Magnetic Compass: Review

MAGNETIC COMPASS REVIEW

PRINCIPLES • The earth is a huge magnet. • Any freely suspended magnet will align itself with the earth’s magnetic poles. • The compass is a self-contained unit requiring no external power source.

INHERENT ERRORS • Magnetic poles differ from the earth’s true poles, due to variation caused by minerals in the earth’s crust. • Isogonic lines connect points of equal variation. • WEST IS BEST 030°T+10°var.=040°M • EAST IS LEAST 030°T-15°var.=015°M

Deviation • Deviation results from aircraft magnetic fields affecting compass alignment with magnetic north. • Correction is achieved by swinging the compass, and applying a compass correction card for specific equipment conditions.

Dip • Dip error results as the compass card dips toward the surface of the earth. • The earths magnetic field is parallel to the earths surface at the magnetic equator but dips towards the poles. • If a magnetic compass is anywhere other than the magnetic equator it tends to dip towards the earth to follow the magnetic field.

Northerly Turning (Dip) Error • The earth’s magnetic field causes the compass to dip to the low side of the turn. • Error is most pronounced turning through north and south. • In the Northern Hemisphere: Lag North, Lead South.

LAG NORTH

LEAD SOUTH

Acceleration/Deceleration Error • Acceleration error occurs during airspeed changes. • It results from inertia and magnetic dip. • Most pronounced on headings of east and west. • ANDS – accelerate north, decelerate south.

ANDS