the aircraft
through the air. (Not its speed over the ground.) Its operation
depends upon the difference between the pressure of air in motion,
as registered by the pitot tube, and the air contained in the
instrument case of the air speed indicator. (See Aircraft in Flight,
page 51.) At any considerable altitude, since the comparative air
density is low, the indicated airspeed reading is too low. True
airspeed can be approximated by adding 2% of the indicated
airspeed for each 1000 feet of elevation above standard sea level.
The magnetic compass is used to determine direction. Its operation
is based upon the attraction that the earth's magnetic poles has for
the compass needle. A compass card is attached to the needle.
Excessive swinging of the compass card and needle is dampened
by a light oil which fills the compass case.
The magnetic compass does not indicate true directions for three
possible reasons: 1. A geographic pole and its corresponding
magnetic pole are not at the same place. 2. Local ore deposits
influence com-

Basic Navigation Instruments

pass action. 3. The engine and other aircraft parts and equipment.
affect compass operation.*
A directional gyroscope is often used with a magnetic compass. It
employs the principle of gyroscopic inertia. Gyroscopic inertia means
that a gyroscope, as long as its wheel is revolving, tends to remain in
the same position and plane of rotation--that is, regardless of the
heading the aircraft assumes, it tends to keep its original direction.
It is more accurate than a magnetic compass during turns in flight, but
because of precession (a tendency to advance), it needs to be reset at
fifteen minute intervals.
The altimeter measures altitude. Its operation is based upon the fact
that as altitude increases air pressure decreases. The variations in the
air pressure upon a hollow sealed diaphragm activates an indicator
needle. This needle records pressure altitude as feet above sea level.
To obtain exact altimeter readings the indicated reading must be
corrected for current atmospheric pressure and temperature
Altimeters read correctly only when sea level temperature is 59°F. and
the temperature decrease per each 1000 feet of altitude is 3.6°F.
It also takes the altimeter a few seconds to record changes taking
place in an aircraft's elevation. This characteristic is called altimeter
Reading a chart.
You have already learned that the chart used in air navigation contains
much important information. Some of this information deals with
landmarks which the pilot uses to check his position. Some of this
information helps the pilot when he is planning his course.
A compass correction chart is placed in the cockpit of every aircraft to
show the compass deviation for such aircraft.

In order to indicate landmarks, such as cities and towns, highways,
railways, rivers, swamps, mines, lookout towers, and the like, standard
s y m b o l s a r e u s e d . ( S e e i l l u s t r a t i o n b e l o w. ) I n o r d e r t o i n d i c a t e
topography (the size, shape, and position of features of the earth's
surface), contour lines and colors are used. Contour lines are drawn
so that each line passes through places, all of which have the same
e l e v a t i o n a b o v e s e a l e v e l . T h e c l o s e r t h e c o n t o u r l i n e s a r e t o g e t h e r,
the steeper the elevation. On the aeronautical chart, elevations from
0 to 1000 are shown in green; those from 1000 to 2000, in light
green. Elevations from 2000 to 3000 are shown in light brown.
As elevations increase the shades of brown become increasingly darker.
the points of highest elevation are marked by a small, black dot and a
number designating its height in feet.
Reading the Chart


“Before take-off” navigation procedures.
It is common practice for pilots to plan their flights in advance.
Should the aircraft a pilot is to fly have neither radio transmitter nor
receiver, the flight planned will likely be navigated by means of
pilotage, dead reckoning, or a combination of these two methods. In
any of these instances, the aircraft must have a magnetic compass,
an airspeed indicator, and an altimeter; and the pilot must have an
accurate watch.
If an aircraft has no radio equipment, it is restricted to visual flight
rules (VFR} operations. Consequently, the planning of a flight under
these circumstances must take VFR weather minimums into
The "before take-off" procedure undertaken by a pilot is the same,
up to a point, for both pilotage and dead reckoning. 1. On the chart
that he uses, the pilot draws a line from the location representing
the point of his departure to that which represents his destination.
This is the true course line, and its angular direction measured at its
mid-meridian will give the direction of the true course (TC). See
page 13.) 2. He "marks-off" the true course line in segments
representing distances of 10 miles (when more convenient, other
distances may be used). 3. He selects land marks along or near his
route to use as "check points". The first of these should be a
prominent land mark near the airport. However, it should be far
enough from the airport, so that the aircraft before reaching it will
have left the airport traffic pattern and reached its cruising altitude.
These check points are used by the pilot to help ascertain the
ground speed of his aircraft and to keep it on the proper heading. 4.
He must now select suitable "brackets"" near enough to the course
to be easily seen. Whenever
* A bracket is a terrain feature such as a railway, river, or prominent
highway which parallels a course, or a portion of a course.

possible, brackets should be indicated along both sides of the
course line. End brackets should also be marked. These help
prevent "overflying" the airport of destination. 5. The pilot next
measures the direction of the true course. (See page 13.) 6. The
pilot finally finds the compass course by taking into account both
magnetic variation and compass deviation.
A flight by pilotage.
If you are a pilot planning to navigate a flight by pilotage and have
completed these six steps you are ready to begin your flight and to
follow the steps of procedure required by the in-flight phase of
Pilotage: 1.
As soon as your aircraft leaves the airport and reaches the first
check point, place it on the proper compass course. 2. Observe the
direction in which the wind is drifting your aircraft, using the drift
meter if your aircraft is equipped with one. 3. Correct the heading so
that the aircraft's direction as determined by your reference points
corresponds to that of the TC line. 4. Note the elapsed time between
your first and second check points and determine your ground
speed. 5. Keep a continuous check on the position of your flight by
means of check points and brackets.
Assume that you have just completed a flight from Bowman Field at
Louisville to Cincinnati-Lunken Airport navigating by pilotage. Before
beginning the flight you found your magnetic course to be 47°.
However, the compass correction chart in the cockpit of your aircraft
reads as follows:

(MH) N 30 60 E 120 150 S 210 240 W 300 330
(CH) 0 29 57 86 117 149 180 211 243 274 303 334

Consequently, after you left your first check point, you headed your
aircraft toward 45° (47° - 20).* Had your flight from Louisville to
Cincinnati been an actual rather than an assumed one, a report of your
subsequent experience could have been quite similar to the following:
1. As you passed your first check point after leaving Bowman Field, you
checked your watch and observed the hour to be 10:00 a.m. At 10:10
you found that the position of your aircraft was over a railway, 2 or 3
miles on the right of your course line. You also observed that your
position was about midway between two towns, which you identified as
Pewee Valley and Crestwood. You rightly concluded that the wind had
drifted you off-course and that you should correct your heading.
Consequently, you changed your compass heading (CH) from 45° to
43°, assuming that such an amended heading into the wind would put
you over La Grange after a further time elapse of four or five minutes.
However, at 10:15 you discovered La Grange on your left, and that the
wind was still drifting your aircraft off course to the right. Consequently,
you made still another CH correction. You now aligned your aircraft on a
CH of 38° with landmarks which, according to your chart, appeared to
be on a new direct course from your present position to CincinnatiLunken Airport. At approximately 10:24 a.m. your position was directly
over Campbellsburg, one of these landmarks. You held a heading of
38° for the next ten minutes and discovered that you were exactly on
course. You reached Cincinnati-Lunken Airport at 11:05 a.m.
and circled the airport, landing after you got a green light from the
control tower.

