Plain English Meaning

The known ways a magnetic compass gives a wrong reading in flight. Pilots learn these errors so they can trust the compass when it's accurate and ignore it when it isn't.

Full Definition

The collective term for the predictable inaccuracies of a magnetic compass during flight, including variation, deviation, magnetic dip, acceleration/deceleration error, and northerly/southerly turning error. These errors arise because the compass is a free-swinging magnet aligning with the Earth's magnetic field, which is not parallel to the surface and is influenced by the aircraft's own magnetic and motion-related forces.

Context Anchor

Seen when using the magnetic compass to , , or stop a turn, especially during when are .