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WAR DEPARTMENT
AIR CORPS
FIELD MANUAL
AIR NAVIGATION
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FM 1-30
AIR CORPS
FIELD MANUAL
AIR NAVIGATION
Prepared under direction of the
Chief of the Air Corps
UNITED STATES
GOVERNMENT PRINTING OFFICE
WASHINGTON : 1940
For sale by the Superintendent of Documents. Washington, D. C.- Price 15 cents
WAR DEPARTMENT,
Washington, August 30 , 1940.
FM 1-30, Air Corps Field Manual, Air Navigation, is pub-
lished for the information and guidance of all concerned.
[A. G. 062.11 (5-28—40) .]
By order of the Secretary of War:
G. C. MARSHALL,
Chief of Staff.
Official :
E. S. ADAMS,
Major General,
The Adjutant General.
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TABLE OF CONTENTS
Paragraph Page
Chapter 1. General 1-6 1
Chapter 2. Pilotage and Dead Reckoning.
Section I. General 7-9 3
II. Pilot-navigator 10-14 3
III. Navigator 15-19 6
Chapter 3. Radio Navigation.
Section I. Facilities and equipment 20-26 14
II. Practice 27-30 18
Chapter 4. Celestial Navigation.
Section I. General 31-33 22
II. Instruments and equipment 34r-39 22
III. Celestial line of position 40-47 23
IV. Preflight preparation 48-50 30
V. Practice 51-59 30
Appendix. Glossary of Terms 35
Index 39
III
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FM 1-30
AIR CORPS FIELD MANUAL
AIR NAVIGATION
CHAPTER 1
GENERAL
■ 1. Scope. — This manual is a general treatise on all methods
and technique of air navigation and a brief summary of
instruments and equipment used.
■ 2. Definition. — Air navigation is the art of determining
geographical position and maintaining desired direction of
aircraft relative to the earth’s surface by means of pilotage,
dead reckoning, celestial observations, or radio aids.
■ 3. Employment. — The four means of air navigation are
complementary and are used separately or in conjunction
with each other in military operations. Radio silence, ex-
tremely low ceilings, strange or mountainous terrain, com-
plete overcast, darkness, or necessity for overwater flying are
conditions that necessitate use of one or more of the four
types of navigation.
■ 4. Necessity of Training. — a . The varied characteristics
of military operations tax to the extreme the ingenuity and
ability of those responsible for navigation and require that
personnel concerned be highly trained. It is imperative that
those charged with the responsibility of navigation be well
versed in, and fully competent to use, any and all of the
four navigation methods.
b. Precise flying, both instrument and noninstrument, is
an indispensable requirement of accurate air navigation.
The automatic pilot is capable of more accurate flying than
can be secured by manual piloting and its use improves the
accuracy of air navigation.
■ 5. Instrument Responsibility. — The success of a naviga-
tion mission depends to a great extent upon satisfactory
functioning of the instruments involved, and presupposes
their correct installation, calibration, and operation. The
navigator is responsible for their satisfactory functioning.
He must be familiar with their calibration and operation, and
must be able to use properly their indications in the practice
of air navigation.
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AIR CORPS FIELD MANUAL
■ 6. References. — a. Technical publications. — For a com-
plete list of War Department technical publications, see
FM 21-6.
(1) Technical Manuals. — TM 1-205 and TM 1-206 are
complementary manuals explaining in detail the methods
and technique of air navigation.
(2) Technical orders. — For a complete list of Air Corps
Technical Orders, see Air Corps Technical Order 00-1. Tech-
nical orders set forth information and instructions relative
to specific items of equipment. They are guides for training
personnel in installation, calibration, and operation of par-
ticular items of equipment. In general those covering navi-
gation instruments and equipment fall within the Air Corps
Technical Order 05-series. Radio equipment and facilities
used as aids to navigation are described in Air Corps Tech-
nical Order 08-15-1 and Air Corps Technical Order 08-15-2.
b. Miscellaneous. — (1) Air Corps circulars. — Air Corps Cir-
cular 15-21 contains a list of forms and tables for air naviga-
tion. Air Corps Circular 50-3 contains instructions for altime-
ter setting. Air Corps Circular 65-101 lists the equipment con-
tained in the dead reckoning navigation case. Air Corps Cir-
cular 100-20 contains a description of the Army Airways
Communication System facilities used by the navigator. Air
Corps Circular 90-series contains other aids to navigation.
(2) Hydrographic Office, U. S. Navy. — Navigation tables
and equipment used by the navigator are listed in the General
Catalog of Mariners’ and Aviators’ Charts and Books. The
following publications are of especial interest to the air
navigator:
(a) Useful tables from the American Practical Navigator,
Hydrographic Office 9, Part II.
(b) Radio Aids to Navigation, Hydrographic Office 205.
(c) Dead Reckoning Altitude and Azimuth Tables, Hydro-
graphic Office 211.
(d) Computed Altitude and Azimuth Curves, Hydrographic
Office 214.
(e) Rude Star Finder and Identifier, Hydrographic Office
2102a.
2
'I
CHAPTER 2
PILOTAGE AND DEAD RECKONING
Paragraphs
Section I. General 7-0
II. Pilot -navigator 10-14
III. Navigator 15-19
Section I
GENERAL
■ 7. Pilotage. — Pilotage is the method of conducting air-
craft from one point to another by observation of landmarks
either previously known or recognized from a map.
■ 8. Dead Reckoning. — Dead reckoning is the method of de-
termining geographical position of aircraft by applying track
and ground speed as estimated or calculated over a certain
period of time from point of departure or from last-known
position.
■ 9. Method of Treatment. — Methods of pilotage and dead
reckoning have been treated as a combined method of air
navigation in this manual. However, the combined methoc
has been separated into two divisions, methods and techniqui
of the pilot-navigator limited in equipment and facilities, anc
the more precise methods and technique of the navigator.
Section II
PILOT-NAVIGATOR
■ 10. General. — a. Navigation duties fall upon the pilot in
single place or multiplace aircraft where space or equipment
does not permit or where nature of mission does not require
a navigator. A pilot-navigator seldom employs celestial navi-
gation. Radio navigation will be discussed separately as ap-
plicable only when radio facilities exist.
b. Instruments and equipment available to the pilot-navi-
gator include compass, gyro-turn indicator, thermometer, alti-
meter, air-speed indicator, watch, computers, prepared forms,
tables, and charts (maps) . Invariable existence of a wind at
some time during flight necessitates determination of wind ef-
fect upon movements of aircraft over the ground which will
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10-12
AIR CORPS FIELD MANUAL
not be precisely as indicated by basic instruments, compass,
and air-speed indicator.
■ 11. Instruments. — a. The compass is the directional instru-
ment and as such is one of the most important. Its errors
should be known and their method of application thoroughly
understood.
b. The gyro-turn indicator is used in conjunction with the
aircraft compass both as a reference instrument for precision
steering and as an amount indicator in making precision turns.