* In order Io determine the CH (45°) it is necessary to interpolate (determine average).
MH47° lies approximately half way between 30° and 60°. The compass heading correction necessary
lies between 1° (MH30°--CH29°) and 3° (MH60°--CH5°). The average therefore is approximately 2°;
hence (47° - 2°) = 45°CH.


T h e W i n d Ve c t o r D i a g r a m

A pilot using dead reckoning to navigate the course from Bowman
Field to Cincinnati-Lunken Airport, would have taken an additional
step in his "before take-off" procedure. He would have converted the
magnetic course to a magnetic heading by taking into account the
effect upon his aircraft of both wind speed and direction. In order to
do this, he would have ascertained from Pilot Information Service or
the Weather Bureau the wind conditions which prevailed. This done,
he would have used the wind speed and direction factors to
calculate his compass heading, ground speed, time of arrival and
the amount of fuel needed for the flight
You remember that a heading is a course corrected for wind effect.
By drawing a wind triangle (or by using a computer) both the proper
wind correction angle and the ground speed of the aircraft in flight

may be found. It is necessary, however, that the airspeed of the
aircraft, the true course it is to follow, the wind speed, and the wind
direction be known.
If you measure the true course direction from Bowman Field to
Cincinnati-Lunken Airport you will find that its direction is 48°. You
know the speed of your aircraft to be 90 m.p.h. Information concerning
wind conditions discloses that the wind is 8 m.p.h, from 7°. You now
take a plain sheet of paper and draw a vertical line upon it,
representing a north-south direction. Using a scale and a protractor, or
a combination of the two called a plotter, draw a true course line in the
direction of 48°. To do this you place the base of the protractor or of
the protractor portion of the plotter along the vertical line just drawn,
so that the protractor circle faces east; place a dot which you label “O”
at the midpoint of the protractor base and a second dot at 48°. Draw a
line from "O" through the second dot. Now replace the protractor,
keeping the midpoint of the base at "O" and mark a third dot at 7°.
Place your scale so that it intersects this third dot and the dot at "O".
Then draw a line from 7° toward "O". (The wind is from 7°.) Using the
scale or the scale portion of the plotter, measure 8 units along this line
and make a fourth dot. (One unit represents one mile per hour.) Label
this dot "W". Now place the scale on "W" and adjust it so that it
intersects the true course line 90 units from "W". Label this point of
intersection "D'. (See illustration, page 26.)
By placing the mid point of the protractor base at D, you can read the
number of degrees in the angle ODW (4°). This is the wind correction
angle, (WCA), and in this instance, since the wind is from the left, if its
value is subtracted from the true course, the remainder will be the true
heading. The true heading may also be found by extending the line
WD until it intersects the north-south line and measuring its direction.
To measure its direction, place the mid point of the protractor's base at
this point of intersection. You can then read the direction of line WD at
the curve of the protractor. This is your TH.
You will discover it to be 44°.
By measuring the number of units in line OD, you can discover the
ground speed in miles per hour that you will likely make good during
your flight You can estimate arrival time on the basis of this speed.
If you know the rate at which fuel is used by your aircraft engine
(since you already know the time which will elapse during your flight,

can determine its fuel needs. For example, if you know that your engine
burns 6 gallons of fuel each hour, that you have a distance of 240 miles to
fly, and that your ground speed is 80 m.p.h., you can find the amount of fuel
you need.
(Miles per hour

X rate of fuel consumption.

240 miles
X 6 gallons of fuel per hour = 18 gallons of fuel.)

Substituting 80 m.p.h.

Solving the wind triangle problem made it possible to find a true
heading. You know that to fly a true heading, it may be necessary to
fly a compass heading (indicated heading) that may vary
considerably from the true heading. This is because of magnetic
variation and compass deviation. Some pilots use a planning chart
similar to the following, upon which has been assembled the dead
reckoning data needed on your flight:
Pilots' Planning Chart
Cruising Air Speed
TC Speed Direction WCA TH VAR MH D CH From: Bowman Field
Cincinnati-Lunken 48° 8 m.p.h. 7° 4°L 44° 1°E 43° 2° E 41°

Time Fuel Rate Fuel Used 84 m.p.h.
1:05 6 gal/hr 6 1/2 gallons

There are several types of dead reckoning problems that may be
solved by the wind triangle method. For example, a round trip flight
may be graphically represented by extending the line OD in the wind
triangle problem (see illustration, page 26) toward 228° (TC on the
return trip), placing the scale on W and adjusting it so that it intersects
the 228° TC line 90 units from W. By converting the wind triangle

problem into a round trip problem you discover that on the return
trip, you add the 4° WCA to the TC to get the TH, and that your
ground speed is greater than your airspeed (96 m.p.h.).
The wind-triangle problem, solved by the graphic method, is actually
a vector problem. A vector has both force or velocity and direction.
It may be represented by a line. In the simple wind triangle problem,
the magnitude and direction of two vectors (lines) are used to find a
resultant (another line). One vector represents the airspeed and TH
of the aircraft; the other, the speed and direction of the wind; the
resultant represents the TC and ground speed of the aircraft. Had
the values of the resultant and one vector been known, the values
of the other vector could have been found. For example when one
knows the aircraft's airspeed and true heading and its groundspeed
and true course he may find the wind velocity and direction which
affected its flight.
There are a number of special navigation problems based upon the
wind vector diagram (wind triangle) that commercial and air
transport pilots should know how to solve. Sometimes a pilot knows
his true heading (TH), air speed (AS), and wind conditions, but
needs to discover his true course (TC), and ground speed (GS).
Applying the principle of the wind triangle problem makes possible
the prompt solution of this problem.
Sometimes a pilot knows his TC, TH, GS, and AS and wants to
learn the wind direction and velocity. In this instance he simply
supplies the wind vector, measures its length which gives him wind
speed, and its direction which is the same as the wind direction.
Sometimes a pilot has only his air speed and drift angles on two
directions to find the wind velocity and direction. Essentially, the
solution of this problem depends upon the construction of two wind
triangles in combination. The wind vector will be common to both. Its
measurement will give the desired information.
Problems such as these and off course problems are solved by
employing the principle of the vector diagram. Computers provide
one with a convenient way of doing this. However, to acquire skill
and exactness in the use of the graphic diagram or the computer
requires practice. Until such time as you need to use these skills in
practical situations, it is sufficient that you understand in a general
way their method and importance.


