What type of error is caused by a magnetic compass not indicating correctly during a turn?

The correct answer, magnetic dip error, refers to the phenomenon where the magnetic compass experiences inaccuracies in its readings when an aircraft is in a turn. This occurs due to the compass's reliance on the Earth's magnetic field, which can cause it to tilt and result in incorrect indications—especially when the aircraft is banking or changing direction.

In a turn, the magnetic forces acting on the compass can cause it to move away from the horizontal plane it's designed to operate within. This misalignment can lead to the compass pointing inaccurately, especially near the poles where the Earth's magnetic field lines are more vertical. As the aircraft's bank angle increases, the compass tends to lag behind or over-read, which is critical for pilots to understand to maintain accurate navigation.

Other options such as magnetic deviation and acceleration error involve different aspects of compass functionality—deviation refers to errors caused by local magnetic fields within the aircraft, and acceleration error relates to changes in speed affecting the compass. Heading error typically refers to errors associated with the aircraft's heading in relation to true north, not specifically tied to the characteristics of the compass during a turn. Understanding magnetic dip error helps pilots better interpret compass readings to avoid navigation errors during maneuvers.