When used as a steering reference the gyro- turn indicator is
usually set at zero.
c. The thermometer is used to provide information for
correcting altimeter and air-speed readings for temperature
changes. These corrections are determined by computer.
d. The altimeter is used to determine height of the airplane
relative to terrestrial objects as a means of determining air
density for correction of air-speed indicator readings, and in
conjunction with some types of drift meters for determining
ground speed.
e. The air-speed indicator is the basic speed instrument.
Its indications, when corrected, give true speed of aircraft
through the air mass. Correction includes calibration for
installation errors and those for variation of air density from
standard. Corrections for air density (temperature and alti-
tude) may be determined by computer.
/. The watch is used as a navigational instrument to indi-
cate times of observations.
■ 12. Equipment. — a. Several types of air navigation com-
puters are employed. They are basically circular slide rules
permitting calculations of speed-time-distance and fuel-con-
sumption problems. Scales on the computers permit correc-
tion of air-speed meter readings for air density, and of alti-
meters for temperature changes. Instructions furnished with
particular computers explain their detailed use.
b. Charts available for use include a variety of projections
and forms. The pilot-navigator should be familiar with
comparative advantages and disadvantages of Mercator,
Lambert conformal, polyconic, and gnomonic projections and
be able to select and use the type of chart most suitable to
his needs.
4
AIR NAVIGATION
12-14
(1) The following aeronautical charts are now being pub-
lished by the U. S. Coast and Geodetic Survey:
(a) Sectional charts of the entire United States, in 87
sheets, at a scale of 1 : 500,000.
(b) Regional charts of the entire United States, in 17
sheets, at a scale of 1:1,000,000.
(c) Radio direction finding charts of the entire United
States, in 6 sheets, at a scale of 1:2,000,000.
(d) Aeronautical planning chart of the United States (No.
3060a), at a scale of 1:5,000,000.
(e) Great Circle chart of the United States (No. 3074) at
a scale of approximately 1:5,000,000.
(/) Magnetic chart of the United States (No. 3077) show-
ing lines of equal magnetic variation, at a scale of approxi-
mately 1:7,500,000.
(2) The U. S. Coast and Geodetic Survey also publishes
Mercator charts of territorial waters of the United States
and insular possessions, while the Hydrographic Office, U. S.
Navy, publishes charts of all oceans, seas, and bays of the
world on Mercator or gnomonic projections. These charts
include coastlines and show all marine navigation data avail-
able. Catalogs are available listing all charts published by
both agencies.
■ 13. Preflight Preparation. — a. Prior to take-off, the pilot-
navigator procures all necessary data and equipment and
arranges it for convenient use in flight. The use of a log
sheet on any type of air navigation mission is essential as a
means of insuring proper preparation and facilitates a con-
stant flight check. Proper charts should be selected and
prepared. Prom available wind data, drift corrections and
ground speeds are computed. These data are entered in the
log prior to take-off, together with estimated flight time to
reference landmarks.
5. A knowledge of existing and anticipated weather along
a contemplated flight course is necessary for intelligent prep-
aration and execution of a mission as pertaining both to
safety and air navigation of the flight.
■ 14. Mission. — a. A check of navigation instruments is
made while climbing in the general direction of the course,
or to some initial point previously selected. Upon arrival at
14-16
AIR CORPS FIELD MANUAL
selected altitude or initial point, the proper compass heading
is assumed and time noted.
b. In flight necessary changes in direction are determined
by locating position with reference to landmarks. Amount
of change may be determined from prepared tables. From
the determined time of flight for a known distance, speed and
estimated time of arrival (ETA) at other landmarks or desti-
nation may be computed.
c. During flight position is continuously checked and re-
corded in a log. These entries are supplemented by data on
course being flown and ground speed to permit computation
of dead reckoning position of the aircraft. The pilot-navi-
gator is more concerned with a knowledge of his position and
his subsequent ability to reach his destination than with the
execution of a precise navigation flight.
Section III
NAVIGATOR
■ 15. General. — a. Whenever precision navigation is re-
quired, navigation duties are assigned to a competent member
of the crew whose sole duty is that of navigator. Such as-
signment is especially desirable in aircraft of long flight
range. All methods of air navigation are normally available
to the navigator.
b. All instruments and equipment available to the pilot-
navigator are normally employed by the navigator. How-
ever, space and the opportunity to use other instruments and
equipment enlarge his capabilities for extensive and precise
navigation.
c. Celestial navigation methods and equipment are dis-
cussed in chapter 4.
■ 16. Instruments. — a. The aperiodic type compass is nor-
mally employed for precise navigation. The damping char-
acteristic of this compass makes it superior to other types for
precise reading.
b. A movable reference, or lubber line, that can be remotely
controlled by the navigator is a necessary adjunct to the
gyro-turn indicator for precision navigation.
6
AIR NAVIGATION
16
c. The drift meter is essentially a device used to measure
the angle between longitudinal axis of the airplane and di-
rection of motion of the airplane relative to the earth.
Amount of drift can be read directly from the instrument
and is designated as a drift angle right or left according to
the side toward which the wind is carrying the airplane, or
as a drift correction minus or plus, respectively, indicating
amount of angular correction to be applied to the course
to counteract effect of wind, and to obtain the heading . Use
of drift floats requires a back sighting or trail type drift
meter. Most drift meters serve also as ground speed meters.
The two general methods of determining ground speed by
measurement are —
(1) Timing. — Timing instruments use the geometrical rela-
tion of similar triangles to determine ground speed and
® Vertical type sight. ® Trail type sight.
Figure 1. — Ground speed determination.
7
16-17
AIR CORPS FIELD MANUAL
require a knowledge of the actual height or altitude above
the ground. Figure 1© illustrates use of the vertical type
sight and figure 1 © the trail type sight. Ground speeds
may be obtained from tables provided for the particular
instrument using the factors of time and absolute altitude
of flight.
(2) Multiple drift measurements. — To determine ground
speed from drift readings on two headings, two velocity tri-
angles are solved, the wind line closing the two triangles
and completing their solutions. The solution of a typical
problem of this sort is illustrated in figure 2.
measurements.
■ 17. Equipment. — a. Two types of aircraft chart boards are
available for use by navigators. One consists of a grid board
covered by a circular transparent plate pivoted at the center.
The other consists of a mounting board for charts which is
equipped with small arm protractors and scales. These boards
permit rapid solution of dead reckoning problems and assist
in plotting celestial observations.
b. The pelorus is an instrument used to obtain bearings on
terrestrial or celestial objects. This instrument may be a
8
AIR NAVIGATION
17
mechanical sighting device or it may be the optical type em-
ploying prisms and reflected images.
Each bearing gives a line of position, that is, a line on
which the aircraft is observed to be. The intersection of two
or more lines of position determines a fix or known position.
(1) Two bearings may be taken of the same object, in which
case the estimated distance flown is fitted in between the two
bearings so as to parallel the known course. This use of
bearings is illustrated in figure 3 ® .
Figure 3. — Bearings.