The use in navigation of instruments based upon the principles of
radio and electronics is becoming increasingly important. Of the four
types of navigation, radio alone is virtually independent of the
Moreover, modern aviation is coming to depend increasingly upon
the airport and airway facilities based upon recent tremendous
advances in radio invention. (See Airports, Airways, and
Electronics.) However, before an aircraft can take advantage of
some of aviation's electronic aids, it must be properly equipped, and
such equipment is expensive. Yet, the advantages of radio flight so
overshadows such a disadvantage that most of today's aircraft are
provided with a radio receiver-transmitter.
In order to use the four-course radio-range signal for the purposes of
navigation, an aircraft needs to be equipped only with a radio
receiver and antenna. Although this equipment is simple, the
navigational procedure it requires is rather complex. Also, its
operation takes considerable pilot skill and time. More complex
equipment actually requires less operational skill and time.
The four-course radio range in navigation.
You know that it is possible to control the direction of radio waves by
transmitting these from a loop or a rectangular antenna. The strong
signal will emanate from the long sides of the antenna; and virtually
no signal is broadcast in the plane at right angles to the long sides of
the loop. This makes possible the use of two loops, each bisected at

right angle by the other, as a course marking device. One loop
broadcasts an N ( _ . ) signal in one direction; the second broadcasts
an A ( . _ ) signal in the other. The broadcasts are so spaced that in
the areas of least signal strength where the signals overlap no letter
signals can be detected, only a steady "hum" is heard by the pilot.
The pilot can fly this "hum" or "beam" directly to a radio range station.
However, occasions may occur when he gets "off the beam." Under
such circumstances he logically wants to return to his course.
To do this, he must (1) identify the quadrant (one-fourth part of a
circle, in this case one of the two areas into which either the signal A
or N is broadcast); (2) locate the beam; and (3) make sure he is
headed in the proper direction along the beam.
The radio compass.
If an aircraft is equipped with a radio compass (sometimes called a
homing device), its pilot need never be bothered with quadrant
orientation, but must make certain that his plane is headed toward
and not away from the radio station. The radio compass is based
upon the directional characteristics of the loop antenna. When the
loop is at right angles to a station, the signals received are very weak.
The loop antenna of the radio compass is fixed at right angles to the
longitudinal axis of the plane, so that when the plane is headed either
toward or away from the station only weak signals are received and
the indicating needle of the radio compass points to zero.
The radio direction finder.
The radio compass uses a fixed loop antenna; the radio direction
finder uses a rotatable loop. To use the radio direction finder, a pilot
rotates the loop until he gets a null (no signal) through his
Rotating the loop also turns an indicator on the scale of the direction
finder. Consequently, when the pilot gets a null through his
headphones, he can read on this scale the bearing of the station from
his aircraft.
By taking bearings on two separate stations and drawing lines of
position in the direction of the reciprocals of these, he can locate a fix.
The fix is at the intersection of two lines of position plotted on an
aeronautical chart and gives the pilot the position of his aircraft.
It is current practice to use radio navigation instruments in conjunction
with one another and with other more basic navigation instruments. It
is likely, however, that VOR, DME, The Course Line Computer,

Celestial coordinates.
Just as the position of cities are fixed upon the surface of the terrestrial sphere by means of coordinates called meridians of longitude
and parallels of latitude (see page 9), the position of the stars on
the celestial sphere are fixed by means of coordinates. Just as the north
and south pole and the equator of the terrestrial sphere (the earth)
are used as reference points for establishing meridians of longitude
and parallels of latitude, the north and south celestial poles (extensions
of the terrestrial axis) and the celestial equator (extension of the plane
of the terrestrial equator) are used as reference points for the celestial
The celestial coordinates corresponding to the parallels of latitude
on the terrestrial sphere are called parallels of declination and are
m e a s u r e d i n d e g r e e s n o r t h o r s o u t h o f t h e c e l e s t i a l e q u a t o r. T h o s e
corresponding to the meridians of longitude on the earth's surface are
called meridians of the sidereal hour angle (SHA). The SHA is measured
only westward from the prime celestial meridian. The prime celestial
meridian is a great circle passing through the north and south poles
The Radio Fix

and other similar devices eventually will render obsolete some of the
radio navigation devices and techniques now in use. (See, Airports, Airways, and Electronics, pages 32-35.)

Celestial navigation.
As the term celestial navigation implies, the stars in the heavens are
used as points of reference by the navigator. As one looks into the sky
at night, the heavens appear as a hemisphere studded with stars.
The stars are so far away that they all appear fixed and at an equal
distance from the earth. In fact, the navigator must assume that such
is the case, that each star has a definite position on the surface of a
celestial sphere, and that this sphere encloses the earth (the
terrestrial sphere).

and the vernal equinox. The vernal equinox is that point at which the
p l a n e o f t h e e c l i p t i c c r o s s e s t h e c e l e s t i a l e q u a t o r. ( T h i s i s c a l l e d t h e
first point of Aries, the ram; it is symbolized by the sign of the ram's
horns.) The ecliptic is that plane, assumed to pass through the center
of the sun, which contains the orbit of the earth; consequently, it is the
apparent path of the sun.
Celestial Coordinates

If the coordinates of the earth and those of the celestial sphere always
matched each other, each star would always have the same substellar
point on the earth's surface. If this were the case, it would be a
comparatively simple task for a navigator, skilled in the use of the
instruments of celestial navigation, to find his position.
The observer would find the altitude of two stars and draw a circle of
position for each. Or rather, he would draw only segments of these
circles on the chart area which he knows to encompass his generally
known position. The point of intersection of these two lines of position,
under such circumstances, would disclose his position (a fix).
Since the earth is revolving constantly, not only upon its own axis but
also around the sun, the procedures of celestial navigation include
other steps than those outlined above.

T h e P r o b l e m o f Ti m e

Circles of Position

Circles of position.
Each star has, at any given time, some point on the earth's surface
which is directly beneath it. This point is called its substellar point.
At this point the star is said to be at its zenith (directly overhead),
and the angle formed by a line from the star to this point and a line
from this point to the horizon is 90".
When an observer moves away from the substellar point, the angle
formed by a line drawn from his position through the substellar point
toward the horizon, and one from his position drawn toward the star
will be less than 90°. With the substellar point as the center any
number of concentric circles may be drown. At any point on each
circle the altitude of the star (the angle formed by lines from star to
observer's position, to horizon) is the same. Such circles are known
as circles of position.

The problem of time.
Because of these movements of the earth, the celestial navigator
discovers that he must be concerned with both a solar (sun) day
and a sidereal (star) day. Just as the solar day is measured from the
time it takes the sun to leave a point in the heavens and return to
that point, a sidereal day is measured from the time it takes a star to
leave a point in the heavens and return to that point. Because of the
movement of the earth in its orbit, the solar day is longer than the
sidereal day. The difference between the length of solar and
sidereal day affects the daily position of a star's substellar point.

The celestial navigator’s reference sources.
When a navigator knows the position of the Greenwich meridian with
respect to the prime celestial meridian, at the time of his observations,
he can discover the substellar point of the stars in question. In order to
discover this relationship he needs to use information published in the
American Air Almanac1 and a publication of the U. S. Hydrographic
Office, known as Ha 249, published in three volumes. These will
provide data needed to solve problems of celestial navigation.

The celestial navigator’s instruments.
In addition to these indispensable sources of reference, the celestial
navigator must use two instruments without which he cannot locate
his position. One of these is a chronometer (a precise and accurate
timepiece). The other is an instrument which measures the altitude
of a star. As a general rule, marine navigators use a sextant for this
purpose, while aerial navigators use a bubble octant.
Once a basic understanding of celestial navigation is acquired and
the steps of its procedure learned, accurate celestial navigation
depends upon the degree of skill developed by the navigator in the
use of his instruments and books of reference.
The mathematical skills it requires are no more complex than those
required in dead reckoning. Once the terms it employs are
understood, much of its mystery is lost.

