How often should pilots check for updates on magnetic variation?

Pilots should ideally check for updates on magnetic variation monthly or during flight planning for longer journeys because magnetic variation can change over time due to shifts in the Earth's magnetic field. These shifts can affect navigation accuracy, particularly over extended distances or when flying in areas where magnetic variation is known to change significantly. Regularly checking updates ensures that pilots use the most accurate data available, which is crucial for maintaining precise navigation and safety in flight. This practice aligns well with the flight planning process, where pilots prepare for the journey, assess the route, and account for environmental factors that could impact the flight.