Monday, August 18, 2014

Apple #681: Airport Runway Signs

I have had a request!  Daily Apple reader Jamarcus wants to know, what do all those signs next to airport runways mean?  You know, the ones that look something like this:

This sign lights up so it will be visible to pilots at night. But what do the letters and numbers mean?
(Photo and sign from Astronics Corporation)

A very good question.  Something I have often wondered myself.

Before you can interpret the signs, it helps to know how things get named at airports.


  • There are taxiways, and there are runways.  Runways are the paved strips where planes take off and land.  Taxiways are the paved passageways the planes take to get from the terminal to the runway to take off, or from the runway where they've landed back to the terminal.
  • You definitely want to keep the two separate because you don't want one plane ambling down a runway as another plane is about to land there.
  • A lot more real estate is covered by taxiways.  Some of our airports are enormous, and a plane may have to travel quite a long way to get from the terminal gate out to the runway.  It will have to drive down a lot of taxiways before it gets to the runway.
  • Taxiways are indicated with letters, beginning A, B, C, etc.  All airports begin their naming of taxiways with A, and one taxiway can go for a really long way. So the signs you see from your airport window will most often have an A on them.  
  • Some airports are so big or have so many taxiways, they get up to G.  Theoretically, taxiways could be lettered all the way up to Z, and then get the letters doubled: AA, BB, CC, etc.  But in real life, it's rare that taxiways are named much deeper into the alphabet than G.
  • Taxiways can never be named H.  The letter H is reserved for helipads -- landing places for helicopters.
  • They can also never be named I or O, because those letters could be mistaken for numbers.
  • They can also never be named X because an X on a sign means the runway or taxiway is closed.
  • You will often see signs that combine a letter and a number, such as A1, or B3 (as above), or C2.  These indicate either:
    • a stub taxiway -- a connector that goes from a runway to a taxiway that runs parallel to the runway (a little cross-bar connector from a runway to a taxiway) 
    • or the exit or entrance connector that goes from a taxiway to & from the terminal. The connectors get named sequentially A1, A2, A3, etc. along the length of the taxiway.
  • Keeping all those rules in mind (and a few I've left out for brevity's sake), an airport also needs to make sure no taxiway has a name that could be confused with a runway, and no two taxiways have the same name. 

Well, this is hard to see. But the runways have the dashed lines, and the taxiways are thinner.  The taxiways are named, from top to bottom, A, B, and C, and the little connectors that go between the runways and the taxiways are named, from left to right, A1, A2, A3, A4, A5, A6, and A7, and then in similar fashion for the connectors that go off taxiways B and C.  The little taxiway that goes vertically, bisecting the runways and the parallel taxiways, is named J.  That one gets its own letter, as opposed to something like C5, because that's a high-traffic taxiway.
(Diagram from the FAA's Engineering Brief on Taxiway Nomenclature)

This isn't a real-life runway but a screen shot from a simulator, but it does the job for our purposes.  The runway is on the right, as indicated by the white markings. The taxiway, outlined in yellow, is on the left.  A taxiway stub connects the two.  The colored paint and types of markings is a whole other set of visual indicators for pilots.  
(Photo from SimFlight)

  • By the way, the names of taxiways are not pronounced as the letters (A, B, C), but by the names that correspond to each letter, according to the NATO phonetic alphabet (Alpha, Bravo, Charlie).   So taxiway A2 would be called "Alpha two."
  • Yes, this is the same alphabet popularized by Wilco's Yankee Hotel Foxtrot.


  • Runways get named using numbers.  The thing that determines which numbers get assigned to a runway is where the runway is relative to points on a compass.  Then it gets turned into a kind of code.
  • North, South, East, and West all correspond to degrees on a compass.  North = 360°, for example.  According to this runway code, you lop off the 3rd digit of the compass point.  So if a runway were pointing true north, it would get numbered 36.  For the 4 points of the compass, the code works like this:
    • North = 360° = runway number 36
    • South = 180° = runway number 18
    • East = 90° = runway number 9
    • West = 270° = runway number 27
  • But of course it's rare for a runway to be heading in exactly the position of one of the points of the compass.  So in most cases, the runway number is arrived at by rounding off ±5°.  Let's say a runway is heading 176°.  That's within 5° of 180°, so its runway number would be 18.
  • It is also of course likely that a runway won't fall within 5° of one of the ordinal points on a compass, so it is very likely that runways will be named other numbers besides these four.
  • Because there are only 360° on a compass, you can't have a runway with a number higher than 36.  Also, since North is indicated by 360°, there is no 0°, so there will be no runway named 0.
  • Finally, because you may be allowed to land on a runway from either direction, its name will often be expressed from either approach direction, as in ##-##.  The first number indicates the compass direction from one end of the runway, let's say, 22.  That means the runway's compass heading is 220° (or within ±5° of that).  So the second number will be 180° from 220°, which is 40°, which becomes number 40.  This runway's official name is therefore 22-40.
  • By the way, the runway numbers are not pronounced the way we normally pronounce two-digit numbers. They are said individually.  Not "runway twenty-two" but rather "runway two-two." Nine is pronounced "niner."  Yes, just like in Airplane!