Published four limes each year by the U. $. Naval Observatory.
A sextant refers to one-sixth of a circle; an octant to one-eighth of a circle.


Just as the state of the weather is important to men who sail the sea,
it is important to men who follow the paths of flight. For the wind and
weather cause the conditions that complicate the tasks of pilots and
navigators. Many of the rules of air traffic are made necessary because
o f t h e e ff e c t s o f t h e s e . R e s e a r c h a n d d e v e l o p m e n t i n n a v i g a t i o n a i d s
have been stimulated by the need to operate aircraft under all types
of weather conditions. The fact that the force and direction of the wind
are elements of even the most simple problem of air navigation establ i s h e s t h e i m p o r t a n c e o f t h e w e a t h e r f a c t o r.

The atmosphere.
The atmosphere is the great ocean of air which surrounds the earth.
Air, since it is a mixture of gases, has characteristics in common
with other gases. It has weight, exerts pressure, and is
compressible. (See Aircraft in Flight, page 8.) It is subject to the
same gas laws or principles to which other gases are subject. (See
Power for Aircraft, page 8.) The mixture of gases which make up the
air contains 78% nitrogen, 21% oxygen, and 1% several other
gases. These other gases are carbon dioxide, argon, neon, helium,
krypton, xenon, ozone, radon, hydrogen, and water vapor. Some
meteorologists estimate the thickness of the atmosphere to be 600
miles. They think of it as divided into layers. The first layer above the
surface of the earth is called the troposphere. (Troposphere means
region of change. It is in this layer that most weather change takes
The second layer, called the tropopause is a thin layer separating
the troposphere from a third layer, called the stratosphere. Above
the stratosphere lies the ozonosphere, and the ionosphere.
At mid-latitudes the troposphere extends to an elevation of about
35,000 feet. Because air has weight and is compressible, the air at
sea level is heavier than it is at any elevation above sea level. That
is the weight of (the pressure exerted by) the upper atmosphere
compresses the lower atmosphere, reducing its volume. We call this
relationship between weight and volume by the term density. This
relationship can be shown by the formula: Density = weight / volume

We discover that with altitude, both the pressure
exerted by the air (and consequently its density)
and its temperature decrease. Under average
conditions, sea level air has a pressure that will
support a column of mercury (Hg) 29.92" high
and has a temperature of 59°F. At the 5000 foot
elevation, its pressure has fallen to 24.89" Hg;
its temperature to 41.2°F. At the 20,000 foot
elevation, its pressure has fallen to 13.75" Hg;
its temperature to--12.3°F.
The discoveries that the scientists, Boyle and
Charles, made during the 17th and 18th Century
revealed some important things about the nature
of gases. One of the most significant of these
discoveries was that the volume of a body of gas,
its pressure, and its temperature are related.
This means that when one of these essentials
changes, the other two change. For example,
when the temperature of an air mass rises, its
volume increases (consequently its density
decreases). Because of the relationships of these
characteristics, when a mass of air of a given
volume is heated its pressure increases, it
expands, its density decreases, and it is displaced
by surrounding air which is cooler and heavier.
Both vertical movements called convection
currents, and horizontal air movements called
winds take place as a result of these changes.

This behavior, under certain conditions, of the
gases that comprise the atmosphere is responsible not only for the wind but also for other
weather phenomena. We have noted the changes
that take place in gases when temperature
changes take place. Temperature is a function of
heat. Heat also causes the water of the earth's
surface to evaporate (change its state from
liquid to vapor). Warm air can contain a

greater amount of water vapor than cold air. Consequently, when air
containing considerable amounts of water vapor reaches an elevation
where the temperature is comparatively low, it is cooled. Its water
vapor condenses. The condensation products--clouds, fog, rain—
occur. Yet, before the balance of the troposphere is disturbed and
wind and weather conditions happen, a source of heat must affect the
temperature of the air mass and increase its water vapor content.
The sun and the weather.
The sun is the earth's great source of energy. Not only does the
weather but also all life and all life-activity upon the earth depend
upon the energy from the sun. The heat from the sun is transferred to
the earth by means of radiant waves.
The methods of heat transfer.
There are three principal ways in which heat is transferred from one
place to another. These ore called conduction, convection, and
radiation. Conduction is the transfer of heat between objects whose
surfaces are in contact one with the other. Convection is the transfer
of heat in liquids or gases by means of currents within the liquids or
Radiation is the transfer of heat by means of radiant waves.
The heat energy of the sun reaches the earth through radiation. This
method transfers heat energy without changing the temperature of
anything between the source of energy and the object heated. Heat
energy escapes o generating source in the form of waves. These
radiant waves (or rays) are themselves a form of energy. When
radiant energy from one object reaches another object it changes
again into heat energy.
Scientists classify radiant waves according to their length. Radiant
waves of different lengths ore assumed to form a band, or spectrum.
At one end of this band are the shortest waves. At the other end the
longest waves. Waves sent out by the sun include the ultraviolet rays,
visible light rays, and infrared waves. Ultraviolet rays are invisible
rays that lie beyond the violet rays toward the short-wave end of the
spectrum. Infrared rays are invisible rays that lie beyond the red rays
toward the long-wave end of the spectrum. The visible light rays lie
between the ultra violet and the infrared rays. The waves of any of

groups are not of identical length. For example, there are short infrared
waves and long infrared waves depending upon the distance of the wave
from the visible red of the spectrum.
Radiant energy is never destroyed although only about 43% of the sun's
radiation toward the earth ever reaches its destination. Radiant waves
may be absorbed and reflected by clouds in the atmosphere; they may be
scattered and reflected by dust in the atmosphere; they may be
transmitted through the atmosphere; they may be absorbed by the earth
and converted into heat and long-wave infrared rays. During the
processes by which water from the earth's surface evaporates into the
atmosphere, much heat (radiant energy) is absorbed. It takes 590 calories
to change one gram of water into water vapor. And although it causes no
increase in the temperature of the water vapor which results, no heat is
lost. When the water vapor later condenses, heat is released and does
affect the temperature of the surrounding air. This is a point to be
remembered, since the heat thus released helps generate thunderstorms
and the winds and violent air currents which accompany them.
The rate at which the earth's surface is heated is called insolation.
Changes occur in insolation as changes occur in the angle (the angle of
incidence) that the sun's rays make with the horizon, changes in the
distance of the earth from the sun at any given time, and changes in the
amount of radiation absorbed by the atmosphere. On clear days more
radiation reaches the earth's surface than on cloudy days. Very dense
cloud formations may reflect as much as three-fourths of the radiant
energy from the sun.

