1. “Latitude, Longitude, Earth’s Magnetism and Compass Error”
52 RCACS Ground School
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PO 404 EO 2
“Latitude, Longitude, Earth’s Magnetism and Compass Error”

2. Introduction Teaching Points Review Reference: Longitude and Lattitude
Time and Longitude
Earth’s Magnetism
Review
Reference:
FTGU Chapter 7
Section A Pages

3. Longitude and Lattitude
MERIDIANS OF LONGITUDE
Semi great circles joining the true (or geographic) poles of the earth.
They are measured from 0 to 180 degrees East and West of the PRIME MERIDIAN, which runs through Greenwich, England.
The meridian opposite the prime meridian (180) is called the INTERNATIONAL DATE LINE and here time changes a day.
Meridians are measured in degrees, minutes and seconds.
There are 60 minutes in a degree and 60 seconds in a minute.

4. Longitude and Lattitude (Cont’d)
PARALLELS OF LATITUDE
Circles on the earth's surface whose planes lie parallel to the equator.
Latitude is measured from 0 to 90 degrees North and South of the EQUATOR , which is numbered 0 degrees.
Parallels of Latitude are also expressed in degrees, minutes and seconds.

5. Time and Longitude
SOLAR DAY - interval between two successive transits of the Sun( ie. If the sun appears overhead at noon, the next time the sun appears overhead at noon, a solar day will have gone by.) A solar day is divided into 24 hours.
The sun travels once around the earth every day, so therefore it travels 360 degrees of longitude in one day. So, time can be expressed in terms of longitude.

6. Time and Longitude (Cont’d)
Time to Longitude
24 hours = 360 degrees longitude
1 hours = 15 degrees longitude
1 min = 15 minutes longitude
1 sec = 15 seconds longitude
Longitude to Time
360 degrees longitude = 24 hours
1 degree longitude = 4 min
1 minute longitude = 4 sec
1 second longitude = 1/15 sec

7. Earth’s Magnetism True North Magnetic north
The north pole of the earth.
Magnetic north
The direction the compass needle lies without considering deviation and is not at a fixed position.
The magnetic field of the earth changes as the magnetic north moves about in a circle.

8. Earth’s Magnetism (Cont’d)
Magnetic Variation
The angle between the true meridian and the magnetic meridian in which the compass needles lies, is called magnetic variation.
Also known as magnetic declination.
The technique for calculating magnetic heading is adding or subtracting the variation from the true heading.
True Heading-East Variation=Magnetic Heading
True Heading+West Variation=Magnetic Heading
Helpful Reminder
EAST IS LEAST WEST IS BEST

9. Magnetic Variation

10. Earth’s Magnetism (Cont’d)
Compass Deviation
The angle between the magnetic heading and the compass heading, which is the magnetic heading corrected for deviation.
The technique for calculating compass heading is adding or subtracting the deviation from the magnetic heading.
Magnetic Heading-East Deviation=Compass Heading
Magnetic Heading+West Deviation=Compass Heading

11. Compass Deviation

12. Earth’s Magnetism (Cont’d)
All variation and deviation can be remembered by:
T true track
V variation
M magnetic heading
D deviation
C compass heading

13. Earth’s Magnetism (Cont’d)
Compass Errors
A compass has several errors which cause the compass to not point directly to magnetic north. These errors are overcome by the following acknowledgments of the errors.
Magnetic Dip
The magnetic lines of force are parallel to the earth near the equator, but become vertical near the magnetic poles. This makes the compass needle dip toward the surface of the earth at the higher latitudes making the compass unreliable.
Northerly Turning Error
When an aircraft banks so does the compass and this causes a small error.
On turns from NORTH the compass LAGS.
On turns from SOUTH the compass LEADS.
One way to remember this is that the compass always wants to swing toward north. So when turning away it lags and when turning toward it leads.
There is no error on turns from EAST or WEST headings.

14. Magnetic Inclination (DIP)

15. Earth’s Magnetism (Cont’d)
Acceleration and Deceleration Error
When speeding up or slowing down the compass tilts and on east or west headings this tilt makes the compass turn slightly.
On east or west headings:
ACCELERATION makes the compass turn NORTH.
DECELERATION makes the compass turn SOUTH.
Helpful Reminder:
A acceleration
N north
D deceleration
S south
There is no error when accelerating or decelerating on north or south headings.

16. Questions? ?