Definition
An error in the magnetic compass indication that occurs while the airplane is turning, particularly through northerly or southerly headings. It is caused by the magnetic dip of the Earth's field acting on the compass card when the aircraft is banked, which makes the card lag or lead the actual heading.
Plain English
When you turn the airplane, the magnetic compass briefly shows the wrong heading. The amount and direction of the error depends on which way you are turning and what heading you are passing through.
Context Anchor
Pilots encounter turning error when learning to use the magnetic compass, especially during basic instrument work and when checking heading after a turn.
Derivation
Error comes from a Latin word meaning “to wander.” That fits this aviation use: the compass reading temporarily wanders away from the airplane’s true direction while the airplane is turning.
Why Pilots Care
If a pilot rolls out of a turn the moment the compass shows the desired heading, they will usually be off — sometimes significantly. Knowing the turning error lets the pilot lead or lag the rollout to actually arrive on the correct heading, which matters most when the heading indicator has failed and the magnetic compass is the only heading reference.
Grounding Statement
A magnetic compass is most trustworthy when the airplane is steady and level, not while it is banking through a turn.
Intuition Check
Turning error does not mean the pilot made a bad turn. It means the compass indication itself is temporarily wrong because the airplane is turning.
Example Sentence 1
Because of turning error, the instructor told the student to roll out about 30 degrees before the compass showed north.
Example Sentence 2
The turning error caused the compass to lag behind the actual heading change when rolling out on south.