9
17-19
AIR CORPS FIELD MANUAL
(2) Two bearings may be taken of different objects, the first
bearing being carried forward by parallel motion the esti-
mated distance flown during the time interval between taking
the two bearings. This use of bearings is illustrated in figure
3<®.
c. Computers and calculators are used extensively in air
navigation. Computers used by the navigator are normally
the same as those used by the pilot-navigator but may be
larger and contain more data.
d. The navigator should be familiar with all types of chart
projections to enable him to select the proper chart for his
needs. He should also be familiar with calculation of course
and distance as applicable to the Mercator projection as that
projection is extensively used over water areas.
e. A navigation case provided with drafting equipment for
plotting purposes is available.
■ 18. Preflight Preparation. — Preparation for a mission by
the navigator is similar to that of the pilot-navigator but is
more detailed. Probable length and nature of the flight re-
quire that greater significance be placed upon the factors of
weather, terrain, and light, and the advantage of additional
instruments and equipment requires greater preparation to
assure their proper functioning in flight. A conference be-
tween the navigator, pilot, and airplane commander to deter-
mine courses to be flown, initial point, and altitude is an im-
portant element of preflight preparation.
■ 19. Mission. — a. Use of a definite procedure in making
corrections for drift, in determining ground speed, and in
their recording in the log is most important. Because it is
impossible to remember the great number of readings, cor-
rections, and calculations of speed, time, and distance, the
navigator should make it an inflexible rule to record all data.
Numerous forms are made available for this purpose.
b. Drift is read and heading changed at such intervals as
are necessary to maintain the desired course. Changes in
course are determined, based on location of position by pilot-
age, dead reckoning, radio aids, or celestial observations.
c. Ground speed is obtained and continually checked. The
distance made good is determined by pilotage, bearings on
terrestrial objects, radio bearings, or celestial lines of position.
10
AIR NAVIGATION
19
d. When for safety of aircraft detours must be made on
account of weather, the pilot is in the most advantageous
position to determine change or changes of heading necessary.
If heading is constantly changed to avoid some obstacle, se-
quence of dead reckoning may be lost. When confronted by
need for a change in heading, the pilot should decide defi-
nitely upon a safe heading, announce his intention to turn
to it, change to the new heading, and maintain it carefully
until a second change is necessary, or until a new course can
be established for completion of the mission under direction
of the navigator. In this manner continuity is not broken
and track of the airplane may be determined more readily.
e. Special problems of radius of action, intercept, and
search confront the navigator.
(1) Radius of action is determined by computing ground
speeds with reported winds on a given course and their ap-
plication to the distance— time x speed formula. The prob-
lem of returning to a base other than the point of departure
must be solved graphically. Graphical solutions for radius
of action problems are shown in figure 4 ® and ©.
(a) In figure 4 ® an aircraft departs from point A on
course AB with given wind AW and 3 fuel-hours (excluding
reserve). AC represents heading required to maintain the
designated course and is equal in length to air speedXfuel
hours. AD into the wind is equal in length to wind veloc-
ity x fuel hours. The line EP is the perpendicular bisector
of the line DC. The line GP is drawn parallel to the wind
to intersect the course at G. AG represents the radius of
action of the aircraft to return to point A.
(b) In figure 4 © an aircraft departs from point A on
course AB with given wind AD and 3 fuel -hours (excluding
reserve) and returns to point A'. AC represents the heading
required to maintain the designated course AB, and is equal in
length to air speed X fuel hours. A' D' into the wind is equal
in length to wind velocity X fuel hours. The line EP is the
perpendicular bisector of the line C' D\ The line GPis drawn
parallel to the wind to intersect the course at G. The length
of AG represents the radius of action of the aircraft to return
to point A'. The line GA' represents the course to point A\
11
AIR NAVIGATION
19
(2) The problem of interception is merely one of main-
taining a greater speed than the target and keeping it on a
constant bearing on converging lines. In figure 5, A is the
target maintaining a course AC at a known speed and B is
the intercepting craft. The line AB is drawn, joining the
respective positions of A and B at the same instant. If the
target alters its track, the problem must be reworked, starting
with the respective positions of the two craft at the same
instant.
(3) Search of a sea area is a specific navigation, problem
and normally involves only point-to-point navigation. The
search pattern depends upon tactical considerations which in-
clude aircraft available, size of area, visibility, and aircraft
range.
253155° — 40
3
13
CHAPTER 3
RADIO NAVIGATION
Paragraphs
Section I. Facilities and equipment 20-26
II. Practice 27-30
Section I
FACILITIES AND EQUIPMENT
■ 20. General. — One of the features of radio which is applied
to air navigation is that direction from which radio waves are
received may be determined fairly accurately by means of
directional characteristics of loop antenna. This same direc-
tional characteristic of a loop is also applicable to a limited
extent to transmission.
■ 21. Radio Ranges. — a. The equi-signal radio range is de-
signed to provide directional guidance for aircraft in flight.
The width of on-course signals of a radio range increases at
the approximate rate of 1 mile in 10 from the transmitting
station. As generally used, the range station employs two
loop antennas, the loops being energized respectively with
Morse signals, N ( — .) and A (. — ). The resultant aural
effect is N and A signals in alternate quadrants separated by
predetermined range courses where the two signals interlock
to give a continuous monotone sound. An N quadrant always
contains the direction of true north unless a course range is
on true north in which case the N quadrant is to the west.
The range courses need not be at right angles but may be
arranged within limits to suit directions of an air route. As
shown on airways charts and in radio range data all courses
are magnetic.
b. Radio ranges are subject to errors which must be deter-
mined to permit intelligent use of these facilities.
(1) Some ranges are subject to an error known as multiple
courses. This phenomenon results in additional on-course
signals bounded by distinct N and A zones, and roughly
parallel to the intended on-course range. Probability of this
condition occurring on a particular range has been deter -
14
AIR NAVIGATION
21
mined by experience and this information is available. The
only definite means of avoiding errors caused by multiple
courses is to maintain an additional check by pilotage or dead
reckoning.
(2) Terrain features also cause a bending of radio range
courses from their intended direction. Probability of this
error has likewise been determined by experience and that
information recorded and published. Pilotage and dead
reckoning again must be relied upon to avoid errors from
this cause.
(3) Particularly at sunset and sunrise but also at night a
swinging of some radio ranges occurs. However, this swing-
ing has a fairly definite period and is not particularly wide.
Its probability of existence has been determined and recorded.
Errors again must be avoided by pilotage and dead reckoning
check.
c. Radio ranges have a peculiarity which serves as a posi-
tion marker. This is the cone of silence which exists over the
transmitting antenna of the range. The cone of silence may
be recognized aurally by a complete fade-out of the signals
followed by a surge in strength greater than that existing
prior to reaching the cone of silence. This phenomenon
does not always occur directly over the station but may tilt
from the vertical to some extent. In some instances a false
cone of silence exists which is generally known and recorded.
Check of relative location of respective N and A zones near
the station, together with pilotage and dead reckoning checks,
will avoid errors due to a false cone of silence.
d. Almost all radio range stations are equipped for voice
transmission. Of the stations transmitting voice, some use
simultaneous range transmission while others interrupt the
range to transmit by voice on the same frequency. Weather
broadcasts are made from designated stations at times listed
for the particular station. In the simultaneous transmission
of range signals and weather, the voice frequency is one kilo-
cycle lower, permitting the operator by careful tuning to re-
ceive the weather information stronger than the range. Air-
ways control is exercised in accordance with Civil Aeronautics
Authority Regulations by voice transmission from certain
designated points. The Army Airways Communication Sys-
15
21-23
AIR CORPS FIELD MANUAL
T'
tem also maintains receiving and transmitting stations at
designated fields.
