How should pilots use a heading indicator regarding magnetic variation?

The correct choice emphasizes that pilots must ensure their heading accounts for magnetic variation when using a heading indicator. Magnetic variation is the difference between true north (the direction of the North Pole) and magnetic north (the direction indicated by a magnetic compass). Since the heading indicator typically reflects magnetic heading, pilots need to adjust for magnetic variation to navigate accurately.

In practical terms, this means that pilots should be aware of the local magnetic variation and adjust their headings accordingly to maintain a true course. Failure to do so could result in navigational errors, potentially leading to deviations from the intended flight path. By accounting for magnetic variation, pilots enhance their situational awareness and improve overall navigational accuracy during flight operations.