When planning a cross-country trip and observing an isogonic line labeled 13°E, what magnetic heading should you fly if your true course is plotted at 263°?

To determine the correct magnetic heading to fly, you need to adjust your true course based on the magnetic variation indicated by the isogonic line, which in this case is 13°E. The true course is the direction you plan to fly over the ground, measured in degrees True (T). Since the isogonic line indicates a magnetic variation of 13° East, you need to convert your true course to a magnetic heading by subtracting the variation.

Starting with the true course of 263°, you would subtract the 13° of east variation:

263° (True Course)

• 13° (Magnetic Variation)

= 250° (Magnetic Heading)

This means that to maintain a course of 263° true, you should fly a magnetic heading of 250°. The option selected reflects the necessary calculation of subtracting the east variation from the true course to arrive at the appropriate magnetic heading for navigation.