Sep 2012Lesson 5.2

Navigation

Earth’s Magnetism

Reference

From the Ground UpChapter 7.2:The Earth’s MagnetismPages 179 - 185

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.

Outline• Earth’s Magnetism• Variation and Deviation• Conversions• Compass Errors

Earth’s Magnetism• Earth is a giant magnet

• True 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

Heading• True Heading

– Heading in relation to true north

• Magnetic Heading– Heading in relation to magnetic north

• Compass Heading– Direction that needle in compass is pointing

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

Conversions• Conversion

– 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°

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)

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

Compass Errors• Northerly Turning 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

Next Lesson

5.3 – NavigationAeronautical Charts

From the Ground UpChapter 7.4:Aeronautical ChartsPages 186 - 196