Definition
Any inaccuracy in the indication of a magnetic compass caused by influences other than the Earth's magnetic field, including variation, deviation, magnetic dip, oscillation, and acceleration/turning errors. These errors cause the compass to display a heading that differs from the aircraft's actual magnetic or true heading.
Plain English
The difference between what the compass shows and the heading the aircraft is actually flying. Several known factors cause the compass to read slightly wrong, and the pilot must account for them.
Context Anchor
Seen when learning magnetic compass errors, especially deviation and the compass correction card used in the cockpit.
Derivation
Compass comes from an older word meaning to go around or measure around, which fits an instrument that shows direction around a full circle. Error comes from a word meaning to wander or stray, which helps here because the compass indication has strayed away from the correct direction.
Why Pilots Care
Uncorrected compass error leads to inaccurate headings, navigation mistakes, and potential loss of situational awareness, especially during partial-panel instrument flight.
Intuition Check
Compass error does not mean the pilot made a mistake. It means the compass indication itself differs from the correct direction by a measurable number of degrees.
Example Sentence 1
Before takeoff, the pilot checked the compass correction card to account for compass error caused by metal and electrical equipment in the cockpit.
Example Sentence 2
During the instrument scan the student noted a five-degree compass error and adjusted the heading indicator accordingly.