For most of us, the sight of blue lights and yellow lines outside an aeroplane's window is the cue to turn our phones back on. For pilots, it's more like a secret language -- a language that is vitally important to safety and, increasingly, embedded with emerging technology.
I was very recently on a plane circling over LGA when I realised I had no idea what any of the patterns, colours, or letters on the runway really meant. Take the lighting, for example. In Dubai this month, Honeywell finished up installing what it describes as the very first all-LED runway lighting system; like the rest of the world, airports are giving up their inefficient lightbulbs. Meanwhile, I -- the average clueless and/or terrified passenger -- couldn't tell you whether a light on the runway was LED or incandescent.
I wanted to know more about the mysterious language. A Wired article from last year gave a few hints, along with the amazing Tumblr Holding Pattern. And it turns out that the Federal Aviation Administration keeps public guidelines for all of these design elements online. After digging into the FAA's list of documents and exploring in Google Earth, this is what I found.
As a passenger, it feels like most pilots try to come down as close to the edge of whatever seems to constitute runway as possible. That's definitely not the case -- there's a language of lines and indicators that helps pilots time their touch-down at the exact right moment. Most runways at major airports follows the same pattern, defined by the FAA's advisories on runway markings, found right here as a PDF.
First, there's something called the blast pad: A patch of what looks like runway, painted with yellow chevrons or lines, that's actually often not strong enough to hold the weight of the plane ("Your gear may poke through the runway!" exclaims one virtual training primer). It's never driven or landed on, but it still serves an important purpose, since it's designed to prevent the "blast" of departing jets on the runway from creating bare or eroded patches on the soil just before the runway. Basically, it's a runway band-aid, as you can see here at LGA:
Landing on the blast pad (which might cave below the weight of a plane) is what the primer calls a "catastrophic error". The runway proper begins with the threshold. This is just what it sounds like -- a number of thin, long lines that are used to indicate the width of the runway.
Above it, you'll see the runway number and often a letter: Runway names are determined by the "nearest one‐tenth the magnetic azimuth of the centreline of the runway," says the FAA. Since there are only 360 degrees, runway numbers will only ever go up to 36. What about the letter? Well, the letter is added if there are two (or more) runways parallel to each other, to differentiate from the degree name. For example, here are three parallel runways at Midway in Chicago:
So we've got four different types of markings already -- all of which aren't intended to actually be landed on. So where does the plane touch down? That would be somewhere that looks fair inconspicuous, compared to everything around it: The six lines after the runway number.
Which leaves one remaining question: What the hell are those thicker white rectangles on every runway, like the ones seen here in Tokyo?
Those are actually visual aides for pilots. They're called the "aiming points", and they're what the pilots are supposed to be looking at when coming in for a landing.
The Numbers, Colours and Signs
So, who decides on a typeface? Again, that would be the FAA. All letters and numbers have to adhere to its careful guidelines, which include everything from the carefully-proportioned dimensions of the characters to the "1" with a horizontal tip to avoid confusion. All characters have to be 60 feet (18.29m) high, except 6 and 9 -- which can be 3 feet higher because of the tails:
Another thing to keep an eye out for? Markings that have been blasted away. The FAA keeps strict rules about how paint or marks are removed -- they're absolutely never to be painted over, since the decay of the new mark might wear away to reveal conflicting information. Instead, airports have to sandblast or power wash the old paint away and re-do it. Which explains the light-coloured spots or words you might see on the runway.
One of the things I was always curious about were the red square signs that seem to dot every runway. It turns out those are a bit like stop signs -- the FAA says they indicate the "holding position" for a plane that's waiting to take off or get to the gate. The numbers are there to help the air traffic controller coordinate the comings and goings.
Update: Gizmodo reader TheHeadFL writes with more info about these marks: "Most of the red squares you have pictured are actually for the benefit of the pilot, not really ATC. When you get to the hold short line at a runway entrance, the red block will denote which runway you are about to enter. For example "18-36". Runway 18 runs from left to right, and Runway 36 runs from right to left."
A black sign with a number, meanwhile, usually corresponds to the number of thousands of feet left on the runway -- a guide so that pilots know roughly how much space they have left. Anything painted white is reserved for the actual runway itself -- while yellow is all about taxiing or, in some cases, no-go zones. And the yellow numbers and markings closer to the airpot? Those identify gates.
Which brings us back to the thing that sent me down this weird FAA standards rabbit hole: The lights. Though Dubai's new lighting system is comparatively new-fangled, it still adheres to the same language as most runways.
The kind of lights you'll see as a passenger depends on where you're sitting and what kind of plane you're in -- if it has a nose camera, you'll be able to check out a lot more detail. If you're just looking out the window, the kind of lights you'll see are mainly blue, which line the areas where your plane is taxiing to and from the runway, or white, which denote the touchdown area and the centerline.
According to the FAA's guidelines, green lights up the threshold, where the actual runway starts, while red always means exactly what you think it means -- do not go. You'll also notice white lights on the approach too, those distinctive short lines of light that begin long before the runway. Those are called approach lights, and they're the most powerful and important lights for a pilot coming in to land.
The FAA also mentions a "decision bar", which it turns out is the name for the single, wider line of light that directly precedes the runway after the approach bars end. This was a feature I'd always been curious about, but I couldn't find a great description in the guidelines. I turned to Flight Training, which had already done a great job of explaining these lights in aviation parlance.
It turns out that they're placed as a kind of aide during a crucial moment in landing: When the pilot transitions from flying using the cockpit instruments to flying based on what they see. FT explains:
As you look up to see the runway or approach light environment, you must, by default, take your eyes off the attitude indicator. If it's dark, rainy or snowy, (or the kids in back have their hands over your eyes), you may have difficulty identifying the lateral (bank) cues necessary to keep the aeroplane flying straight. The decision bar's horizontal spread of bright white lights acts like an external attitude indicator, providing you with visual bank references as you seek other runway cues.
Which brings us back to the original reason I got curious about runway lighting: The increasing use of LEDs on runways. While Dubai and many other airports have switched over to LEDs -- citing efficiency, durability, and even visibility -- not everyone agrees they're better. Stateside, some pilots have complained that LEDs are blinding and causing problems during landings.
I asked a commercial airline pilot named Chris Manno, who runs the blog JetHead, about the phenomenon. Manno had a completely different take on LEDs. "I've heard that, but I don't agree," he told me. "It can be a little bit of an annoyance, but it doesn't cause a problem, and in fact, I think they're an improvement over the old lights." Manno says that the lights are brighter in foggy conditions, and they make it much easier to find the runway. "We're starting to convert the aircraft landing and taxi lights because it's so much better," Manno added.
It seems like the reports of new runway lighting blinding pilots were exaggerated -- and the fact that it was a controversy at all tells us a lot about how vital all these seemingly banal systems are in keeping global air traffic in order.
When millions of flights from hundreds of countries take off and land every month, developing a standard vernacular that every pilot can read is absolutely crucial. So yeah -- it's just a bunch of lines and numbers. But it's also the vernacular that helps keep you, and everyone else, on track.