COMPASSES Aim • To understand the principles and considerations of compass operations. Application • Navigation flying • When DG fails Overview • Definitions • Principles – Compass Components • Considerations – Acceleration Errors – Turning Errors • Airmanship • Review Definitions • Earth’s Magnetic Field Definitions Simple Bar Magnet • a magnet freely suspended horizontally will swing so as its axis points roughly north/ south Definitions Magnetic Variation • the angular difference between the magnetic poles and true poles of the Earth. • Isogonal are lines that join places of same magnetic variation. • Agonic is the line that joins places of zero magnetic variation.
Definitions • VARIATION WEST, MAGNETIC BEST • VARIATION EAST, MAGNETIC LEAST Principles • Aircraft turns around magnet which is aligned north / south 090 270 360 180 Principles A direct reading magnetic compass is filled with a liquid which • supports its weight, • reduces friction, and • dampens oscillations Lubber line shows heading on compass card Principles Definitions • Deviation Considerations • Magnetic Dip Considerations • Minimising Dip Acceleration Errors • due to CoG displacement, • As aircraft accelerates, pivot point moves with the aircraft, but the magnet is left behind. Considerations South Accelerate North Decelerate 090 270 360 180 Considerations Westerly Apparent turn to S Apparent turn to N Southerly None None Easterly Apparent turn to S Apparent turn to N Northerly None None HDG Acceleration Error Deceleration Error Considerations • Turning Errors 340 040 340 060 040 030 330 030 310 330 Considerations • Turning Errors 200 160 200 170 160 150 210 150 190 210 Considerations Overshoot North Undershoot South Airmanship • Always avoid placing ferrous materials near the compass • Apply SAND and ONUS rules where applicable • Always apply magnetic variation when flight planning • Always apply compass deviation Review • What is an Isogonal? • What is Magnetic Dip and How do we overcome it? • Acceleration Errors • Turning Errors |