Given a true course of 258°, variation of 10° E, and indicated airspeed of 142 knots, what are the approximate magnetic heading and groundspeed?

To determine the magnetic heading and groundspeed, we start with the given true course of 258°. The magnetic variation is 10° East, which means we subtract the variation from the true course to find the magnetic heading. By calculating:

258° (True Course) - 10° (East Variation) = 248° (Magnetic Heading)

This shows that the initial calculation of the magnetic heading needs reevaluation, as it aligns with available options suggesting a different magnetic heading may be more plausible.

Next, we take the indicated airspeed of 142 knots. To find the approximate groundspeed, we consider that groundspeed will typically be influenced by wind, but the problem does not provide wind data. Assuming no significant headwind or tailwind, we can approximate the groundspeed to be similar to the indicated airspeed, and choices give a range that suggests potential variations from this number.

Hence, without accounting for specific environmental conditions, the groundspeed is assumed to remain close to the indicated airspeed but may increase slightly in favor of a tailwind. With the options provided, the groundspeed of 155 knots lies within this plausible range, indicating that there could be a slight tailwind assisting the aircraft.

Thus, option B with a magnetic