Sep 2012 Lesson 5.2 Navigation Earth’s Magnetism
Sep 2012Lesson 5.2
Navigation
Earth’s Magnetism
Reference
From the Ground Up
Chapter 7.2:
The Earth’s Magnetism
Pages 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 – Navigation
Aeronautical Charts
From the Ground Up
Chapter 7.4:
Aeronautical Charts
Pages 186 - 196