The Simple Secret of Runway Digits

While waiting on a plane during taxi 'till takeoff, looking out the window, you may have noticed the giant number numbering the runway, say eight, which implies seven others exist, at least, but this is a flight out of L.O.L. Airport, in Nevada's desert of nothing, there's only two runways. Which given the passenger load seems like maybe one too many already? What's the deal with runway numbers? You might wonder aloud.

Oh, hello, again. Flying to Nuuk as well, are you? It is a looong flight. So there’s tons of time for me to tell you all about runways. Let’s begin. So, before you can number a runway at an airport, you need to build the airport. And before you can build the airport, you need to plan the 'port, and what needs figuring first is which way to run the way.

Pilots want runways with winds in parallel for physics reasons that we are going to skip, both because lift physics is something people really like to argue about, [aggressively] and this isn't a physics video. Yeah, I'm recording a runway video right now, hope you don't mind. But the summary is, planes take off and land into the wind because it lets them use less runway and makes for safer and stabler landings in particular.

Now planes can land with winds unaligned but it's unsettling to watch these crosswind attempts as pilots do their best to face into the wind, while landing on a runway that does...not. Ooofff. So airports too want winds running with the runway, but the Universe is indifferent to human desires. Wind winds as it wants.

So the simple solution in aviation early days was to build a triangle of runways, put up a little wind sock, and direct the pilot to the runway that paralleled the sock and thus the wind. But, as aviation grew, so did airplanes, and thus their runways, making the triangle trick impractical for big, urban internationals. But the simple sock still solved it.

See if you record when and which way the wind sock blows and with what wind force, you've grown yourself a wind rose. A clever little dataviz tool, with the sock in the center of compass points for orientation, and bars colored and sized for strength and frequency of wind. Though it reads opposite actually of everyone’s expectations, with the lines showing the way the wind blows from and not too.

Physics stuff just loves to opposite actually. Let's just agree to avoid physics for this video, shall we? Wind roses' reverse readings aside, they reveal that in most places, most of the time, most of the wind, mostly blows back and forth in one direction, so that's surprisingly convenient. Thanks indifferent Universe! Oh, you did it for other reasons. Well still, this convenient wind happens because wind is a current of air transporting heat from where there's more to where there's less.

The earth is blasted by the nuclear heat of the sun, with the equator getting hit hot hardest, making hot air rise there, as it cools out along the edge of space, before coming back down, creating a big scale convection current, that repeats in a pattern all up and down. And because the earth is a sphere that spins, those cylindric convection currents of air on the surface, twist clockwise north of the equator and counter below. This is the Coriolis Effect.

Creating coiled currents of air everywhere, which is cool, but is also physics trying to sneak back into the video, and this isn't a physics video. All that matters is this creates the pretty stable pattern of trade winds, and if you're planning a 'port, you need only know, which way does the wind [mostly] blow.

Though at some locations, the wind rose reveals two frequent directions of wind. So, if you want to constantly and safely keep open the airport, you're going to need to run a second way. This is why many airports have an X or V layout, like LOL. They're not necessarily doing double the traffic of a one runway port, but rather, have double the chance of crosswinds when the tower will need to reroute pilots toward the other alignment for safer landings.

And once you have two of something, you need names or numbers. Sure, you could just go with Run 1 and Run 2, but pro tip, try never to use the very first thing that comes to mind without giving in a bit of a ponder first. And the wind rose reveals a better way with the compass points, which form a circle of 360 degrees. Starting at 0 North, East 90, South 180, West 270, and back to North, makes it 360 as well.

These compass degrees come from ships of the seas, because Captains and Quartermasters, when in the vast featureless nothing, could still count on their compass to point toward the North Pole, [assuming no iron hooks happened nearby] and with north as a fixed navigational point, could then communicate their heading with names broadly, East, South-east or numbers precisely, helm to 1-0-8. Quite handy.

So it's no surprise these compass headings got passed from sea ships to air ships. Thus on the wind rose devised plans for any airport the runway is already aligned with navigational numbers begging to be used, but before grabbing the obvious one, again, ponder for a moment, the runway points from the perspective of the 'port, toward the plane. The rather more important heading to use is from the planes' perspective approaching the port, which on the plan is at the opposite end actually, because it's what number matches the compass in the cockpit that's critical.

Alright, this needs a couple of example airports. Take one with a north, south runway, when the wind blows from the north to the south, the tower directs pilots to approach from the south. Meaning, they need to point the plane north, which on their compass is a heading of 360 degrees. So, let's put a big 360 on that end for now. When the winds reverse, the tower directs pilots to approach from the north, to fly south, which reads 180, so let’s put a big 180 on that end as well.

Now that we've got our heading numbers, the convention is to round them to ten and cut off the zero for the runway number. Because we don't need three sig figs of precision when airports have single digit numbers of runways, and the very stressed air traffic controllers in the tower need to repeat precisely these numbers hundreds of times a day, so saving syllables here really matters.

