1. Navigation Earth’s Magnetism

2. Reference
From the Ground Up Chapter 7.2: The Earth’s Magnetism Pages

3. Introduction
Most navigation is based on the Earth’s magnetic field. Compasses use the field to determine where north and south are.
Pilots need to know how to use a compass and how to use it with a map to be able to properly plan a flight.

4. Outline Earth’s Magnetism Variation and Deviation Conversions
Compass Errors

5. Earth’s Magnetism Earth is a giant magnet True North Magnetic North
Direction towards geographic north pole
Magnetic North
Direction compass will point (not considering compass deviation)
Magnetic north pole is not in a fixed position, changes over years, it roughly orbits around true north

6. Heading True Heading Magnetic Heading Compass Heading
Heading in relation to true north
Magnetic Heading
Heading in relation to magnetic north
Compass Heading
Direction that needle in compass is pointing

7. Variation and Deviation
Variation (AKA Magnetic Declination)
Angle between true heading and magnetic heading (or true meridian/north and magnetic meridian/north)
Deviation
Angle between compass heading and magnetic heading
Caused by magnetic fields generated from metal and electronics in aircraft

8. Conversions Conversion West is best (+), East is least (-) Examples:
True Heading + Variation = Magnetic Heading + Deviation = Compass Heading
West is best (+), East is least (-)
Examples:
TH 100° + V 11°W = MH 111°
MH 180° + D 10°E = CH 170°
CH 200° - D 20°W = MH 180°

9. Isogonic Lines Lines on a map joining places of equal variation
AKA Isogonals
Numbered as degrees east or west of true north (example: 11° W)
Agonic Lines are lines on a map joining places of zero variation (0° Isogonals)

10. Compass Errors
Compass most accurate when flying straight and level; Heading Indicator should normally be used
Deviation
Caused by magnetic fields generated from metal and electronics in aircraft
Can cause compass to be several degrees off
Magnetic Dip
Earth’s magnetic lines become vertical near north and south poles
Cause compass to start trying to point towards ground

11. Compass Errors Northerly Turning Error Acceleration Error
Compass misreads during banked attitudes
Most apparent on north or south headings
On turns from the north, compass lags
On turns from the south, compass leads
Acceleration Error
Acceleration causes small turning moment in compass
Most apparent on east or west headings
Acceleration causes compass to show small turn to north
Deceleration causes compass to show small turn to south

12. Next Lesson
5.3 – Navigation Aeronautical Charts From the Ground Up Chapter 7.4: Pages