Why is preflight planning critical in accounting for magnetic variation?

Preflight planning is essential for accurately accounting for magnetic variation because it ensures pilots adjust their compass headings in accordance with the differences between true north and magnetic north. Magnetic variation, also referred to as magnetic declination, varies by geographic location and can significantly impact a pilot's navigation.

In the context of aviation, the magnetic compass is sensitive to this variation, and if not properly accounted for, pilots risk navigating off course, which can lead to dangerous situations. During preflight planning, pilots assess the magnetic variation specific to their flight route and make necessary adjustments to their headings to ensure they stay on track. By incorporating corrections for magnetic variation, pilots enhance the accuracy of their navigation, which is crucial for both safety and efficiency in aviation operations.

The other options, while they may contribute to overall flight efficiency or safety in different ways, do not specifically address the critical aspect of adjusting headings based on magnetic variation. Hence, they do not capture the core importance of preflight planning in this particular context.