What occurs to the magnetic compass reading when an aircraft turns?

The correct choice highlights the phenomenon known as magnetic compass deviation during turns. When an aircraft is in a turn, the magnetic compass reading can be influenced by several factors, including the bank angle and the rate of turn. This variability occurs because the compass relies on the Earth's magnetic field, and during a turn, the magnet's alignment is affected by the centrifugal force, leading to what is often referred to as "compass error."

As the aircraft banks, especially if it is a steep turn, the turning motion can cause the compass card to lag or lead, leading to inaccurate readings. For instance, in a left turn, the compass may indicate a turn to the right due to the way the force acts upon it. The severity of the bank angle and how quickly the turn is executed will impact the amount of deviation experienced. Therefore, it is essential for pilots to be aware of this behavior to interpret the compass readings accurately during maneuvers.

In contrast, the other options suggest that the magnetic compass readings become more accurate, remain constant, or have a specific speed requirement for accuracy, which does not accurately reflect the nature of magnetic compasses in flight conditions.