What is a key factor that can affect an aircraft's compass reading?

Magnetic variation is a significant factor that can impact an aircraft's compass reading. Magnetic variation refers to the angle difference between magnetic north (the direction a compass points) and true north (the direction along the Earth's surface towards the North Pole). This angle varies depending on geographic location and is crucial for pilots to understand, as it can lead to navigational errors if not accounted for.

When planning a flight or navigating, pilots must adjust for magnetic variation to obtain an accurate heading. Many aeronautical charts indicate magnetic variation for different regions, and this information helps pilots correct their compass readings to maintain a true course. As the aircraft changes location, the magnetic variation may also change, necessitating continuous awareness and adjustment to ensure accurate navigation.

In contrast, changes in altitude, aircraft weight, and control surface position do not directly influence the compass's magnetic properties and therefore have a lesser impact on its readings compared to magnetic variation. While these factors are essential for overall flight performance and safety, they do not affect the compass's directional accuracy relative to the Earth's magnetic field.