How do you determine magnetic variation and apply it to a course?

• A. Use current aeronautical charts or navigation sources to apply variation to convert true course to magnetic course.
• B. Estimate variation from memory without charts.
• C. Variation does not require chart reference and can be ignored.
• D. Use GPS readings to determine magnetic variation.

Answer: (A)

Magnetic variation is the angle between true north and magnetic north at your location, and it’s shown on current aeronautical charts. To apply it, you convert a true course to a magnetic course by adjusting for the variation: if the variation is east, subtract that amount from the true course; if it’s west, add that amount. This rule is often remembered as “East is least, West is best.”

For example, if your true course is 90° and the chart shows 5° East variation, your magnetic course would be 85°. If the variation is 7° West, the magnetic course would be 97°. Since variation can change over time and with location, you must use the current chart or navigation source to determine the exact value.

Using memory, ignoring variation, or relying on GPS alone isn’t the correct method here. Charts provide the local variation, and GPS headings are derived from different data and may not reflect the true local variation unless a charted variation is applied.