If one end of a runway is numbered 09, what number designates the opposite end of the same runway?

Runway numbers are based on the magnetic compass heading that the runway is aligned with. Each runway is given a number that corresponds to the closest ten-degree increment of its heading, with the number rounding to the nearest whole number.

In this situation, a runway numbered 09 indicates that it is oriented closest to a magnetic heading of 90 degrees. To find the number for the opposite end of the runway, you add 180 degrees to the heading. Since 90 degrees plus 180 degrees equals 270 degrees, this means the opposite end of the runway would be numbered 27.

This alignment and numbering system serves a practical purpose, providing pilots with critical information and orientation as they approach and navigate runways. The proper identification of each runway's orientation plays an essential role in aviation safety and efficiency.