Runways are named by a number between 01 and 36, which is generally the magnetic azimuth of the runway's heading in decadegrees. From what I have read, most airport runways are aligned along an East-West corridor. Why is the North-South direction rarely used?
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$\begingroup$ My guess is due to Earth's rotation, E-W winds are more common? Maybe a good question on earthscience.SE. $\endgroup$– kevinOct 18, 2017 at 13:35
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3$\begingroup$ Runways are aligned with prevailing winds so, if the observation about alignments is correct, I agree that the underlying question is more about Earth science than aviation per se. $\endgroup$– David RicherbyOct 18, 2017 at 13:37
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$\begingroup$ So if that's the case then any N-W winds would be cross winds. I'll ask this in that forum then. $\endgroup$– HuntkilOct 18, 2017 at 13:42
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3$\begingroup$ If OP would like to know why the runways are aligned the way they are like the question says, this SE is appropriate. If OP wants to learn more about why the winds blow the way they do, that is for earthscience.SE. $\endgroup$– dalearnJan 2, 2018 at 16:39
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$\begingroup$ This map shows the orientation of runways around the world: trailsofwind.figures.cc It helps give you a sense of the regional patterns. $\endgroup$– John WisemanApr 20, 2021 at 15:36
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3 Answers
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While there are many exceptions to east-west runways, generally speaking prevailing winds (which blow from a single direction) blow east-west rather than north-south. It happens because of Earth's rotation generates Coriolis effect.
There are other wind patterns besides prevailing winds. Trade winds occur near the equator and flow from either the north or south towards the equator. They curve towards the west due to the spin of the Earth. Polar easterlies blow close to the north and south poles. They blow away from the poles and curve east to west.
Hence, most of the runways are Eastish-Westish (not exactly East-West).
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5$\begingroup$ Don't these prevailing winds have more to do with solar heating patterns (and, thus, formation of Hadley cells, Ferrel cells, and polar cells ) than with the Coriolis effect? Coriolis effect does explain why cyclones and anti-cyclones form around low/high pressure centers, though. $\endgroup$– reirabOct 18, 2017 at 21:15
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Runway directions are largely chosen both for geographic land features of the site of the airport as well as the average local wind directions. As most winds blow from West to east in the continental United States, most runways will be oriented approximately in that direction. There are some sections of central Kansas and Oklahoma which have runways predominately oriented to in north south heading due to the winds blowing largely in a latitude parallel or approximately thereof in that region.
answered Oct 18, 2017 at 13:49
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$\begingroup$ Though note that the asker is in India, most of which is south of most of the continental US. $\endgroup$ Oct 18, 2017 at 13:52
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1$\begingroup$ Yeah I had to look google maps to get an idea what's he talking about. I follow NBA but still get eastern and western conference teams messed up :D $\endgroup$– HuntkilOct 18, 2017 at 13:56
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1$\begingroup$ There are also a good number of runways in the western US that are oriented north-south, because they're in valleys between mountain ranges - Reno, San Jose, and Salt Lake City are major commercial ones I can think of, plus numerous GA fields. $\endgroup$– jamesqfOct 18, 2017 at 17:59
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1$\begingroup$ "... due to the winds blowing largely in a latitude parallel or approximately thereof..." do you mean longitude / meridian? Parallels (curves of fixed latitude) run east/west while meridians (great circles of fixed longitude) run north/south. $\endgroup$– TypeIAOct 30, 2017 at 20:17
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I haven't seen the East/West bias that you reference, runways are typically built where they make the most sense. If there are prominent geological features such as mountain ranges or hills that could affect the approach, the designers may decide to construct the runway so that approaches and departures are not near the obstacles. Populated areas are another concern, if an airport is near a town, the designers may direct the departures and arrivals away from the town in order to limit the noise.
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$\begingroup$ What I meant by E-W is most of the runway bearings are 27-90 or in and around that marking but I don't remember reading about a 00-90 runway. $\endgroup$– HuntkilOct 18, 2017 at 13:40
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1$\begingroup$ Do you have citations for these claims? Obviously, there's not much you can do about geological features, but a lot of airports are old enough that keeping things quiet for the locals wasn't really considered an issue. (And one might expect the modern solution would be to build a new airport farther away from the town to avoid noise, rather than using a badly aligned runway.) $\endgroup$ Oct 18, 2017 at 13:42
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$\begingroup$ Yeah I messed up there its should be 09/27 and 18/36 as you mentioned. $\endgroup$– HuntkilOct 18, 2017 at 13:47
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$\begingroup$ @Huntkil OK -- no worries. Shame it's too late to edit your original comment. I'll delete my response but you should probably leave your reply so people don't get confused. $\endgroup$ Oct 18, 2017 at 13:49
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2$\begingroup$ @Huntkil There are lots of 18/36 (or around that) runways. They just aren't the most common orientation. The primary airports in Nashville (KBNA,) Tampa (KTPA,) Orlando (KMCO,) Seattle (KSEA,) Washington, D.C. (KIAD,) Memphis (KMEM (TN, USA, not Egypt,)) and Salt Lake City (KSLC) all have North-South orientation for their primary runways, for example. $\endgroup$– reirabOct 18, 2017 at 21:26