■ 22. Marker Beacons. — Marker beacons are used along the
airways to mark intersections of some ranges and other geo-
graphic points. Marker beacons are of two types.
a. Low power nondirectional beacons with a distance range
of less than 5 miles. These beacons are usually set on the
same frequency as the range on which they are located, or
on the same two frequencies as the two intersecting ranges
they locate.
b. (1) Low power fan beacons whose directional effect is
vertical (like an open fan) . These beacons are generally
placed on ranges near airports and serve as distance markers
on approaches. Marker fan beacons require a separate re-
ceiver set hooked up to a visual indicator, and all operate on
the same frequency (75 megacycles). Those installed by the
Civil Aeronautics Authority have identifying code indications
whereas those used by the Army Air Corps do not.
(2) Some of the later type radio ranges are equipped with
vertical cone-shaped marker beacons known as the “Z” type
which supplement position-marking effect of cones of silence.
These beacons operate on the same frequency as fan marker
beacons (75 megacycles) and actuate a visual indicator
hooked up to a special receiver.
■ 23. Loop Antennas. — The loop antenna is so constructed
that when coupled with a suitable receiver bearings may be
taken on distant radio stations by rotating the loop until the
signal is of minimum strength, at which time the plane of
loop is perpendicular to the great circle course to the trans-
mitting station. In practice, a visual indicator is used in
connection with the loop to indicate signal strength. The
loop as applied to aircraft may be fixed or free to rotate.
Loop receivers on metal aircraft are subject to electrical ef-
fects very similar to compass deviation which change direc-
tion of incoming signals. Consequently, the aircraft on which
a rotatable loop is installed should be swung and a tabulation
similar to a compass deviation card made of the errors. This
table of errors differs from a compass deviation card in that
errors are dependent upon direction of the loop relative to
16
AIR NAVIGATION
23-26
the airplane’s heading, and not on actual direction of the
loop relative to north. The fixed loop which is used normally
only as a homing device does not require swinging.
■ 24. Direction Finder Stations. — Direction finder stations
are located generally on the coasts and serve to best advan-
tage on overwater flights. These stations plot the position
of aircraft by means of radio bearings taken on the airplane.
They are organized in groups, usually of three stations, and
carefully located to avoid as much as possible interference
and errors caused by terrain or atmospheric conditions.
Direction finder stations require two-way transmission and
are not capable of handling any material volume of traffic.
They have a useful role as aids to air navigation but their
results should always be checked by other available means.
■ 25. Navigation Information. — Civil Aeronautics Authority
publications include charts of all installations and booklets
listing facilities, monthly Airways Bulletin, and when nec-
essary weekly Notices to Airmen show all changes. The Air
Corps publishes information on radio installations, facilities,
and weather broadcasts. Sectional and regional aeronau-
tical charts also give radio range and weather broadcast
information.
■ 26. Aircraft Radio Equipment. — Practically all Air Corps
aircraft carry receivers that may be set to operate in the
frequency band used by the Civil Aeronautics Authority Air-
ways Network, permitting reception of weather information
and use of the radio range system. Radio compasses (air-
craft radio direction finders) are installed in many Air Corps
aircraft. The loop is generally rotatable in installations in
larger aircraft and fixed in the smaller. Receivers to which
the loops are coupled are normally set to operate in the com-
mercial broadcast band, although most receivers are equipped
with two or more coils and a frequency switch permitting
selection of frequency band desired. Those aircraft equipped
with a radio compass usually have the receiver and cockpit
indicator used with the fan-type, Z-type, and Air Corps
marker beacons which are all on the same frequency. Visual
indicators used with present Air Corps radio compass installa-
tions indicate direction of turn required to obtain a zero
17
26-28
AIR CORPS FIELD MANUAL
reading (minimum signal strength) . When the transmitting
station is passed over, the sense of the visual indicator is re-
versed and turns which previously brought the indicator to
zero will increase the off -course indication. However, a zero
reading may still be obtained when flying away from a station
indicating that the longitudinal axis of the airplane, extended,
passes through the station departed from.
Section II
PRACTICE
■ 27. General. — a. Army aircraft when using Civil Aero-
nautics Authority airways facilities comply with all Civil
Aeronautics Authority Regulations.
b. Pilot-navigators and navigators should be sufficiently
familiar with radio facilities available and with operation
and use of equipment provided to secure the benefits of radio
aids to navigation.
■ 28. Use of Radio Ranges. — a. Radio range on-course or
equi-signal zones serve as known courses which the pilot
can follow by maintaining a reasonably steady heading ap-
proximating the magnetic course of the range. Occasional
changes may be necessary to maintain position on the range
and are indicated by change in signals received. Normally,
flight is conducted on the right hand side of a range where
the on-course signal has the faint letter signal of the zone
on that side impressed upon it. This is known as the twilight
zone . For greater accuracy, particularly when approaching
a range station and seeking the cone of silence, aircraft
should attempt to remain in the center of the equi-signal
zone.
b. Drift corrections to remain on the range may be deter-
mined by pilotage, dead reckoning, or by trial and error.
The latter method is the only recourse when instrument con-
ditions prevail and when no previous drift corrections have
been applied. To determine drift by this method, the mag-
netic course of the range is compared with the compass
course required to maintain the same position relative to the
on-course signal. To arrive at this position it is best to over-
correct both in changes necessary to regain lost position and
in the trial drift correction applied, then reduce these cor-
18
AIR NAVIGATION
28
rections gradually until the proper drift correction is ob-
tained. In other words, bracket the correction.
c. Ground speed may be obtained on radio ranges by sev-
eral methods. Marker beacons of all types and cones of
silence serve to indicate a position on a range course. From
successive known positions, distance and time are measured
Figure 6. — Identification of the quadrant and range courses, 90°
method.
and ground speed computed. Intersections of two ranges
may also be used as a fix to determine ground speed. This
is accomplished when flying a range by tuning to an inter-
secting range and timing the point of intersection. An area
position may be determined in a similar manner by tuning to
several nearby ranges, noting their quadrant identification,
and by elimination determining the area of position from
appropriate charts.
19
28
AIR CORPS FIELD MANUAL
d. The problem of quadrant orientation may present itself
to the pilot-navigator when but one radio range is available.
Several systems in use involve the assumption of certain defi-
nite flight courses until a range is intercepted and identified,
using increase or decrease in signal strength as an indication
of approach to or departure from the transmitting station.
Most systems require courses that are either parallel or per-
pendicular to the bisecting azimuth of the respective N and
Figure 7. — Identification of the quadrant and range courses, fade-
out method.
A quadrants. The best systems are generally a combination
of definite intercept courses with the aural feature of change
in signal strength. Two of the systems used are illustrated in
figures 6 and 7. The particular method selected will depend
upon training and familiarity of the pilot with that method,
and by terrain characteristics in the vicinity of a particular
range and angular acuity of the courses of the particular
range.
