By Don Brown
For 25 years, I was an air traffic controller in what became the world's busiest facility--Atlanta Center. Now I'm just another retired guy. Yes, it was a stressful job. (It's okay, that's the first thing everybody asks.) The next thing most people want to know is, "What's a Center?"
The full name of the facility is the Atlanta Air Route Traffic Control Center. The "Air Route" portion is the important part. If you've ever stepped outside on one of those blue-sky days when airplanes leave those lingering contrails way up high, you've glimpsed my workspace. Think of an airplane en route from Miami to Chicago at 30,000 feet. Think about where it crosses the route of another airplane en route from New York to New Orleans at 30,000 feet. Controllers like me made sure they didn't cross that point in the sky at exactly the same moment.
I've never figured out a good mechanism to help people remember that I never worked in the air-traffic control tower you see at the airport. I worked in a dark room, staring at a radar scope, that was located in a small town you've never heard of, about 20 miles south of the Atlanta airport. Oh, and that's how we became the busiest facility, by the way. Atlanta airport became the world's busiest airport. We (there are about 400 air traffic controllers at the Center) worked all the airplanes in and out of the Atlanta airport for at least 100 miles in all directions. And Charlotte, North Carolina. And Birmingham, Alabama. And a bunch of other airports too.
Confused yet? I know. It's just not a world that is well known. I'll explain some parts of it further, during the week. But for now, I want to get to a really simple part of the air traffic control world. It's the part I always want you to think about first, whenever air traffic control comes up as a topic. Especially when someone tries to convince you--the taxpayer--that we need to buy a new, expensive piece of equipment. Hold this thought in your mind and I'll continue explaining (after the jump). It's the runways. It's always the runways.
If you're just the average airline passenger that wants to know why your plane is late, the key to understanding the system is the runways. If you want to be the next Administrator of the Federal Aviation Administration (FAA), you need to understand that the key to the National Airspace System (NAS) is the runways. No matter how complicated all this gets (and it is complicated) everything comes back to the runways.
Step outside and look up into the sky. How many airplanes do you see? How many airplanes do you think we could fit up there? The sky is vast and mostly empty. It is not uncommon to have 5,000 airplanes in the skies over America at any one time. The sky could easily hold a hundred times more. The problem is that they want to get back on the ground. And that takes a runway.
America is blessed with a large number of runways. We have 5,194 paved runways. That would be great if we used them all because every airplane in the sky at any one moment would have its own runway. But, as you know, that isn't the way it works. As every air traffic controller in Atlanta Center knows, they all want to land at Atlanta. At 5 p.m. on Friday.
Okay, maybe it just seemed that way. But let me use that as a mental exercise I think you will find useful. Atlanta Hartsfield-Jackson Airport has five runways. Unfortunately, you can only use three of them to land on simultaneously. (That's the rule. This is hard enough without explaining the rules right now.)
The rules say you can only have one airplane on the runway at a time. On average, it takes about 60 seconds for an airliner to land, slow down and get off the runway. The math is as simple as it is inescapable. You can land about 60 airplanes an hour per runway. With Atlanta's three (arrival) runways, that would be 180 airplanes an hour. So, for 5,000 airplanes, it would take 27.7 hours to get them all on the ground. If everything went perfectly.
Too bad there are only 24 hours in a day. And that things never go perfectly.
It's a good thing the Atlanta airport only runs about 2,724 operations (landings and takeoffs) a day. (According to my calculations anyway. 994,364 per year divided by 365 days.) With 24 hours in the day that's 113 operations per hour. Of course, Atlanta's runways look a lot like Atlanta's interstates after midnight--mostly empty--so if you cut out the hours between midnight and 6 a.m. you're left with 151 operations per hour. That sounds a lot like the way this chart on FlightAware looks.
If you're like me and hate math, this probably hasn't been that much fun. But it's important to understand the basic math of the National Airspace System. The system is run from the runways. Runway capacity is finite. You can only put so many airplanes on the ground in a given period of time. If an airline schedules more airplanes than a runway can handle in a certain period of time, nobody can change the laws of physics to make it work out. There will be delays. If a thunderstorm passes over the Atlanta airport it can wipe out all five runways for an hour. Controllers can't get that capacity back. It's gone. You can't push those 151 operations that didn't happen into the next hour. That next hour already has its own 151 operations scheduled. It doesn't matter how many "traffic lanes" you put in the sky or how close together we can put airplanes in the sky. It's how close together we can put them on the runway that counts. No matter what anybody says.
Don Brown was an air traffic controller at Atlanta Center, the busiest air traffic control facility in the world, for 25 years. During that time he was also the Facility Safety Representative for the National Air Traffic Controllers Association.