  • Now that you know what the letters and numbers mean, let's look at some signs.

(Photo and sign from Astronics Corporation)

  • This is our sign from earlier.  Now we know that B means "Taxiway Bravo" and B3 indicates a taxiway stub or connector or exit.  Anything in a black box with a yellow outline means "this is where you are."  So this sign means "You are on Taxiway Bravo. Taxiway stub Bravo three is to the right."

(Photo and sign from Astronics Corporation)
  • Here's another one. This means "You are on Taxiway Alpha.  Taxiway Foxtrot is to the left or angled to the right."

(Image from Avery Dennison)

  • Let's try a little more complicated one.  This one means, You are on Taxiway Hotel 3, Taxiway Charlie is to the left, Taxiway stub Charlie two is angled to the upper right, and more of Taxiway Charlie is to the right.
  • The red circle with the white line through it means "CLOSED."  This sign seems to be saying a little too softly that Taxiway stub Charlie two is closed, but that's what it means.  
  • (I think in this case, Avery Dennison, a label-making company, is saying you could put one of our  temporary "CLOSED" sticker on your runway signs.  Really, the airport should put up a giant CLOSED sign and they're also supposed to paint big red Xs on the ground before a closed section.)

This is what a CLOSED, or NO-ENTRY sign should look like. Either this or a gigantic X. Big and obvious. No subtlety. 
(Image from the Aircraft Owners and Pilots Association

  • Those yellow signs are the kinds you see most often. Taxiway Alpha's exit is this way, etc.  Now that you've got those down, you'll be able to interpret most of the signs along the taxiways that you'll see from your airplane window.
  • But there may be other signs in other colors and letters.  What about those?

(Image from Holland Aviation)

  • By now you know the part in the black box means "You are currently on Taxiway stub Sierra six."  The stuff on the right you might guess indicates a runway named either "two four or zero six." You are correct about that, but since it's in red, it also means a whole other thing.
  • Red signs mean "stop" or "holding position."  This means the plane has to stop right here and wait until it gets the go-ahead from air traffic control to proceed onto the runway.  There will also be some yellow & black markings like crazy on the pavement next to the sign.  The plane is absolutely not to cross those yellow and black lines at all until the pilot gets the OK.

(Photo from Airchive)

  • What about this one?  It's a red sign, so you know it means stop, but there are no numbers on it, only the letters ILS.  That can't mean a taxiway, right?
  • Right.  ILS stands for Instrument Landing System.  This is the signalling system used by air traffic control to give pilots precise information about taking off from a runway, or landing on it.  The red ILS sign means this is a critical ILS zone, and "stop here and wait or you will interfere with ILS signals being given to planes taking off or landing on this runway."

(Image from the Aircraft Owners and Pilots Association)  

  • You might also see a red sign with two runway numbers followed by the letters APCH.  That stands for "Approach."  Like the ILS sign, this means you've entered the approach for a particular runway (runway 15, in this case), and you must wait here so you don't interfere with the ILS signals for incoming planes.

(Photo from Air News Times)

  • This image is kind of dark, but anyway, what does FBO mean?  That's not a taxiway either, right?
  • Right.  FBO means "Fixed-base operator."  It's basically the gas station for airplanes.  FBOs are typically businesses that operate independently of the airport -- Chevron, or Philips 66, or some other gas company -- but that serve airplanes at the airport.  They provide fuel for the planes, and they also may provide maintenance services, hangars, parking, equipment rental, and so on.  They are used most often by people who fly their own planes.

(Image from the Aircraft Owners and Pilots Association

  • This one you don't see very often, but MIL means a military installation is that way.
  • I think that about covers it.  Thank you for flying with the Daily Apple today.  Enjoy your destination.

FAA, Airport Marking Aids and Signs
FAA Engineering Brief No. 89, Taxiway Nomenclature Convention
Jim Sweeney, The Short Course: Airport Signs
Aircraft Owners and Pilots Association, Airport Signs and Markings
Nevada DOT, AOPA's Airports Signage & Markings (this uses the terms runways and taxiways interchangeably, which is very confusing)
AOPA's runway flash cards
Bangalore Aviation, Airport runways: All you wanted to know but were afraid to ask
Sploid on Gizmodo, This is what all the signs and symbols at the airport runway mean
Alpha Bravo

1 comment:

  1. In the Taxiways section you said that taxiways can't be labeled "H," but later in the Signs section you have a picture saying "H3" and you said it means Taxiway Hotel 3. What gives?


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