20
AIR NAVIGATION
29-30
■ 29. Use of Radio Compass. — a. (1) Use of the fixed loop
permits aircraft to be navigated to a transmitting station by
keeping the pointer of the radio compass indicator centered.
Simplicity of this procedure and availability of many com-
mercial broadcast stations make this method of air naviga-
tion of great value. When using a fixed loop in this manner,
the aircraft is always kept headed toward the transmitting
station with the result that a cross wind causes a curved
track to be flown. This fact is of no great concern if the loop
is used as a homing device on relatively short flights. On
long flights, however, the loop should be used only as a means
of taking bearings in conjunction with use of other forms of
air navigation.
(2) The fixed type loop permits bearings to be taken on
two or more transmitting stations but involves maneuver of
the airplane. Head or tail bearings may be taken, the sense
of the visual indicator as compared to direction of turn being
used to determine whether direct or reciprocal bearings are
obtained.
b. The rotatable type loop is of great advantage, as it per-
mits taking bearings without changing heading of the air-
plane. Moreover, corrections may be made more readily for
drift when the radio compass is used as a homing device by
rotating the loop. Corrections for radio compass errors must
always be applied. When Mercator charts are used, bear-
ings are converted from great circle to Mercator by use of
radio bearing correction tables. Radio bearings are gener-
ally converted to reciprocal true bearings and used in the
same manner as bearings taken by a pelorus.
■ 30. Direction Finder Stations. — When a position is to be
obtained from radio direction finder stations, the aircraft
radio operator calls the controlling station of the group and
transmits his call sign or M-signals for a short interval
while the three stations take simultaneous bearings. The
control station receives all these bearings, plots them on a
special chart, and the position represented by the inter-
section of the bearings or the course necessary to arrive at
one of the stations is transmitted to the aircraft. The pro-
cedure for requesting these bearings is contained in U. S.
Hydrographic Office Publication No. 205.
21
CHAPTER 4
W"
CELESTIAL NAVIGATION
Paragraphs
Section I. General 31-33
II. Instruments and equipment 34-39
III. Celestial line of position 40-47
IV. Preflight preparation 48-50
V. Practice 51-59
Section I
GENERAL
■ 31. Definition. — Celestial navigation is the method of
determining geographical position of aircraft by observation
of celestial objects.
■ 32. Employment. — a. Range capabilities of modern aircraft
make necessary a form of navigation by which position infor-
mation can be obtained without recourse to terrestrial or
radio aids. Celestial navigation makes use of the sun, stars,
planets, and moon to obtain such information and thus pro-
vides a self-contained method of determining positive posi-
tion within limits of equipment used and weather conditions
prevailing.
b. Celestial navigation is not an independent form of air
navigation but is employed to verify or correct the other
forms. The study or practice of celestial air navigation thus
requires a thorough knowledge of the other methods.
■ 33. Terminology. — Definition and application of terms em-
ployed in this form of air navigation must also be thoroughly
understood. The glossary contained in the appendix gives
brief definitions of navigation terms not defined elsewhere
in this manual.
Section n
INSTRUMENTS AND EQUIPMENT
■ 34. Octant. — The octant is an optical device for measuring
the angular height of a body above a horizontal plane. This
measurement in celestial navigation is called altitude. A bub-
ble is incorporated in the aircraft octant instrument to indi-
22
AIR NAVIGATION
34-40
cate horizontal plane. The octant is a precision instrument
and must be carefully handled.
■ 35. Timepiece. — An accurate timepiece is required to obtain
correct results from celestial observations. In the larger type
aircraft a master watch or clock is provided in a shockproof
case. In addition to the master watch or as a substitute
therefor, a second-setting wrist or pocket watch is generally
employed in making observations.
■ 36. Forms. — The chance of error in making calculations
necessary to obtain data desired from celestial observations
may be reduced considerably by employing tabular forms
specially prepared for the method being used. These forms
are arranged so as to permit speed with accuracy.
■ 37. Tables. — First in importance among the tables used is
the American Nautical Almanac, a yearly publication of the
Hydrographic Office, U. S. Navy. The Almanac lists the posi-
tions of celestial bodies used for navigation purposes so that
their precise locations at any instant during the year may be
determined. In addition to the Almanac other tables are
required if no computer is used. Other tables include Dead
Reckoning Altitude and Azimuth Table (Ageton) (H. O. 211)
and the Tables of Computed Altitude and Azimuth (H. O. 214) .
■ 38. Computers. — The astronomical triangle (see par. 41)
may be solved by a computer designed for the purpose insteac
of by tables. Selection of computer or tabular method o
solution depends on availability of equipment, space, an<
reliability of computers available.
■ 39. Star Finder. — A star finder is desirable for proper plan-
ning and execution of a celestial navigation flight. Under ad-
verse weather conditions star identification is facilitated by
use of such a device. The Rude Star Finder (H. O. 2102a)
produced by the Hydrographic Office has been developed for
use indicated. Star identification tables and charts are also
found in other publications on celestial navigation.
Section HI
CELESTIAL LINE OF POSITION
■ 40. Basic Principle. — The observed altitude of a heavenly
body at any instant locates the observer on a circle circum-
23
40-41
AIR CORPS FIELD MANUAL
scribed about the geographical position of that body at the
instant of observation (see fig. 8) . This is a position circle
whose radius is determined by the altitude measured. If two
bodies may be observed simultaneously and the position circles
of the observer determined, their points of intersection become
positive positions. Computations aided by dead reckoning
provide the means of determining that portion of the position
circle or the point of intersection of two position circles ap-
plicable to the flight path, and also data for plotting applicable
portion of position circle (s) on a chart. These computations
are performed in solution of the astronomical triangle.
■ 41. Astronomical Triangle. — This triangle is formed by the
great circle arcs joining assumed position of the observer,
24
AIR NAVIGATION
41-43
geographical position of the celestial body at the instant of
observation, and nearest pole (see fig. 9).
■ 42. Assumed Position of Observer. — Assumed position of
the observer may be the dead reckoning position at time of
observation but more generally is one selected arbitrarily in
the vicinity of the dead reckoning position. Selection of an
assumed position depends upon method of solution and is so
made as to facilitate process of solution. This arbitrary
assumption of position introduces no appreciable error in
resulting position circle.
■ 43. Geographical Position of a Celestial Body. — The geo-
graphical position of a celestial body is that point on the
earth’s surface which is exactly under a given heavenly body
25
43
AIR CORPS FIELD MANUAL
at any one instant. An observer at the geographical posi-
tion would find the corresponding body exactly at his zenith.
The geographical position of a heavenly body is generally
designated by declination and Greenwich hour angle, which
are in reality latitude and longitude. The correct Greenwich
Civil Time and the Nautical Almanac provide the means of
obtaining these coordinates, declination, and Greenwich hour
angle having been tabulated for a specific body at a specific
instant. In most solutions of the astronomical triangle the
local hour angle is used. This is the angular difference be-
tween the Greenwich hour angle of the body and the longi-
tude of the observer's assumed position as measured from the
assumed meridian of the observer. The use of a diagram as
shown in figure 10 is desirable in finding the local hour angle.