Angles of Incidence Insolation is greater at the equator than
elsewhere on the earth's surface because, at the equator, the
angle of incidence is greater.
(The sun's rays are more nearly perpendicular.) Consequently,
more radiant waves per equal area (hence, more heat) reach the
equatorial zone than reach the temperate zones, and more reach
the temperate zones that reach the polar zones. (See illustration
above.) In January the earth is about 3,000,000 miles nearer the
sun than it is in July. If the axis of the earth were not tilted in
relation to its orbit (23.5°), January in the Northern Hemisphere
would be warmer than July. The greater angle of incidence in July
over January accounts for summer in the Northern Hemisphere.
Seasons, of course are reversed for the Southern Hemisphere.
During the summer season there, the earth is comparatively
nearer the sun and the summers of the Southern Hemisphere are
comparatively warmer than those of the Northern Hemisphere.
The Heat Balance

The heat balance.
Were there not a balance of heat between the earth, its atmosphere
and space, the earth--bombarded continuously by radiant waves—
would become increasingly warmer. This does not happen because the
radiant energy received by the earth is in turn radiated from the earth
into space or transferred by another means into the atmosphere.
Students of meteorology have estimated that of all the solar radiation
toward the earth: 42% is reflected into space by clouds and
atmospheric dust and 15% is absorbed directly into the atmosphere;
43% reaches the earth; 39% is subsequently absorbed by the
atmosphere after it reaches the earth's surface; 4% is again returned
from the atmosphere to the earth by means of convection; 8% is
radiated by the earth and transmitted through the atmosphere directly
into space.
The processes which tend to maintain the heat balance are chiefly
responsible for weather changes.
The wind.
You have learned that insolation (the rate of heating of the earth's
surface) is greater in the equatorial zone than it is within the temperate
and polar zones. For this reason, the temperature of air in contact with
the earth's surface within the equatorial zone rises more rapidly than
does the temperature of air in contact with the earth's surface within
temperate and polar zones. If the earth did not rotate, the result would
establish a gigantic convection. The increase of surface air temperature
would cause an increase of the air volume and the air pressure (see
page 39); the upper air would move from the equator toward the poles;
surface air would move from the poles toward the equator.
However, the earth does rotate and irregularities characterize its
surface. Consequently, the system of the winds is somewhat complex.
Air movements on a Static and Rotating Sphere

Isobars on a weather map
indicate degrees of pressure
within a high.

Representation of
flow of air aroud s

The pressure gradient

As a result of the earth's rotation, the nature of air currents generated
within the equatorial zone is modified by a factor called the coriolis
force. In the Northern Hemisphere this force tends to deflect the wind
to the right of its path. Consequently, as the heated air above the
equatorial zone rises and moves northward, it tends to change its
direction toward the east. By the time it reaches Lot. 30°N. it is
blowing directly eastward and causes an accumulation of air and a
high pressure belt at this latitude.
As the air pressure builds up within this belt, some of the air is forced
downward toward the earth's surface. A portion of this flows back
Wind systems

toward the equator along the surface; another portion flows toward the
poles along the surface.
Meanwhile, some of the air aloft continues to flow toward the poles,
becomes cooled, settles to the surface and begins a return trip to the
equator. The warmer surface air moving up from latitude 30° overruns
this colder air and, continuing northward, produces a high pressure
condition in the polar zones. At irregular intervals when the pressure
becomes sufficient, massive air waves break out of the polar zones.
These waves moving toward the equator cause the changeable
weather conditions which are characteristic of the middle latitudes.
The pressure gradient and its effects upon the wind
The irregular distribution of oceans and continents, seasonal changes,
and daily temperature variations, are among the different influences
which cause the atmosphere to assume the nature of a constantly
changing landscape made up of invisible mountains and valleys. The
high-pressure areas of the atmosphere are the mountains; the lowpressure areas, the valleys. The wind flows from these high pressure
mountains into the low pressure valleys, just as great streams of water
might flow from on actual mountain into a valley below.
The slope of the high pressure mountain is called the pressure
gradient. On weather maps, its degree of steepness is shown by lines,
similar to contour lines (see page 44), called isobars. Isobars are
drawn through points of equal sea-level atmospheric pressure.
The effects of gravity and friction upon the wind.
Still other factors which affect the circulation of the air are gravity,
friction, and centrifugal force. Gravity tends to pull the air downward,
and produce a graduated, air-density distribution, with the greatest airdensity near the earth's surface. Friction tends to retard air movement;
it is effective to an altitude of 1500 to 2000 feet above the ground.
Centrifugal force acts on air moving in a curved path so as to decrease
its speed within a low pressure area and increase it within a high
pressure area. In the Northern Hemisphere the air flows clockwise
1 Weather maps express atmospheric pressure in terms of millibars. A
millibar is a unit of pressure equal Is o force of 1000 dynes per square
centimeter. A dyne is a force which applied to a mass of one gram for
one second will give it a velocity of one centimeter. Standard sea-level
atmospheric pressure is 1013 millibars. Atmospheric pressure may
also be expressed in lbs./sq. in. or inches of mercury (Hg.).
2 The actual atmospheric pressure of o reporting station converted to
that which would prevail were the station located at sea level.

around a high pressure area (an anticyclone) and counter-clockwise
around a low pressure area (a cyclone).
It should be noted that at an altitude where surface friction ceases to
affect wind movement, the wind always blows parallel to the isobars.
At this level, called the gradient level, the pressure gradient force
balances the coriolus force. The wind at this level is called the
gradient wind. Its speed is always inversely proportional to the
distance between the isobars. This means that when the isobars are
far apart, the wind is weak; when they are close together, the wind is
strong. Pilots of long distance flights always try to take advantage of
favorable winds and plan and navigate their flights accordingly.
Local air movements.
The general circulation of the air is complicated by the irregular
distribution of land and water areas. Different types of surfaces differ
in the rate at which they transfer heat to the atmosphere. Seasonal
changes and daily variations in temperature also affect this rate of
transfer. In some regions, local low pressure areas form over hot
land surfaces in summer and over the warmer water surfaces in
winter. Along shore lines convection currents are formed which
during the clay cause the wind to blow from water over the land and
during the night to flow from the land over the water.
Local air circulation of limited scope is caused by the variations in
the earth's surface. Some surfaces such as sand, rocks, and barren
land give off a great amount of heat. Others, such as meadows,
cultivated fields, and water, tend to retain heat. Rising air currents
are encountered by an aircraft in flight over the one type of surface,
descending air currents are encountered over the other.
Moving air flowing around obstructions tends to break into eddies.
On the leeward (opposite the windward) side of mountains there are
descending wind currents. Such local conditions cause turbulent air.
A pilot flying into the wind toward mountainous terrain will place
enough distance between his aircraft and the mountain top to avoid
dangerous, descending air currents. Light plane pilots sometimes
approach mountains at a 45° angle so they can turn back in a short
period of time if turbulence is encountered.
The jet stream.
A jet stream is a comparatively narrow current of air which moves
around either the north or south hemispheres of the earth at speeds