Thus when the tower tells the plane to use runway three six, the pilot knows they need to get south of the airport to land facing north, and while there are like, a million indicators in a cockpit, the pilot can always confirm they're doing it right by reading 360 on their ancient ancestor's compass. This low-tech check is useful as a fallback because a compass can see the way even when eyes and other equipment cannot.

As a two-runway example, an airport with a perfect ordinal X would get numbered thusly: north west to south east gives 315 for one end because that's the way the pilot needs to point and 135 at the other. Round to ten, for 320 and 140, then drop the zeros to get runways 32 and 14. On the other side, 225 and 45, round to ten again, drop the zeros for 23 and 5.

Now when the towers talk to the pilots, they say each digit individually. So, “runway two three,” because clarity here is critical, which is also why the font and exact size of these digits is standardized worldwide, though there are disagreements between the abundant aviation agencies as to if single digit runways like, 6, should have a leading zero for clarity or if that leading zero should only be in our hearts, which, it shouldn't be.

Anyway, that's the surprisingly good system behind numbering these numbers, which is always a delight to discover, unlike some other numbers I could mention. Though there are a couple of wrinkles, for, think about it, if the wind mostly blows back-and-forth in most places, then most big busy urban international airports will need multiple runways in parallel.

But parallel runways have the same heading, thus the same number under this system which would be unclear for pilots to say the least. So all the agencies assembled to agree. If you have two parallel runways, they will have the same number, but add an L or an R for left and right. If you need to construct a third runway, add a C for center too.

But with four or more, two runways will get the correct heading number, with L and R, but the others, [painfully] they’re going to get the next closest numbers, but not exactly correct numbers. Which is practical, I suppose, but also, ahhhh! It’s all slightly misaligned. [frustratingly] It’s big airports, like it d-d-doesn’t line up. Like, just try not to think about it okay, just try not to think about it.

[dings as a bell chimes] Oh! We’re landing at Nuuk already? Wow. Flights fly fast when you're flapping about flying. Time to put this knowledge to use. Our compass heading reads 42 degrees, so round to 10 for 40, cut the zero, and we'll be landing on runway zero four. And since there's only one runway at Nuuk, it'll be perfectly aligned. No doubt about that...ohhhh. It's five, not four. How embarrassing. I guess I need to delete this video now.

Hey! Why are you painting a new runway number? You do that every few decades? That must mean. Ohhhhhhh. Runway numbers depend on where the North Pole is and so, watch out! There's a geography video inside this video called, Where is the North Pole, Really? Okay, to find the North Pole, remember that the Earth is a sphere that spins.

Oh sorry, we already went over that. We draw a line about which this spin occurs, and name each end the North and South Pole. Starting with these poles, we clever humans created a square-ish coordinate system for our spherical earth, [the detailed creation of which I'm going to skip because that's a physics story for a never time that took hundreds of years and needed lots of clocks, and to make it official that London rules and Paris drools.]

But anyway! This grid is what every modern navigational system uses to get around with the GPS, global positioning, coordinates it gives. But if you were to use your GPS to direct you to the North Pole so that you could experience the planet rotating you in place, as the stars circled overhead, and you pondered the scale of the indifferent universe and your tiny, tiny existence within it, if you took out your compass to double check that the GPS got the spot right, the compass points you over the horizon toward another north pole.

What gives, compass? Well what did you expect? A compass is a magnet. And magnets follow magnetic fields, that's like their only thing. It's not a math magnet. Your magnet compass will take you to the gigantic magnetic field spewing forth from inside the earth. So there are two north poles. One for math, and one for magnets.

I mean, I guess if you want to be technical about it, there are three north poles, because the magnetic field the north pole of a magnet points to is the south pole of the earth's magnetic field, because opposites attract. But look, we're just going to ignore that, because this isn't a physics video. And there's been enough, "oh it's the opposite, actually," already, and yes, I know you can define more norths, but we're moving on.

There are two norths: math and magnet. The compass points to the magnetic north and GPS points to the geographic north, they don't have anything to do with each other, but for navigation, humans have used both, one isn't better than the other. Though, the math/geographic north is now often called True North, which feels a bit like humans picking the new one as their favorite one.

Oh, and ships of the seas have stopped using the old magnetic north, and now navigate with GPS using the true north, even modern pirates, but planes and pilots still love the traditional magnet north. And we can stop thinking about this because they’re pretty close anyway. Although…. Isn't that kind of weird just how close the unrelated poles are, on a planetary scale?

Earth just so happens to have a giant magnet that sort of, but not quite lines up with the planet's top and bottom. Indifferent Universe, are these things secretly related? And, still why would runway numbers change, just because they're pointing at the magnet one, but not the math one? Oh no, there really is an unavoidable physics video inside this geography video, and it’s called, Magnets, what's your deal?