Figure 10. — Hour angle diagram.
26
AIR NAVIGATION
44-46
■ 44. Observed Altitude. — The octant altitude (Hs) of a
body is determined by measurement with an octant. Time
of observation determines geographical position of the heav-
enly body at the instant its altitude was measured. Correc-
tions may be necessary to the octant altitude to obtain
observed altitude (Ho). Values of corrections and various
combinations of corrections are tabulated in celestial naviga-
tion publications. These corrections are as follows:
a. Correction must be made for dip when using natural
horizon; amount of correction depends upon height of eye
of the observer above the earth’s surface. No such correction
is required with an artificial horizon.
b. Correction must also be made for refraction errors due
to bending of light rays by the atmosphere.
c. In observations of the sun or moon correction, must be
made to allow for diameters of these bodies. This is known
as correcting for upper or lower limb of the body, depending
upon whether measurement was made to upper or lower edge
of the periphery.
d. In observations of the moon correction also must be
made for parallax due to its relative proximity to the earth.
e. Index errors in the scale of the particular octant are
determined by precision measurements and are recorded on
an index error card. The zero index error may {je satis-
factorily determined by the navigator as prescribed in man-
uals pertaining to the particular instrument.
■ 45. Computed Altitude. — Computed altitude (He) of a
body is the altitude- computed for assumed position at in-
stant of observation. It is found by subtracting computed
zenith distance of the body observed from 90° (see fig. 11).
Zenith distances obtained from observed and computed alti-
tudes are the radii of the position circles passing through
the observer and the assumed position respectively. The
angular distance from position circle of an observer to an
assumed position can therefore be determined by arithmetical
difference between computed and observed altitudes of a ce-
lestial body at the instant of observation.
■ 46. Azimuth. — Azimuth from assumed position to geo-
graphical position of a heavenly body is determined by
27
46-47
AIR CORPS FIELD MANUAL
solution of the astronomical triangle. This azimuth serves
to identify segments of the position circle applicable to the
particular problem.
Figure 11. — Zenith distance and observed altitude complementary.
■ 47. Plotting. — In plotting a segment of a position circle
a straight line is used. This line is known as a line of
position (LOP) and is drawn perpendicular to the computed
28
47-51
AIR CORPS FIELD MANUAL
a. Plot assumed position and through it draw computed
azimuth line.
b. Find altitude difference between observed (Ho) and com-
puted altitudes (He) in minutes of arc.
c. From assumed position lay off as a distance altitude
difference (1 minute of arc equals 1 nautical mile) along
azimuth line, either toward or away from the celestial body
as observed altitude is respectively greater or less than
computed altitude.
d. Through this point draw a line perpendicular to azi-
muth line. This is the line of position of the observer.
Section IV
PREFLIGHT PREPARATION
■ 48. General. — Prior to flight the navigator makes such
preliminary computations as are possible and assures him-
self that he is provided with all necessary instruments and
equipment.
■ 49. Check of Watch. — The master watch is an instru-
ment of extreme importance in celestial navigation. Check-
ing this instrument for determining its rate is a continuous,
periodic duty. Actual reading of a watch is unimportant so
long as the watch error can be determined. Watches are
checked by reference to radio time signals which are broad-
cast by both commercial and governmental agencies daily.
(See Radio Aids to Navigation, H. O. No. 205.)
■ 50. Check of Octant. — The index error of the octant used
by the navigator should be known. Personal error should be
determined by a series of observations taken from a rigid
support and compared with computed data.
Section V
PRACTICE
■ 51. General. — Applied celestial navigation embraces use
of lines of position by the navigator in a manner that en-
ables him to determine drift, ground speed, or position in
order that serious errors do not enter into dead reckoning.
To obtain basic data for these determinations the navigator
must first make his celestial observations.
30
AIR NAVIGATION
52-56
■ 52. Celestial Observations. — Celestial observations from
aircraft are normally made in groups of ten or more averag-
ing altitudes read and times of observations. Corrected ob-
served altitude (Ho) and time are then reduced by precom-
puted data or by tables and forms available, and plotted as
a line of position. Observations are taken in groups and
averaged in an effort to reduce the resultant value of error
due to* acceleration, manipulation, and other causes inherent
in the bubble type octant. Observations made in fore and
aft direction of aircraft are generally less subject to accelera-
tion error than lateral observations.
■ 53. Time Factor. — Successful air navigation demands ra-
pidity and accuracy in reduction of celestial observations to
usable data. Development of averaging devices, tables,
forms, and computers has decreased time required. Proper
technique and skill in use of instruments are necessary to
obtain satisfactory results.
■ 54. Weather Conditions. — Weather conditions may be such
as to make identification of heavenly bodies difficult. In
such case it is advisable to make observations whenever pos-
sible, and then with an estimated bearing determined from
the heading and the time, a star finder may be utilized to
identify the body observed.
■ 55. Interpretation of Data. — Proper interpretation by the
navigator of the data derived from a plotted line of position
is important. A single position line or successive position
lines, if approximately parallel to the course, will give accu-
rate information as to directional or on-course position.
Position lines cutting the course at near right angles will
give accurate distance information from which ground
speed may be derived. Intersection of two or more lines
of position will establish a fix and give both directional and
distance information.
■ 56. Obtaining Fix. — Celestial lines of position may be
treated in the same manner as bearing lines. In this manner,
a fix may be obtained by the intersection with other lines
of position. In obtaining a fix the celestial radio or terres-
trial lines of position used should be so selected that they
intersect as nearly at right angles to each other as prac-
31
56-59
AIR CORPS FIELD MANUAL
ticable. This insures a sharp intersection and consequently
greater accuracy.
■ 57. Celestial Bodies Available. — Information as to celes-
tial bodies that will be available during a proposed flight can
be secured by the navigator by use of a star finder and the
Nautical Almanac. Type of information desired (whether
directional or distance) and possibility of a fix are consid-
ered in selection of bodies for precomputation of data.
■ 58. Precomputation of Data. — Precomputation of data
saves time and increases accuracy of information derived
from celestial observations. Precomputation involves thor-
ough study of the flight plan, considering factors of celestial
bodies available, possibility of day or night observations, and
time of flight. This information permits the navigator actu-
ally to make certain calculations prior to take-off. Small
corrections may be necessary to compensate for the differ-
ence between time and azimuth of precomputed data and
data derived from actual observation. No serious error in
data obtained is thus introduced.
a. Course curves of precomputed altitudes and azimuths
for a body may be drawn, using as assumed positions dead
reckoning positions at equal time intervals.
b. Computed altitudes and azimuths may be determined,
the altitudes being recorded and azimuths actually plotted
through dead reckoning positions used as assumed positions
on proposed flight course.
c. Prepared simultaneous star altitude curves may be used
to obviate necessity of precomputing star data.
■ 59. Landfall Method of Reaching Destination. — The land-
fall method is valuable for reaching a destination under con-
ditions where only one heavenly body may be observed. This
method enables the navigator to gain a position on a bearing
line from the destination with a degree of accuracy limited
only by results of celestial navigation performed. Procedure
followed is basically the same whether one or more observa-
tions are made. Precomputed data is generally employed
based on estimated time of arrival at a point some distance
from the destination with destination as assumed position.
