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Why is it called runway 27L?

The tidy logic behind runway names — headings, parallels, and the wind.

Runway names look cryptic until you learn the one rule behind them: a runway is named for its magnetic heading, rounded to the nearest ten degrees, with the zero dropped. A strip aligned 274° magnetic rounds to 270, so landing in that direction it is runway 27. Land the opposite way on the very same concrete and you are heading 094° → rounded 090 → runway 09. Every runway therefore has two names exactly 18 apart — 09/27, 13/31, 04/22.

L, C and R

When airports build parallel runways they share the same number, so a suffix separates them: Left, Right, and Centre for a third. Which is "left" depends on the direction you are facing, which is why the same physical pavement is 27L from one end and 09R from the other. Airports with more than three parallels cheat the numbers: Los Angeles calls its southern pair 25L/25R and the northern pair 24L/24R even though they are all essentially aligned — a deliberate one-digit offset to keep names unique.

Runways get renamed

Because the names follow magnetic heading and the magnetic north pole drifts, runway numbers are not forever. When accumulated magnetic variation tips a runway across a rounding boundary, the airport repaints the numbers, reprints the charts and re-records the ATIS. It happens constantly around the world — a runway built as 17/35 can spend a decade as 18/36. Aviation accepts this administrative churn because the payoff is operational: a pilot cleared to land runway 27 knows the final approach course is about 270° before looking at a single chart.

The wind picks the runway

Aircraft take off and land into the wind — a headwind lowers the ground speed needed to fly, shortening the run and steepening the climb. So the "runway in use" is simply the end pointing closest into today's wind: wind from 300° favours runway 31; swing the wind to 130° and the airport turns around. Crosswinds have hard limits, which is why many airports keep a second runway at a crossing angle — Bratislava's 13/31 and 04/22 in this simulator are a classic example, and picking between them as the wind shifts is part of the job.

In the simulator

The ATC Radar Simulator applies all of this: every runway end is named by its real designator and the localizer course is derived from the number. The simulator flies in calm air, so you choose the runway in use yourself in the session dialog — the HUD's RWY readout shows it — and the airport pages list each field's real runway pairs.