Magnetic Dip and Compass Acceleration Error

Magnetic Dip Explained

Magnetic dip, also called magnetic inclination, is the angle between the horizontal plane and Earth's magnetic field lines. At the magnetic equator, the field is horizontal (zero dip), but as you move toward the poles, the field lines tilt more steeply, reaching 90° at the magnetic poles. This inclination causes the compass needle to want to tilt downward (in the Northern Hemisphere) or upward (in the Southern Hemisphere), but the compass is physically balanced to remain level.

Compass Acceleration Error

When an aircraft accelerates or decelerates on an east or west heading, the force of acceleration combines with magnetic dip. In the Northern Hemisphere, accelerating on an east or west heading causes the compass to indicate a turn toward the north (Acceleration North Deceleration South—'ANDS'). Deceleration causes a false turn toward the south. This error is most pronounced at higher latitudes where dip is greater and is negligible at the magnetic equator where dip is zero.

Operational Implications

These errors mean that pilots must interpret compass readings with caution during acceleration, deceleration, and turns, especially during takeoff, climb, and level-off. Understanding when and why these errors occur is essential for accurate navigation and safe aircraft operation.