from 100 to 250 miles per hour. It moves from west to east at an
altitude of approximately 30,000 feet.
Air speeds increase toward the core of the stream. An aircraft
climbing or descending through a jet stream may encounter
differences in wind speeds of 30 miles an hour per 1000 feet of
altitude change.
A difference in wind speed of 100 miles per hour between the outer
edge and the core of the stream is not unusual. Also, differences in
wind speeds up to 100 miles per hour between regions of maximum
and minimum wind speed along the core of the jet stream may be
The jet stream shifts position frequently and actually migrates with
the seasons. Sometimes two streams flow across the United States,
the one along the northern border and the other well toward the
The cruising range of an aircraft flying downwind within a jet stream
is greatly increased. However, flying against a jet stream limits the
cruising range and such flight operation should be avoided.
Consequently, pilots anticipating high altitude or long range flights
attempt to discover the location of the jet stream.
Water vapor enters the air when the surface water absorbs enough
solar radiation in the form of infrared rays (see page 41) to change its
state from liquid to gaseous. Under average circumstances the
atmosphere contains 12 parts of water vapor to 1,000 parts of air.
Water may be found in the atmosphere in any one of its three forms:
solid, liquid, or gaseous. However, it is in the form of gas (vapor) that
water is first mixed with air. The other forms result when water vapor
The term, dry air, characterizes air that contains no water vapor.
The term, humid air, characterizes air that contains water vapor.
When a parcel of air can contain no more water vapor, it is said to be
saturated. The amount of water vapor which the air can contain
depends upon the air temperature. The ratio of the amount of water
vapor which a sample of air holds to the amount it can hold when
saturated is called relative humidity.
When the relative humidity of a parcel of air is 100%, it becomes
saturated. Should the temperature of such a body of air be reduced,

some of the water vapor it contains would become liquid. Moreover,
the heat used to change its state from liquid to gas, as a result of
such condensation, would be released into the atmosphere.
Before condensation can take place, the atmosphere must contain
condensation nuclei. Large quantities of these are generally present
in the form of tiny particles of dust and minute products of
The products of condensation include clouds, rain, drizzle, hail, dew,
freezing rain, freezing drizzle, snow, frost, and sleet. Before any form
of precipitation can occur, even after the air reaches its saturation
point, clouds must form and water droplets must be super-cooled
(reach a temperature below freezing).
Both the temperature and the pressure of the air decrease with an
increase of altitude. Perfectly dry air decreases in temperature at the
rate of about 5 1/2°F. per each 1,000 feet of elevation (dry adiabatic
lapse rate); under average humidity conditions air temperature
decreases at about 3 1/2 °F. per each 1,000 feet of elevation (normal
adiabatic lapse rate). The rate of temperature decrease with altitude
for moist air depends upon its relative humidity.
As a parcel of air ascends and gains altitude it experiences lowering
pressures. Consequently, it expands. When a gas expands, work is
done and heat energy is converted into mechanical energy. As a
parcel of air descends, it is subject to increasing pressure, the
process of energy change is reversed, and the temperature of the air
is increased. When no heat is added to such a parcel of air, any
expansion or compression which brings about a temperature change
is called an adiabatic process. If the expansion or compression of an
air parcel results from heat added to or taken from it, the process is
Both the isothermal process and the adiabatic process are important
factors in weather changes. It appears that the isothermal process
initiates both the air mass movements and the local convection
These air movements and currents cause the lifting of air parcels.
Condensation results when ascending air is affected by the adiabatic
process. Release of the latent heat of condensation adds heat to the
air; consequently the isothermal process again takes place. The
violent air currents which characterize thunderstorms are caused in
part by the expansion of the air which takes place when additional
heat energy becomes available.

Local air circulation, daytime

Local air circulation, at night
Te m p e r a t u r e c l a s s i fi c a t i o n o f a i r m a s s e s .

Although clouds and fog may form because of conditions and procedures within an air mass, general weather changes are the result of
t h e m e e t i n g o f a i r m a s s e s h a v i n g d i ff e r e n t c h a r a c t e r i s t i c s . A i r m a s s
characteristics parallel those of the area in which the air mass originates.
A polar air mass (P) is cold; a tropical air mass (T) is hot; a maritime
air mass (m) is humid; a continental air mass (c) is dry.
As an air mass moves away from its source of origin its original
characteristics are changed because of the nature of the earth's surface
over which it passes. It may become warmer or colder; absorb moisture
or lose moisture; be lifted by mountains or subside into valleys. However, an air mass is not likely to lose all of its original characteristics

The temperature classification of an air mass is based upon its temperature in relation to the surface over which it passes. As an air mass
moves from one surface to another it could change from a cold air mass
(k) to a warm air mass (w), or from a warm air mass to a cold air mass.
On weather maps an air mass is identified by letter symbols. An air
mass originating in the polar zone and moving toward the south over
a comparatively warm surface will be identified on a weather map by
the symbol cPk. An air mass originating over the Gulf of Mexico and
moving toward the north over a comparatively cold surface will be
identified by the symbol mTw.
Characteristics of air masses.
The characteristics of an air mass depend upon the seasons, its
distance from its source of origin and the position of the observer in
relation to the frontal zone of the air mass (front). In general, a cold
air mass is characterized by cumulus and cumulonimbus clouds (see
illustration, page 53), by local thunderstorms, showers, hail, sleet, or

The Warm Front

snow flurries. Pronounced turbulence exists in its lower levels; yet,
except during precipitation, the cloud ceiling is usually unlimited and
visibility conditions are good. On the other hand, a warm air mass is
characterized by haze, fog, stratus clouds, and drizzle. Warm air
masses have little or no turbulence; yet, visibility conditions are poor
and cloud ceilings generally low.
The general movement of the atmosphere across continental United
States is toward the east. Air masses originating in the tropical and
equatorial areas move toward the northeast. Those originating in the
Arctic and Polar areas move toward the southeast. Cold air masses
move more rapidly than warm air masses. The speed of an air mass
may average from 500 to 700 miles in a day, depending upon its
nature and the season of the year.
The boundaries set up between one another by air masses of different
characteristics are called frontal zones or fronts. This boundary or
front moves along the earth's surface as one air mass tends to displace
a n o t h e r. I f a c o l d a i r m a s s t e n d s t o r e p l a c e a w a r m e r a i r m a s s , t h e
boundary is called a cold front; if a warm air mass tends to replace

The Cold Front
a cold air mass the boundary is called a warm front. When there
is a marked temperature and humidity difference between the
two air masses, weather changes along a front are pronounced.
The cold front.
Cold air is denser and heavier than warm air. Because of this
fact, the warm air lying ahead of a moving cold front is lifted, and
its temperature is lowered. The result is a belt of frontal activity
(a squall line) 50 to 100 miles wide which may extend for
hundreds of miles in length. In the United States such fronts
extend from southwest to northeast.
The cold front has a steeply curved slope. Its progress is more
rapid than a warm front. If its movement is comparatively slow,
nimbostratus clouds are formed at the front. If its movement is
comparatively rapid, cumulonimbus clouds will form and heavy
precipitation and turbulent winds will occur.
A cold front causes a complete change of weather within the
space of a few hours. After a cold front passes, the wind
direction will change, the weather will clear, and the air will
become cooler and drier.

