Why Flights Don't Always Travel the Shortest Route

It might seem logical that all flights should take the shortest path from one point to another to save fuel and reduce travel time. However, this is rarely the case. There are complex reasons behind the routes that pilots follow, even when these paths are not the shortest distance between two points on a map.

The Earth as an Oblate Spheroid

The Earth is not a perfect sphere but rather an oblate spheroid, meaning it is slightly flattened at the poles and bulged at the equator. This shape affects the way we understand and navigate through space. A map, being a 2D projection of this 3D shape, introduces inaccuracies. These differences become more pronounced over longer distances and larger scales, leading to discrepancies when plotting routes.

Latitude and Longitude

On a globe, the shortest path between two points is along a geodesic, which is the equivalent of a straight line on a curved surface. When projected onto a flat map, these paths appear curved. For example, the path from New York to Los Angeles looks shorter on an azimuthal equidistant projection map centered on New York, but it is actually a geodesic. The distortion increases closer to the poles, where points are more widely spaced.

Navigational Challenges

Aviation navigation is not as straightforward as it seems. Pilots need to account for the curvature of the Earth and the effects of latitude and longitude. A flight from New York to London, for instance, might require a westerly heading to compensate for the curvature of the Earth. If a navigator were to follow a true north-south path on a flat map, the plane would actually move in a spiral, never reaching its destination directly.

Pilots and Technology

Pilots rely on modern avionics technology to navigate these complex routes. GPS systems, global navigation satellite systems (GNSS), and elaborate flight management systems (FMS) are designed to handle the intricacies of geodesic paths. These systems calculate the most efficient and safest routes, often taking factors like wind patterns, airspace restrictions, and passenger comfort into account.

Crossovers and Tackles

Even with advanced technology, flights often follow routes that cross over other paths. This is because certain waypoints and air traffic control routes are fixed. For example, a flight from Chicago to Miami might need to pass over certain cities or air routes due to air traffic patterns, military operations, or weather conditions.

Magnetic Compasses and Wind Corrections

When using a magnetic compass for navigation, pilots must apply wind corrections to account for the wind direction and speed. This further complicates the process of maintaining a straight path. As wind conditions change, the airplane may need to alter its course to stay on a desired track, adding an extra layer of complexity to the navigation process.

Conclusion

While the concept of the shortest path is intuitively appealing, the practical realities of aviation navigation often require flights to take longer, more circuitous routes. This is due to the Earth's geometry, avionics limitations, and the need to account for various operational factors. Understanding these nuances can help explain why your flight takes longer than expected, even when traveling a seemingly direct route on a map.

References and Further Reading

For more in-depth information on the geodesic paths and Earth's geometry, refer to the following sources:

Carlson, R.A. (1998), Geodesic Paths on the Surface of an Oblate Ellipsoid. United States Naval Observatory Libraries nolan. U.S. Geological Survey. (2023). Ellipsoidal Coordinates. Retrieved from