Which unit is not commonly used for aeronautical distances?

The nautical mile is the standard unit for measuring distances in aviation because it is directly related to the Earth's geometry. One nautical mile corresponds to one minute of latitude. This makes it particularly useful for navigation over the curved surface of the Earth, allowing pilots to calculate distances and positions more accurately.

Statute miles are commonly used in land-based measurements but are not standard in aviation. The foot is typically used for altitude measurements rather than horizontal distances, so it doesn't serve the purpose of measuring flight distances directly.

While kilometers are recognized and can be used in some international operations, they are not the prevalent standard in aeronautical applications in many countries, particularly the United States. This makes kilometers less commonly used for aeronautical distances compared to nautical miles and statute miles. Thus, it is more appropriate to consider kilometers as the unit that is not commonly used for aeronautical distances in general aviation contexts.