The warm front.
A moving warm front overrides the cold air ahead of it, forming a
wedge like segment of cold air directly below its slope. This slope is
comparatively gradual. It rises about 1,000 feet for every 20 miles. It
may extend for several hundred miles. As the warm air moves up the
slope and its temperature falls, condensation occurs. Fog and drizzle
first occur; low nimbostratus clouds then form, and the drizzle turns
into rain; at increasing heights along the slope stratus, altostratus, and
cirrostratus clouds form. Wisps of cirrus clouds may lie on a warm
front slope at an altitude of 20,000 feet and 400 or more miles ahead
of the intersection of the frontal slope with the earth's surface. Unlike
the cold front, the warm front signals the weather changes it is to
bring. Just as a change in wind direction takes place after a cold front
passes, so does a wind shift take place after a warm front passes.
The occluded front.
The development of occluded fronts is associated with the
development of low pressure areas. Under certain conditions there is
a tendency for a wave motion to occur along a front This wave is not
vertical like an ocean wave, but is horizontal. After the frontal "bend"
starts it takes three or four days for the process to be completed. A
second stage occurs as the cold air begins to surround the warm air.
The warm air, rapidly lifted, cools and severe precipitation occurs The
final stage is reached when the warm air is completely surrounded.
The air pressure then becomes less at the wave than at other points
within the surrounding areas, the frontal surfaces tend to whirl
together, and a "low" has been created.
As the occluded front approaches, one may observe warm front
weather characteristics. Lowering cloud ceilings, lowering visibility,
and increasing precipitation takes place in the order stated. Following
the warm front weather, cold front type weather occurs--squalls,
thunderstorms, and turbulence.
Clouds are sometimes called the signposts of the weather. There are
two general types under which all clouds can be classified. These
types are cumulus and stratus. (See illustration, pages 52 & 53.)
Cumulus clouds appear to be piled one on top of another. They are
formed by vertical currents. Stratus clouds are spread out in layers.
Clouds near the earth's surface are designated as either cumulus or

The weather sequence report
stratus unless they are producing precipitation. When they are
producing precipitation, the term nimbo is added either as a prefix
(nimbostratus) or as a suffix (cumulonimbus). The term alto is added
to cumulus or stratus to identify such types when they lie between
5,000 and 20,000 feet. The term fracto is prefixed to the names of
the general types when clouds appear broken. Clouds between
20,000 feet and 50,000 feet are composed of ice crystals, have a
characteristic curly appearance, and are called cirrus clouds. The
term cirro prefixed to cumulus or stratus identifies the different types
of cirrus clouds.
It is quite easy to remember the names of the clouds. Simply learn
the names of the two basic types: cumulus and stratus. Then
remember the meaning of the terms combined with these names:
nimbus means rain; alto means high; fracto means broken; cirrus
means curly.
The weather elements.
In order to gather weather information and to report this to
forecasting centers so that future weather can be predicted, ten
weather characteristics are measured. These conditions are (1) sky
cover, (2) cloud ceiling, (3) visibility, (4) state of the weather, (5)
pressure, (6) temperature, (7) dewpoint (humidity), (8) wind
direction, (9) wind velocity, and (10) precipitation. The variations of
three of these elements can be measured only by the eye (visually);
variations of the others are measured by instruments.
Symbols are used to report weather conditions. Weather maps or
charts use one set of symbols. Weather reports use another. The
chart symbols which disclose weather information are clustered
around the reporting station. Such a cluster of symbols is called the
station report. The illustration below (see page 57) shows the
conventional position of each symbol in a station report. You will
note that the

number of feathers and half feathers at one end of the arrow in this
illustration indicates the strength of the wind. The compass direction
from which the wind is blowing is indicated by the position of the
arrow. You will note that the circular symbol at the other end of the
wind arrow indicates the amount of sky cover. To report "state-ofthe-weather" under differing circumstances requires over one
hundred symbols. Six of these are of more importance than the
others, either because they are the basis of other symbols or
because they reveal hazardous weather conditions. (See illustration,
page 57.) Although weather maps are of primary importance as
tools for the meteorologist, they are also important to the pilot. From
them the latter can obtain information about high and low pressure
areas and the position and nature of fronts and squall lines at the
time of observation. From the map he can discover the general
weather conditions along and near the route he plans to fly.
However, it is from weather sequence* reports and forecasts (area,
terminal, or winds aloft) that the pilot obtains specific weather
Weather maps are drawn from observations made at six-hour
intervals beginning each day at 0130 Eastern Standard Time.
Aviation weather reports are made at hourly intervals, at 30 minutes
past the hour. Weather reports and forecasts are transmitted by
teletype. Hundreds of these are transmitted each hour. They must
be both complete and concise. In order to assure these qualities and
to expedite their transmission, symbols and abbreviations are used
to convey weather information.
A group of teletype weather reports will be prefaced by
abbreviations indicating the nature and time of the reports, for
example FCST 05E-17E (Forecast 5 A.M. to 5 P.M. Eastern
Standard Time). Each report of the group will be introduced by the
name (abbreviated) of the reporting station. If a significant change in
the weather has occurred since the previous report was made, the
letter S followed by a number will be the second item of the report.
The S indicates a "special report"; the number is the number of the
special reports made during the reporting day. The other items
correspond in the order of their arrangement to the order in which
the weather elements are generally listed. (See above, page 55.) In
addition, the report contains the proper altimeter setting and
pertinent remarks. The illustration above (see page 55) provides a
key to the interpretation of aviation weather reports.
Each related to the preceding.

The Station report

Area and terminal forecasts make use of some of the symbols used in
weather reports. They also use certain other symbols. One of the
charts displayed at weather stations~ tells pilots how to interpret the
symbols of a forecast (see illustration above }.
As a student of general aviation you should learn the few basic
symbols used in weather reporting. To do this will help you learn
specific symbols readily, should you at some later time wish tO
become skilled in map reading and weather report interpretation. For
the present it is important only that you understand the purpose and
general method of weather reporting.
The weather hazards to aviation.
A principal weather hazard to aircraft in flight is the thunderstorm.
Turbulence, high winds, heavy rain, lightning, and sometimes hail
characterize thunderstorms. A thunderstorm has three stages: (1) the
cumulus stage, (2) the mature stage, and (3) the dissipating stage.
The thunderstorm develops during the cumulus stage. This stage is
characterized by updrafts. They may extend from the surface to an
altitude of 25,000 feet, and they may have vertical speeds up to 30
miles per hour. When rain begins to fall, the thunderstorm has
reached the mature stage. During this stage there are both updrafts
and downdrafts. Updrafts are sometimes strong enough to carry liquid
water to a height where hail will form. Great turbulence takes place
within the thunderstorm. As the thunderstorm nears the dissipating
stage the

downdraft area increases in size. After this stage is reached the
thunderstorm contains only downdrafts, the rainfall gradually decreases,
and the thunderstorm activity stops.
Thunderstorms may be single or multi-cell. A single cell thunderstorm is
rare. Its life cycle is completed in about one hour and fifteen minutes.
Multi-cell thunderstorms may contain cells in various stages of
development and may remain active over a period of hours. Under no
circumstance should pilots of small aircraft attempt to fly through
The formation of ice on aircraft may become a hazard to safe flight.
This is the case when an aircraft is not equipped with means for
disposing of ice formation on the propeller and the wings. Before ice
can form on an aircraft, the aircraft must be flying through moisture that
is visible, such as clouds, rain, drizzle, or wet snow. (Carburetor icing,
you remember, can take place when there is only water vapor present in
the air.) Icing generally occurs when the temperature is between 32°F.
and 20°F. However, it may occur when the temperature is lower than
20°F. Consequently, a pilot who wishes to avoid ice will stay clear of
clouds or precipitation areas when the temperature is below freezing.
Low visibility conditions may also cause hazardous flying conditions.
These conditions result from haze, smoke, fog, snow, low clouds, or
other obstructions to a pilot's vision. Ceiling and visibility are two
weather elements that every pilot carefully considers before undertaking
a flight. These two factors help determine whether the flight can be
made VFR or whether an IFR flight clearance must be obtained from Air
Traffic Control (see Airports, Airways, and Electronics, page 46).

