Why Nautical Miles Used By Airplanes

On the roads, the odometer tracks meters, while the speedometer shows kilometers per hour (km/h). However, measuring distance in the air or on water is a bit trickier. That’s where nautical miles come into play, a unit of length specifically created for navigation in air, sea, and space.

The nautical mile is rooted in geography, history, and practicality. It’s equivalent to 1.852 km (or 1.851853 km according to international standards) and was established in 1929 by the International Hydrographic Organization (IHO).

Although both units are related to the size of the Earth, the meter (which is 1/10,000,000 of the Earth’s meridian) is more suited for land measurements and doesn’t have a direct connection to latitude and longitude. The nautical mile isn’t included in the International System of Units (SI).

Sailors have been using nautical miles for centuries to navigate vast ocean distances. Especially when European explorers began extensive global navigation in the 16th century, it was super convenient for them to understand that the distance a ship traveled over the sea along a longitudinal meridian directly related to the degrees of latitude crossed by the ship.

Since latitudes are evenly spaced across the Earth’s surface, with a total of 180 degrees from the North Pole to the South Pole, this calculation indicates that one nautical mile is equal to 1/(180*60)th of the distance along a meridian from the North to the South Pole.

This also assumes the Earth is a sphere, which closely resembles its actual shape as an oblate spheroid. This definition of a nautical mile, derived from the distance between two degrees of latitude, makes it a practical unit for navigation, benefiting both sailors and pilots, and allows them to easily and accurately determine the latitude of a location.

If a plane is flying from Point A at Latitude 35° N, Longitude 118° W, to Point B at Latitude 38° N, Longitude 120° W.

Latitude Difference: 38° – 35° = 3°

Convert to Minutes: 3° * 60 minutes/degree = 180 minutes

Nautical Miles: 180 minutes * 1 nautical mile/minute = 180 nautical miles (approximately)

Kilometers: 1 nautical mile = 1.852 kilometers = 180 * 1.852 = 333 km

One nautical mile is equivalent to one minute of latitude, which enables pilots to chart their routes accurately and navigate smoothly. This standardization aids in keeping on course with maps, guarantees safer flights, and enhances GPS-based navigation.

A nautical mile is better suited for navigating over water, where the surface can change constantly, compared to ground-based measurements like kilometers and miles.

Using nautical miles also simplifies flight planning and enhances international cooperation in aviation.

If the global adoption of the metric system continues to grow as it has in the United States, we might see kilometers becoming more common in daily life. However, in the fields of navigation and aviation, nautical miles will remain the standard.

DISCLAIMER: This article is derived from information available in the public domain.