The airplane is headed well to one side of the objective. At
32
AIR NAVIGATION
59
the preselected time for which computations were made, one
or more observations are taken. Then according to whether
observed altitude is less or greater than computed altitude,
the navigator takes up a course of the computed azimuth
or its reciprocal, respectively, flying for a distance equal to
the altitude difference (distance between observed line of
position and line of position through destination). This
places him on the position line passing through the destina-
tion. Once on this line the course to the destination is the
azimuth plus or minus 90°. The initial course is laid to one
side of the destination to eliminate possibility of error in
selection of direction of turn.
a. When but one observation is to be made, time used in
precomputation of data is estimated time of arrival at a
point whose estimated distance from the destination renders
the dead reckoning dependable.
b. When more than one observation is to be made, a sta-
tionary curve for the assumed position (the destination) is
prepared covering the period of time during which contem-
plated observations are to be made. This method enables
the navigator to make continued checks on his dead reckon-
ing after landfall procedure is initiated.
33
Appendix
GLOSSARY OP TERMS
Air Speed . — True speed of an aircraft relative to the air.
It is the true air speed unless otherwise stated. Air speed
is obtained by correcting calibrated air speed for density,
using temperature and pressure altitude corrections.
Indicated. — Reading of air-speed indicator.
Calibrated. — Reading of air-speed indicator corrected
for instrumental and installation errors.
Altitude. — True height above sea level. The calibrated
altitude corrected for air temperature and for barometric
pressure. It is always true unless otherwise designated.
Indicated. — Height above sea level as read on altimeter.
Calibrated. — Indicated altitude corrected for instru-
mental and installation errors.
Absolute. — True height above the earth’s surface. It
is calibrated absolute altitude corrected for air tem-
perature and barometric pressure.
Azimuth. — Bearing of a celestial body measured as an arc
on the horizon from the true meridian north or south to
east or west. Abbreviation: Z. Abbreviation Zn is used
where the azimuth has been changed to read from north
through east to 360°.
Bearing. — Direction of one object from another expressed
as an angle measured clockwise from true north. Bearing is
true unless otherwise designated. Abbreviation: B.
Compass. — An instrument indicating angle of longitudinal
axis of aircraft with respect to axis of compass needle. Taken
to be a magnetic compass unless otherwise designated.
Aperiodic . — A cardless magnetic compass in which the
needle when deflected from its point of rest returns
to that point with small overswing.
Error. — Algebraic sum of variation and deviation. Ab-
breviation: C. E.
Course. — Direction over surface of the earth expressed as
an angle with respect to true north that an aircraft is
intended to be flown. It is the course laid out on the chart
35
AIR CORPS FIELD MANUAL
or map and is always the true course unless otherwise desig-
nated. Abbreviation: C. All courses are measured from
north through east to 360°.
Curves . — Stationary. — Plotted graph of computed altitude
or azimuth of a celestial body for a fixed position
with time as the abscissa.
Course. — Plotted graph of altitude or azimuth of a
celestial body computed for dead reckoning positions
on a flight course at equal time intervals.
Simultaneous Star Altitude. — Plotted position circles
of selected stars on a small Mercator chart covering
10° or 11° of latitude and 360° of longitude. These
curves are generally prepared in booklet form.
Declination. — Angular distance of any point on celestial
sphere from celestial equator measured along the great circle
through the celestial pole. It is designated north or south
according to direction of the point from celestial equator.
Declination upon the celestial sphere corresponds to latitude
on the earth.
Deviation. — Angular error between axis of the compass
needle and magnetic meridian caused by magnetic influences
in the aircraft and is named east or west according to direc-
tion in which needle is deflected.
Dip. — Amount of angular depression from the horizontal
line through the eye of an observer to a line to visible
horizon.
Distance. — Distance may be expressed as statute or nau-
tical miles. A statute mile is an arbitrary measurement and
is equal to 5,280 feet. A nautical mile is the length of l min-
ute of latitude, and for practical purposes is taken as 6,080
feet.
Drift Float. — An article or substance dropped from an air-
craft over water, forming a point of reference for observing
drift angle or surface wind direction.
Great Circle. — A circle on the earth’s surface whose plane
passes through the center of the earth.
Greenwich Hour Angle. — Angle at the pole between merid-
ian of Greenwich and meridian through a celestial body
measured from meridian of Greenwich to the west 0° to 360°.
36
AIR NAVIGATION
Heading. — Angular direction of longitudinal axis of the air-
craft with respect to true north. In other words it is the
course with drift correction applied. It is true heading
unless otherwise designated.
Knot. — Unit of speed used in navigation, and equal to a
speed of 1 nautical mile per hour. (Equivalent to 1.15 statute
miles per hour.)
Latitude. — Angular distance north or south of the equator
as subtended at the center of the earth measured from the
equator as a plane of origin. Abbreviation: Lat.
Longitude. — Angular distance at axis of the earth between
plane of meridian and plane of the prime meridian of Green-
wich, England, measured to eastward or westward to 180°.
Abbreviation: Long.
Lubber Line. — A fixed line inside a compass bowl so placed
that a plane through it and center of the compass pivot is
parallel to a plane through longitudinal and vertical axes
of the aircraft. The lubber line represents direction of the
longitudinal axis of the aircraft.
Mercator Course (Rhumb line) . — A line on the earth’s sur-
face which intersects all meridians at the same angle.
Off-course Correction. — An angular correction applied to
the course to parallel or to return to original course in a
given distance.
Parallax. — The angle contained between the two straight
lines joining a heavenly body and two different points on the
earth.
Radio Direction Finder. — A radio receiving unit incorporat-
ing use of loop antenna for obtaining direction of trans-
mitted signals. The aircraft installation is known as a
radio compass.
Temperature. — Air. — Temperature of the air at altitude be-
ing maintained by aircraft.
Variation. — Angle between plane of true meridian and a
line passing through a freely suspended compass needle in-
fluenced solely by the earth’s magnetism. It is named east
or west according to direction of the compass needle from
true north. Variation changes with time and place. Abbre-
viation: Var.
37
AIR CORPS FIELD MANUAL
Wind Direction and Force. — Wind is designated by direc-
tion from which it blows. Force of wind is expressed as
speed in miles per hour or knots.
Zenith. — Zenith is the point of the celestial sphere ver-
tically over a terrestrial position.
Zenith Distance. — Angular distance of a celestial body
from observer’s zenith.
INDEX
Paragraph Page
Absolute altitude definition App. 35
Acceleration error 52 31
Aeronautical planning charts 12 4
Air Corps circulars 6 2
Aircraft chart boards 17 8
Aircraft radio equipment 26 17
Air navigation mission 14, 19 5, 10
Air-speed indicator 11 4
Air speed, definition App. 35
Air temperature, definition App. 37
Airways bulletin, issue 25 17
Airways Communications System, Army 21 14
Almanac, Nautical. See Nautical Almanac.
