According to 14 CFR part 91, cruising altitudes for VFR operations above 3,000 ft AGL are based on which course?

The correct answer is that cruising altitudes for VFR (Visual Flight Rules) operations above 3,000 feet AGL (Above Ground Level) are based on the magnetic course being flown. This regulation is set in 14 CFR part 91 and is important for maintaining safe vertical separation between aircraft flying in opposite directions.

The reasoning behind using the magnetic course is that it accounts for the Earth’s magnetic fields, which can influence navigation. When pilots determine their cruising altitudes based on the magnetic course, they ensure that the altitudes align with the rules governing the use of the airspace, thus promoting safety and efficiency in aviation operations.

In this context, the true course relates to the actual path over the earth's surface and could be affected by wind, while ground track refers to the actual path flown over the ground, which may also differ due to various external factors such as wind. On the other hand, magnetic heading indicates the direction the aircraft’s nose is pointed relative to magnetic north, which can be different from the course being followed. For these reasons, it is the magnetic course that is the standard used for determining appropriate cruising altitudes in VFR flight.