Runway Numbers Explained

TL;DR

Runway numbers come from compass headings rounded to the nearest 10 and divided by 10, pointing pilots toward the correct approach direction.

Key Points

• 1.Runway numbers are derived from the pilot's compass heading on approach. A plane landing facing north reads 360° on its compass, which rounds to 360, drops the zero, and becomes Runway 36 — so the number always tells the pilot which direction to fly.
• 2.Airports align runways with prevailing winds because planes take off and land most safely heading into the wind. Wind roses — compass-oriented data visualizations of wind frequency and strength — reveal that most locations have one dominant wind direction, guiding runway orientation.
• 3.Parallel runways with identical headings get L, R, and C suffixes to distinguish left, right, and center. Airports with four or more parallel runways must assign slightly incorrect heading numbers to the extra runways, which breaks the system's elegant precision.
• 4.There are two North Poles — geographic (true north, used by GPS) and magnetic (used by compasses) — and they don't align. Planes traditionally navigate using magnetic north, so runway numbers are based on compass headings pointing to the moving magnetic pole, not the fixed geographic one.
• 5.Earth's magnetic field is a giant electromagnet generated by convecting liquid iron in the outer core, shaped by the Coriolis effect. This field has weakened 10% over the last few hundred years and flips north-to-south every few hundred thousand years — its magnetic north pole is currently moving rapidly.
• 6.Canada switched its runway numbering to true (geographic) north because its northern airports require frequent repainting as the magnetic pole moves. This creates an inconsistency — Canadian runways are now numbered differently from the rest of the world, and Canada is lobbying international aviation agencies to adopt true north globally.