T H E P R I VAT E P I L O T L E A R N I N G G U I D E
CROSS-COUNTRY FLIGHT
LATITUDE AND LONGITUDE
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Position can be expressed in terms of latitude and longitude. This coordinate system is displayed
as a grid superimposed onto all VFR navigation charts, providing a ready means of identifying
a precise position anywhere on the globe.
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The grid originates at the intersection of the Equator and the
Prime Meridian, dividing the Earth into four hemispheres: Northern,
Southern, Eastern and Western. The lines that run east and west,
parallel to the equator, are called lines (or parallels) of latitude. The
equator is the zero-degree reference for measuring degrees to the
north and south. The angular distance from the equator to either pole
is 90 degrees; lines of latitude measure this distance from 0 – 90
degrees north and south.
The vertical lines that originate at the north and south poles, and
cross at right angles to the equator, are lines of longitude, also known
as meridians. The zero-degree reference for longitude is the Prime
Meridian, which passes through the town of Greenwich, England. This
is the reference for measuring degrees of longitude (from 0 – 180
degrees) east and west.
Each degree is divided into 60 equal parts called ‘minutes’; minutes
are further broken down into ‘seconds’ (which are not depicted on
VFR charts). Aeronautical charts depict lines of latitude and longitude
spaced at 30-minute intervals. When giving a position using latitude
and longitude coordinates, the latitude measurement is always given
first. When using minutes for a given position, the degree value
comes first. A typical coordinate set would be written and read as
follows: N43°46’ – W89°38’; Forty-three degrees, forty-six minutes
north; eighty-nine degrees, thirty-eight minutes west.
Note: As the United States is located in the northwestern hemisphere
of the globe, the coordinate sets you will encounter in this country will
always be North and West.
Plotting coordinates is much easier than it sounds. To start, open
up any sectional and identify the lines of latitude and longitude.
They appear as thin black lines interspersed with hatch-marks. The
horizontal lines are latitude, the vertical are longitude—each small
hatch-mark is one minute.
Look at the points where the vertical and horizontal lines intersect
and you will see several points with black numbers. The numbers are
degrees, and are aligned with their respective lines, i.e. numbers read
horizontally are latitude, and the vertical are longitude.
You will notice that some lines have no numbers associated with
them. These are the half-degree points; only whole degree numbers
are printed on the chart. Recall that latitude and longitude lines are
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spaced 30 minutes apart; instead of reading a point as being at 90
and a half degrees, it would be 90 degrees, 30 minutes; 71 and a
quarter degrees is actually 71 degrees, 15 minutes, etc.
DIRECTION
When determining direction, always reference your orientation from
north. When it comes to navigation there are actually two “norths” to
consider. True north is the geographic north pole of the Earth and the
point where lines of longitude originate. Magnetic north is the place
where the magnetic field surrounding the earth passes through, and
where the magnetic compass in your airplane will point. Magnetic
north is located close to N71° – W96°, which is roughly 1,300 miles
from geographic north!
Due to the rotation of the Earth, the time of day is different at
different places on the globe; time zones reduce confusion caused
by these differences. Time zones typically encompass 15 degrees of
longitude, making the time difference between each zone one hour.
There are four time zones in the continental US: Eastern, Central,
Mountain and Pacific. A pilot planning a flight that begins in one time
zone and ends in another must take this difference into account. This
is especially true if a pilot is not night current and crossing a time
zone may result in night flight.
Because a pilot may cross several time zones during a flight, a
standard system of expressing time has been developed. It is called
Coordinated Universal Time (UTC), sometimes referred to as ‘Zulu’
time. UTC is the time at the zero-degree line of longitude (Prime
Meridian). All of the world’s time zones are based on this reference,
and time given in UTC is usually appended with a ‘Z.’
The conversions to UTC for the United States are as follows:
• Eastern Standard Time + 5 hours = UTC
• Central Standard Time + 6 hours = UTC
• Mountain Standard Time + 7 hours = UTC
• Pacific Standard Time + 8 hours = UTC
During Daylight Savings Time (DST), subtract one hour from UTC.
Nearly everything concerning time in aviation is expressed in UTC:
ATC instructions, weather reports and forecasts, estimated times for
arrival and departure, etc. As an example of how UTC standardizes
time, consider this: 1400 Eastern Standard Time, 1300 Central
Time and 1100 Pacific all occur at 1900Z.
TIME
The last navigation variable is time. In aviation operations, a 24hour clock is used; this eliminates the need to distinguish between
A.M. and P.M. Time prior to noon is expressed in hundreds, with the
single-digit hours preceded by zero. For example, 4:00am is 0400;
10:30am is 1030. To convert afternoon time, simply add 12 to any
hour past noon; 1:00pm becomes 1300; 6:00pm is now 1800;
8:45pm is 2045, etc.
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Note: The colon separating hours and minutes is dropped for time expressed
on a 24-hour clock.
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