Okay, we really can't cover everything about magnets, because it's just so much, but some bits of some metals such as iron generate around them a magnetic field. Why? and How? were a mystery for a long time until we discovered that if you take a wire and run a current of electrons through it, aka electricity, this current also generates a magnetic field around the wire.

But weirder, if you start with a current of electrons, and pop them in a magnetic field, the current will curve. And, oh look, you've stumbled upon a clue to one of the fundamental secrets of the universe. Magnets and electricity are two expressions of the same thing. Electromagnetism! That's why in science class you can coil up a wire, send a current of electricity through it, and the whole thing becomes a magnet.

One you can make stronger and stronger with each additional coil, 'cuz curving currents are magnets. Which is why when you cut the current, everything drops. Our just iron magnets are doing the same thing, but you need to zoom down and down and down and down to the atomic level to see. Here an atom of iron has a cloud of electrons, each electron with a charge, and as they whirl around they create a tiny current and a tiny magnetic field.

Zooming even closer each electron spins and this spin acts like the universe's teeny-ist-tiny-est current creating the teeny-ist-tiny-est electromagnet. Okay, look, whirl around and spin don't mean what you think down here, because in the land of quantum, [eerily] words mean nothing, there is only math, that we’re not gonna do. So. Just go with it.

Anyway, in most atoms, all these current created tiny magnetic fields arrange themselves against themselves so it all cancels out to nothing, but in a rare few atoms like iron, there happens to be an imbalance that aligns and adds up. And thus each iron atom is a tiny magnet, and if adjacent atoms align, their little magnetic fields add up, and zooming out and out and out, if all the atoms in the iron are aligned, then the iron acts as one big monkey-sized magnet, but deep down inside, it's just electron-sized electromagnets.

And scaling up and up and up and up to the whole earth's magnetic fields, it's an electromagnet all over again. See, the earth is made of parts, the thin, perilous, cool crust on which we live, the inner solid core that is several thousands of degrees hot, a middle mantle mostly solid and relatively cool, and critically, a ring of metal liquefied by the hot hot core.

And, just as on the surface do hot spots cause convection currents of air to try to even the energy out, so too does the unbelievably hot inner core cause convection currents of liquid metal. Metal that happens to be mostly iron, our magnetic friend. Thus as this mixture circles, so do all its electrons, curving currents which gets us magnet fields baby!

Though as individual coils it’s not very strong to start. To get a planet-sized field, you'd need to somehow stack the coils, [gleefully] which is where the Coriolis Effect comes back in. For just as earth's spin causes convection currents of air into coils, so too does earth spin cause convection currents of liquid metal to coil, making the fields stronger, turning the whole of the earth into a giant electromagnet.

Wow! If there's one thing the indifferent Universe loves, it's repeating the same patterns across scales and domains. Such austere efficiency. It’s beautiful. Oh get back to the runways? Ohhhhh, unlike a real electromagnet, made of stable metal, all that swirling liquid iron inside earth is not...stable.

So at any moment the field can split into multiple magnetic poles, roam randomly, or diminish entirely before, oh my, flipping north to south and south to north. Which it does every couple hundred thousand years or so, and we have no way of predicting when. Great. That’ll cause some trouble and there’s a clue that it’s coming because the strength of Earth's magnetic field has dropped 10% over the last couple of hundred years which is…concerning.

So, ah, if you're watching this video after the flip. One, take everything I said about the magnetic north and magnetic south and it's the now the opposite, actually, and, two, if it's been a couple hundred thousand years since my last upload, don't worry, that's about normal, so, be sure to smash that subscribe button, so you don't miss the next video. Oh. And hit the bell.

[begrudgingly] God, I hate that you have to do that now. Oh right, time to wrap this up. First, this giant electromagnet made of liquid metal Coriolis convecting inside earth, only semi-stably, means, earth’s magnetic field moves. That finishes with the physics and means the magnet north pole moves, and quite a lot on human time scales. When we started measuring it was safely inside of Canada, but it's recently rocketed north.

Geography over, so we can finally get back to the start. Since runway numbers are derived from the heading on a compass, when the Magnet North moves, the runway numbers need to change to match. And the closer your airport is to a magnet pole, the bigger a difference its movement makes, and thus the more frequently you need to update the number.

Which is why it's no surprise that Canada, with more northern runways than anyone, was the first to get pretty tired of frequently repainting all her northern runways and so changed her system to be based on the unmoving math north instead. But, this means when flying over her territories, pilots can't count on their compass to match the runways and the winds.

They can use their GPS, assuming the battery is charged, but, these runway numbers are inconsistent with runways in the whole rest of the world. Now Canada thinks her system is better and has created an aviation agency to try to convince all her international friends, with airports more equatorial and thus less of this problem, to try and switch with her from the old and busted Magnetic North to the new True North.

If pirates can do it, why not planes too? Well, because it's mostly a problem for you. And thus, there's not one system for numbering runways, but two. Hey guys, if you are going to switch to True North, best to get it done before the poles flip. Just sayin’.