Navigation
Chapter 16
Introduction
This chapter provides an introduction to cross-country
flying under visual flight rules (VFR). It contains practical
information for planning and executing cross-country flights
for the beginning pilot.
Air navigation is the process of piloting an aircraft from
one geographic position to another while monitoring one’s
position as the flight progresses. It introduces the need for
planning, which includes plotting the course on an aeronautical
chart, selecting checkpoints, measuring distances, obtaining
pertinent weather information, and computing flight time,
headings, and fuel requirements. The methods used in this
chapter include pilotage—navigating by reference to visible
landmarks, dead reckoning—computations of direction and
distance from a known position, and radio navigation—by
use of radio aids.
Figure 16-1. Sectional chart and legend.
Aeronautical Charts
An aeronautical chart is the road map for a pilot flying under
VFR. The chart provides information that allows pilots to track
their position and provides available information that enhances
safety. The three aeronautical charts used by VFR pilots are:
• Sectional
• VFR Terminal Area
• World Aeronautical
A free catalog listing aeronautical charts and related
publications including prices and instructions for ordering is
available at the Aeronautical Navigation Products website:
www.aeronav.faa.gov.
Sectional Charts
Sectional charts are the most common charts used by pilots
today. The charts have a scale of 1:500,000 (1 inch = 6.86
nautical miles (NM) or approximately 8 statute miles (SM)),
which allows for more detailed information to be included
on the chart.
The charts provide an abundance of information, including
airport data, navigational aids, airspace, and topography.
Figure 16-1 is an excerpt from the legend of a sectional
chart. By referring to the chart legend, a pilot can interpret
most of the information on the chart. A pilot should also
check the chart for other legend information, which includes
air traffic control (ATC) frequencies and information on
airspace. These charts are revised semiannually except for
some areas outside the conterminous United States where
they are revised annually.
VFR Terminal Area Charts
VFR terminal area charts are helpful when flying in or near
Class B airspace. They have a scale of 1:250,000 (1 inch
= 3.43 NM or approximately 4 SM). These charts provide
a more detailed display of topographical information and
are revised semiannually, except for several Alaskan and
Caribbean charts. [Figure 16-2]
World Aeronautical Charts
World aeronautical charts are designed to provide a standard
series of aeronautical charts, covering land areas of the world,
Figure 16-2. VFR Terminal Area Chart and legend.
at a size and scale convenient for navigation by moderate speed
aircraft. They are produced at a scale of 1:1,000,000 (1 inch =
13.7 NM or approximately 16 SM). These charts are similar to
sectional charts, and the symbols are the same except there is
less detail due to the smaller scale. [Figure 16-3] These charts
are revised annually except several Alaskan charts and the
Mexican/Caribbean charts, which are revised every 2 years.
Latitude and Longitude (Meridians and
Parallels)
The equator is an imaginary circle equidistant from the poles
of the Earth. Circles parallel to the equator (lines running east
and west) are parallels of latitude. They are used to measure
degrees of latitude north (N) or south (S) of the equator. The
angular distance from the equator to the pole is one-fourth
of a circle or 90°. The 48 conterminous states of the United
States are located between 25° and 49° N latitude. The arrows
in Figure 16-4 labeled “Latitude” point to lines of latitude.
Meridians of longitude are drawn from the North Pole to the
South Pole and are at right angles to the Equator. The “Prime
Meridian,” which passes through Greenwich, England, is
used as the zero line from which measurements are made in
degrees east (E) and west (W) to 180°. The 48 conterminous
states of the United States are between 67° and 125° W
longitude. The arrows in Figure 16-4 labeled “Longitude”
point to lines of longitude.
Any specific geographical point can be located by reference
to its longitude and latitude. Washington, D.C., for example,
is approximately 39° N latitude, 77° W longitude. Chicago
is approximately 42° N latitude, 88° W longitude.
Time Zones
The meridians are also useful for designating time zones. A
day is defined as the time required for the Earth to make one
complete rotation of 360°. Since the day is divided into 24
hours, the Earth revolves at the rate of 15° an hour. Noon is
the time when the sun is directly above a meridian; to the
west of that meridian is morning, to the east is afternoon.
Figure 16-4. Meridians and parallels—the basis of measuring time,
distance, and direction.