Altimeter 11 4
Altitude computed, of celestial body 45 27
Altitude curves, simultaneous star 58, App. 32, 36
Altitude:
Celestial navigation 34 22
Definition App. 35
Difference 47 28
Observed 44 27
Octant, corrections 44 27
Angle, Greenwich and local hour 43 25
Antenna, loop 20,21,23 14,16
Aperiodic compass:
Definition App. 35
Use 16 6
Army Airways Communications System 21 14
Artificial horizon 44 27
Astronomical triangle 38,40,41,46 23,24,27
Azimuth :
Definition App. 35
Determination 46 27
Beacons, marker 22 16
Bearings 17, App. 8, 35
Boards, aircraft chart 17 8
Bubble octant 52 31
Calculators 17 8
Calibrated air speed and altitude, definition App. 35
Card, index error 44 27
Case, navigation 17 8
Celestial body:
Available during flight, information 57 32
Geographical position 43 25
Celestial line of position 40-47 23-28
Celestial navigation 31-59 22-32
Celestial observations 52 31
Chart boards 17 8
Charts 12 4
39
r
INDEX
Check : Paragraph Page
Octant 50 30
Watch 49 30
Civil Aeronautics Authority:
Publications 25 17
Regulations, compliance 21, 27 14, 18
Civil time, Greenwich 43 25
Cone of silence, radio range 21 14
Conformal projection, Lambert 12 4
Compass :
Aperiodic 16 6
Definition App. 35
Employment, purpose 11 4
Error, definition App. 35
Radio, use 29 21
Computers :
Astronomical triangle 38 23
Use 12 4
Corrections:
Drift, to remain on radio range 28 18
Octant altitude 44 27
Off-course, definition App. 37
Course :
Curve, definition App. 36
Definition App. 35
Mercator, definition App. 37
Curves, definition App. 36
Dead reckoning 8 3
Declination, use and definition 43, App. 25, 36
Definition :
Air navigation 2 1
Celestial navigation 31 22
Destination, landfall method of reaching 59 32
Deviation, definition App. 36
Difference, altitude 47 28
Dip:
Correction for 44 27
Definition App. 36
Direction finder:
Radio, definition App. 37
Stations 24,30 17,21
Distance :
Definition App. 36
Zenith 45, App. 27, 38
Drift:
Corrections to remain on radio range 28 18
Floats 16, App. 6,36
Meter 16 6
Employment:
Air navigation 3 1
Celestial navigation 32 22
Equipment 12, 17, 20-26, 34-39 4, 8, 14-17,
22-23
Equi-signal radio range 21 14
Errors :
Index, octant 44 27
Refraction 44 27
40
INDEX
Fan beacons.
Geographical position, celestial body.
Gnomonic projection.
Greenwich Civil Time.
Greenwich hour angle
Great circle:
Chart
Ground speed meters
Ground speed obtained on radio ranges.
Gyro-turn indicator
Horizon, artificial .
Index errors, octant-
initial point-
intercept problems.
gation
Knot, definition App.
Landfall method of reaching destination
Lambert conformal projection
Limb, upper or lower, sun or moon.
Line of position
Interpretation
Plotting
Local hour angle.
Log sheet
Magnetic chart
Manipulation error
Manuals, technical, use.
Marker beacons
Mercator:
Course, definition. _
Projection
Paragraph
Page
22
16
... 17,56
8,31
16, App.
6, 36
36
23
43
25
... App.
35
12
4
43
25
43, App.
25,36
12
4
— App.
36
16
6
28
18
11
4
16, App.
6, 37
44
27
. 43, App.
25,36
ili-
12,30,37 2,4
,21,23
44
27
... App.
35
__ App.
35
14
5
-26,34-39 1,
4, 6—8,
14-17,
22-23
19
10
vi-
55
31
.. App.
37
59
32
12
4
. 43, App.
25, 37
44
27
17
8
__ 40-47
23-28
55
31
47
28
._ App.
37
43
25
13
5
43, App.
25,37
20,21,23
14,16
16, App.
6,37
12
4
52
31
6
2
22
16
__ App.
37
12
4
41
INDEX
Method: Paragraph Page
Landfall, reaching destination 59 32
Pilotage and dead reckoning, treatment 9 3
Mission, air navigation 14, 19 5, 10
Multiple courses on radio range 21 14
Multiple drift measurements 16 6
Nautical Almanac, use 6, 37, 43, 57 2, 23,
25, 32
Navigation mission, air 14, 19 5, 10
Navigator 5, 10-19 1, 3-10
Navy publications, Hydrographic Office 6 2
Notices to airmen 25 17
Observations, celestial 52 31
Observed altitude 44 27
Observer, assumed position 42 25
Octant 34, 44, 50 22, 27, 30
Off -course correction, definition App. 37
Orders, technical 6 2
Orientation, quadrant on radio range 28 18
Parallax 44, App. 27, 37
Pelorus 17 8
Pilotage and dead reckoning 7-19 3-10
Pilot -navigator 10-14 3-5
Point, initial 14 5
Polyconic projection 12 4
Position :
Celestial line 40-47 23-28
Celestial body, geographical 43 25
Circle 40 23
Observer, assumed 42 25
Position line 17 8
Interpretation 55 31
Plotting 47 28
Practice :
Celestial navigation 51-59 30-32
Radio navigation 27-30 18-21
Precomputation of data 58 32
Preparation, preflight 13, 18, 48-50 5, 10, 30
Problems, radius of action, intercept, search 19 10
Projection, Mercator, Lambert conformal, poly-
conic, gnomonic 12 4
Publications, list and scope 6 2
Quadrant orientation on radio range 28 18
Radio :
Compasses 26, 29 17, 21
Direction finder:
Stations 24 17
Term defined App. 37
Use 26 17
Direction finding charts 12 4
Equipment, aircraft 26 17
42
INDEX
Radio-Continued .
Navigation : Paragraph
Facilities and equipment 20-26
Information 25
Practice 27-30
Ranges 21-28
Time signals 49
Radius of action problems 19
Ranges, radio 21, 28
Reference publications 6
Refraction errors 44
Regional charts 12
Responsibility, instrument 5
Rhumb line, term defined App.
Page
14-17
17
18-21
14-18
30
10
14, 18
2
27
4
1
37
Search problems 19
Sectional charts 12
Signals, radio time 49
Silence, cone of, radio range 21
Simultaneous star altitude curves 58, App.
Speed, air, term defined App.
Star altitude curves, simultaneous 58, App.
Stationary curve, term defined App.
10
4
30
14
32, 36
35
32,36
36
Tables used in celestial navigation 37
Technical manuals and orders 6
Temperature, term defined App,
Terminology, celestial navigation 33
Thermometer 11
Time factor, celestial navigation 53
Time, Greenwich Civil 43
Timepiece 35
Time signals, radio 49
Trail drift meter 16
Triangle, astronomical 38, 40, 41, 46
Turn indicator, gyro 11
Twilight zone 28
23
2
37
22
4
31
25
23
30
6
23, 24, 27
4
18
Variation, term defined
App. 37
Watch 11,35,49 4,23,30
Weather 13,54 5,31
Wind direction and force, term defined App. 38
Zenith
43,45, App. 25,27,38
O
43