Great Circle and Rhumb Line Navigation

Great Circle Navigation

A great circle is any circle drawn on the surface of a sphere, like Earth, whose center coincides with the center of the sphere. The equator and all meridians are great circles. The shortest route between two points on the globe always follows a segment of a great circle. However, except along the equator or meridians, the track direction of a great circle route is not constant—it changes continuously as you progress, requiring regular heading adjustments.

Great circle routes are especially advantageous for long-haul flights and high-latitude operations, where the distance savings compared to a rhumb line can be significant. For example, a great circle route from New York to Hong Kong over the pole is dramatically shorter than the equivalent rhumb line.

Rhumb Line Navigation

A rhumb line (loxodrome) is a path crossing all meridians at the same angle, meaning it maintains a constant true bearing. All parallels of latitude, including the equator, and all meridians are rhumb lines. However, only the equator is both a rhumb line and a great circle; all other parallels are small circles.

Rhumb line navigation is simpler for aircraft without advanced navigation systems, as it allows the pilot to maintain a steady heading. This simplicity comes at a cost: except along the equator or meridians, a rhumb line is always longer than the corresponding great circle route. The difference in distance increases with greater changes in longitude and at higher latitudes.

Difference Between Great Circle and Rhumb Line

• Great circle: shortest distance, changing track
• Rhumb line: constant direction, longer distance (except equator/meridians)
• The divergence between the two routes grows with latitude and longitude difference

Practical Application

For short distances or low latitudes, the difference between great circle and rhumb line is minimal. Over longer distances or at higher latitudes, using a great circle can save significant time and fuel. On charts, great circles appear as curves (except on certain projections), while rhumb lines plot as straight lines on a Mercator chart.