Longitude
L
a
titu
d
e
Equator Equator
75°N
60°N
45°N
30°N
15°N
15°S
30°S
45°S
60°S
90°N
75°N
60°N
45°N
30°N
15°N
15°S
30°S
45°S
60°S
90°N
1
5
0
°W
1
3
5
°W
120°W
105°W
90°W
7
5
°W
60°W
45°W
3
0
°W
1
5
°
W
P
rim
e m
eridian
1
5
0
°W
1
3
5
°W
120°W
105°W
90°W
7
5
°W
60°W
45°W
3
0
°W
1
5
°
W
P
rim
e m
eridian
Figure 16-3. World aeronautical chart.
The standard practice is to establish a time zone for each
15° of longitude. This makes a difference of exactly 1 hour
between each zone. In the conterminous United States,
there are four time zones. The time zones are Eastern (75°),
Central (90°), Mountain (105°), and Pacific (120°). The
dividing lines are somewhat irregular because communities
near the boundaries often find it more convenient to use time
designations of neighboring communities or trade centers.
Figure 16-5 shows the time zones in the conterminous United
States. When the sun is directly above the 90th meridian, it
is noon Central Standard Time. At the same time, it is 1 p.m.
Eastern Standard Time, 11 a.m. Mountain Standard Time,
and 10 a.m. Pacific Standard Time. When Daylight Saving
Time is in effect, generally between the second Sunday in
March and the first Sunday in November, the sun is directly
above the 75th meridian at noon, Central Daylight Time.
These time zone differences must be taken into account
during long flights eastward—especially if the flight must
be completed before dark. Remember, an hour is lost when
Figure 16-5. Time zones in the conterminous United States.
105°
120°
90°
75°
Mountain standard time Central standard time Eastern standard timePacific standard time
flying eastward from one time zone to another, or perhaps
even when flying from the western edge to the eastern edge
of the same time zone. Determine the time of sunset at the
destination by consulting the flight service station (FSS) and
take this into account when planning an eastbound flight.
In most aviation operations, time is expressed in terms of
the 24-hour clock. ATC instructions, weather reports and
broadcasts, and estimated times of arrival are all based on
this system. For example: 9 a.m. is expressed as 0900, 1 p.m.
is 1300, and 10 p.m. is 2200.
Because a pilot may cross several time zones during a flight, a
standard time system has been adopted. It is called Universal
Coordinated Time (UTC) and is often referred to as Zulu
time. UTC is the time at the 0° line of longitude which passes
through Greenwich, England. All of the time zones around
the world are based on this reference. To convert to this time,
a pilot should do the following:
Eastern Standard Time ..........Add 5 hours
Central Standard Time ..........Add 6 hours
Mountain Standard Time.......Add 7 hours
Pacific Standard Time ...........Add 8 hours
For Daylight Saving Time, 1 hour should be subtracted from
the calculated times.
Measurement of Direction
By using the meridians, direction from one point to another
can be measured in degrees, in a clockwise direction from
true north. To indicate a course to be followed in flight,
draw a line on the chart from the point of departure to the
destination and measure the angle that this line forms with
a meridian. Direction is expressed in degrees, as shown by
the compass rose in Figure 16-6.
Because meridians converge toward the poles, course
measurement should be taken at a meridian near the midpoint
of the course rather than at the point of departure. The course
measured on the chart is known as the true course (TC). This
is the direction measured by reference to a meridian or true
north (TN). It is the direction of intended flight as measured
in degrees clockwise from TN.
As shown in Figure 16-7, the direction from A to B would be
a TC of 065°, whereas the return trip (called the reciprocal)
would be a TC of 245°.
Figure 16-7. Courses are determined by reference to meridians on
aeronautical charts.
Course A to B 065°
B
A Course B to A 245°
065°
245°
Figure 16-8. Magnetic meridians are in red while the lines of
longitude and latitude are in blue. From these lines of variation
(magnetic meridians), one can determine the effect of local magnetic
variations on a magnetic compass.
MN
TN
Figure 16-6. Compass rose.