The Thunderstorm

Navigation was first practiced by those who operated ships at sea.
After the airplane was invented and aircraft came into practical use,
the principles of navigation were borrowed from the seafarer by the
aircraft pilot. For, the problems of keeping an aircraft on course and
those of keeping ships on course are solved by the use of similar
methods. Navigation is both a science and an art. It is a science in
that it employs well-established principles and recognizes proven
procedures. It is an art in that it requires from the one who practices
it an adaptability to an ever changing situation. This is because the
navigator must always take into account such variable factors as
wind and weather.
Of first importance to the flight navigator is the aeronautical chart.
His basic navigation instruments are his watch, an airspeed
indicator, a magnetic compass, and an altimeter. By means of the
meridians of longitude and the parallels of latitude, the coordinates
of his chart, he locates his position. By means of the proper
meridian and a protractor, he finds the course which he must make
good to reach his destination. By use of his watch and check-points
he can check his ground speed and estimate his arrival time. His
compass indicates a heading; his airspeed indicator gives the
approximate speed of his craft through the air; and his altimeter
shows the approximate height of his craft above the ground.
Whatever the type of navigation he practices, the pilot finds the
basic navigation instruments indispensable.
The types of navigation are piloting, dead reckoning, radio flight,
and celestial navigation. Charts are made use of in every type of
navigation. Piloting and dead reckoning are used to navigate shortdistance flights. It is the general practice for a pilot to use a
combination of navigation types. Radio flight requires complex
equipment; but it makes the task of the navigator simple.
The magnetic compass does not indicate a true course. The
attraction of the magnetic pole causes the compass needle to vary,
depending upon the region of an aircraft's flight. Some of the metals
used in an aircraft's construction and the electrical instruments with
which it is

equipped may cause deviations of the compass needle regardless of
the region of an aircraft's flight. These facts must be considered in
calculating a compass course.
The direction and speed of the wind are factors which a pilot must
consider when he needs to find the compass heading which will enable
him to make good the desired true course. Wind and weather create
many operating problems that pilots and navigators encounter.
A principal source of energy on earth is the sun. The method by
which it is transmitted to the earth is called radiation. After reaching
the earth, radiant energy changes to heat energy. Heat energy raises
the temperature of the air, increasing its pressure and its volume, and
establishes convection currents. Because of the difference in insolation
between the tropic zone and the temperate and polar zones, general
air movements are initiated. A force created by the rotation of the
earth, called the coriolus force, deflects these movements and helps
cause the winds.
Air masses, their characteristics, and the weather activity which
takes place when different air masses come into contact one with
another are important in the operation of aircraft. The characteristics
of an air mass are determined by the nature of the earth's surface over
which it originates and over which it passes. An air mass is hot or cold,
dry or moist, depending upon whether or not such surfaces are hot or
cold, dry or moist. Frontal activity occurs when moist warm air is lifted
by colder air. Air cooling adiabatically loses its water vapor content
through condensation. Condensation releases the heat employed to
evaporate the water originally. The release of heat contributes to
atmospheric turbulence and to further atmospheric changes.
The types of fronts can be identified by the clouds that precede
them. Pilots should learn the meaning of these signposts of the weather.
In this way many hazards to safe navigation such as icing and low
visibility conditions and thunderstorms may be avoided. The practice
of navigation requires knowledge and skill on the part of pilot and
navigator. It also requires the exercise of good judgment. This is particularly true in the case of the light plane pilot. His flight must be
planned carefully. A most important part of that planning requires that
the pilot learn about the wind and weather conditions likely to prevail
at the time of his flight, and that he navigate his aircraft with this
information in mind.

Mervin K. Strickler, Jr.
Director of Aviation Education
Charles W. Webb
Assistant Director of Aviation
Education Harold E. Mehrens
Chief, Editorial and Curriculum
Division William E. Rowland
Chief, Audio Visual Training Aids


Everet E. Collins, North Central
Region S. Edward Corbin, Great
Lakes Region Monroe L. Hatch.
Middle East Region Arthur I. Marlin,
Southwestern Region Victor E.
Moore. Northeastern Region John
M. Ogle. Rocky Mountain Region
John E, Sims, Southeastern Region
John V. Sorenson, Pacific Region


Emmett A. Betts
Director, Betts Readinq Clinic Willis C.
Specialist for Aviation Education Division of
State and Local School Systems Office of
Leslie A. Bryan
Director. Institute of Aviation
University of Illnols
John H. Furbay
Air World Education
Trans World Airlines, Inc.
George N. Gardner
Superintendent, Educational Services Pan
American World Airways System John L.
Associate Professor
University of California
Department of Business Administration
Philip S. Hopkins
Department Head
Norwich University
Dawson C. McDowell
Director, Institute of Tropical Meteorology
University of Puerto Rico
Merlyn McLauqhlin, Lt. Col., U~AF 58
Gruber Street
Des Haines, Iowa
Raymond O. Mertes
Director, School and College Service United
Air Lines

Kenneth E. Newland
Occupations Division
Stephens College
Willoughby E. Sams, Consultant Aviation
California State Department of Education
Harry C. Schmid
State Director
Vocational Division
Department of Education
Stdle of Minnesota
Frank E. Sorenson
Professor of Education
Teachers College
The Universily of Nebraska
Roland Ft. Spauldinq
Professor in Education in Charge of
Aeronautical Education New York
School of Education
Parker Van Zandt
International Staff. NATO
USRO Defense I
Paul A. Wilkinson
Denver Public Schools
Harry Zaritsky
AudioVisual Division
Naval Medical School
National Naval Medical Center
Jordan L. Larson
Superintendent of Schools
Mount Vernon, New York


Frank W. Hansley, Colonel. USAF Deputy Chief
of Staff, Operations
and Training
Walter W, Thompson, Lieutenant Colonel, USAF
Executive Officer to the Deputy Chief of Staff.
Operations and Training
Marlin R. Walsh, Jr., Lieutenant Colonel. USAF
Director of Operations
Alva L Conner, Lieutenant Colonel, USAF Chief,
Sen~or Operations

Seymour E. I athan~. Mc~io,. USAF
Olrecl(,r o[ rrahlillq
E v a r l c e C . M i r e . J r. . M a i o r. U S A F
Chief ol Senior Tfaininq
J o h n W. S c o t , C ~ l p l a l n , U S A F
Director of Communications
Jock A. Walbert
C o m m u n i c a t i o n s Te c h n i c i a n