Runway 18 at an airport is oriented approximately:

Runway numbers are the magnetic heading of the runway rounded to the nearest ten degrees, with the trailing zero dropped. Runway 18 therefore points at approximately 180 degrees magnetic, meaning an aircraft landing on it is heading south. Every runway carries two numbers, one at each end, differing by 18 — so runway 18 at one end is runway 36 at the other, and which one is in use depends on the wind, since aircraft take off and land into it. For a remote pilot this is a direct planning tool: reading the runway numbers off a chart gives the approach and departure paths without needing any other information, and knowing the wind indicates which end is active. The number is magnetic rather than true, and parallel runways carry a letter suffix — L, C or R — which does not change the heading.

Runway numbers are the magnetic heading rounded to the nearest ten degrees with the trailing zero dropped, so runway 18 is oriented at approximately 180 degrees magnetic — a southerly landing direction.

Runway designations are the magnetic heading rounded to the nearest ten degrees with the final zero omitted. Each runway has two designations differing by 18, and parallel runways carry L, C or R suffixes.

Add the Zero Back. Runway 18 is 180 degrees, and 18 plus 18 is 36 — the other end.

The heading is magnetic, not true. Designations are periodically renumbered as magnetic variation drifts.

• •Reading the number as degrees without restoring the zero
• •Forgetting each runway has two designations
• •Treating the heading as true rather than magnetic