36
33
30
27
24
21
18
15
12
9
6
3
NNW NNE N
E
N
E
S
E
SSE SSW
W
S
W
W
N
W
N N
E
E
S
E
S S
W
W
N
W
The true heading (TH) is the direction in which the nose of
the aircraft points during a flight when measured in degrees
clockwise from TN. Usually, it is necessary to head the
aircraft in a direction slightly different from the TC to offset
the effect of wind. Consequently, numerical value of the TH
may not correspond with that of the TC. This is discussed
more fully in subsequent sections in this chapter. For the
purpose of this discussion, assume a no-wind condition exists
under which heading and course would coincide. Thus, for
a TC of 065°, the TH would be 065°. To use the compass
accurately, however, corrections must be made for magnetic
variation and compass deviation.
Variation
Variation is the angle between TN and magnetic north (MN).
It is expressed as east variation or west variation depending
upon whether MN is to the east or west of TN.
The north magnetic pole is located close to 71° N latitude, 96°
W longitude and is about 1,300 miles from the geographic
or true north pole, as indicated in Figure 16-8. If the Earth
were uniformly magnetized, the compass needle would point
toward the magnetic pole, in which case the variation between
TN (as shown by the geographical meridians) and MN (as
shown by the magnetic meridians) could be measured at any
intersection of the meridians.
Actually, the Earth is not uniformly magnetized. In the United
States, the needle usually points in the general direction of
the magnetic pole, but it may vary in certain geographical
localities by many degrees. Consequently, the exact amount
of variation at thousands of selected locations in the United
States has been carefully determined. The amount and the
direction of variation, which change slightly from time
to time, are shown on most aeronautical charts as broken
magenta lines called isogonic lines that connect points of
equal magnetic variation. (The line connecting points at
which there is no variation between TN and MN is the agonic
line.) An isogonic chart is shown in Figure 16-9 . Minor
bends and turns in the isogonic and agonic lines are caused
by unusual geological conditions affecting magnetic forces
in these areas.
On the west coast of the United States, the compass needle
points to the east of TN; on the east coast, the compass needle
points to the west of TN.
Figure 16-9. Note the agonic line where magnetic variation is zero.
Easterly variation
Westerly variation
Agonic line
Figure 16-10. Effect of variation on the compass.
Zero
variation
N33
30
W
24
21
S 15
12
E
6
3
N33
30
W
24
21
S 15
12
E
6
3
N33
30
W
24
21
S 15
12
E
6
3
W
est
variation
East variation
NP
MP
SPSP
NP
MP
NP
MP
SP
Zero degree variation exists on the agonic line where
MN and TN coincide. This line runs roughly west of the
Great Lakes, south through Wisconsin, Illinois, western
Tennessee, and along the border of Mississippi and Alabama.
Compare Figures 16-9 and 16-10.
Because courses are measured in reference to geographical
meridians that point toward TN, and these courses are
maintained by reference to the compass that points along a
magnetic meridian in the general direction of MN, the true
direction must be converted into magnetic direction for the
purpose of flight. This conversion is made by adding or
subtracting the variation indicated by the nearest isogonic
line on the chart.
For example, a line drawn between two points on a chart
is called a TC as it is measured from TN. However, flying
this course off the magnetic compass would not provide an
accurate course between the two points due to three elements
that must be considered. The first is magnetic variation, the
second is compass deviation, and the third is wind correction.
All three must be considered for accurate navigation.
Magnetic Variation
As mentioned in the paragraph discussing variation, the
appropriate variation for the geographical location of
the flight must be considered and added or subtracted as
appropriate. If flying across an area where the variation
changes, then the values must be applied along the route of
flight appropriately. Once applied, this new course is called
the magnetic course.
Magnetic Deviation
Because each aircraft has its own internal effect upon the
onboard compass systems from its own localized magnetic
influencers, the pilot must add or subtract these influencers
based upon the direction he or she is flying. The application of
deviation (taken from a compass deviation card) compensates
the magnetic course unique to that aircraft’s compass system
(as affected by localized magnetic influencers) and it now
becomes the compass course. Therefore, the compass course,
when followed (in a no wind condition), takes the aircraft
from point A to point B even though the aircraft heading
may not match the original course line drawn on the chart.
If the variation is shown as “9° E,” this means that MN is
9° east of TN. If a TC of 360° is to be flown, 9° must be
subtracted from 360°, which results in a magnetic heading
of 351°. To fly east, a magnetic course of 081° (090° – 9°)
would be flown. To fly south, the magnetic course would be
171° (180° – 9°). To fly west, it would be 261° (270° – 9°).
To fly a TH of 060°, a magnetic course of 051° (060° – 9°)
would be flown.