A complex network of ground and air traffic controllers guide aircraft across the country.
Each day, some 25,000 commercial flights take off and land at airports around the country. Each flight depends on a complicated network of ground and air traffic controllers to make it safely from one city to another.
This summer, NPR science correspondent Joe Palca flew from Washington, D.C. to San Francisco. While on board, he recorded the conversations between the cockpit and the various control centers. Here is some of what he heard, and what it all means.
Dulles International Airport, Washington D.C.
On Thursday afternoon, June 14, a United Airlines Flight 915, a Boeing 777 aircraft, was parked at a gate in the C concourse at Washington Dulles International Airport.
There was nothing remarkable about the flight, nothing remarkable about the plane. It just happened to be the one I had a seat on.
In the interest of full disclosure, I've been addicted to listening to the conversation between pilots and air traffic controllers for some years now. I find it helps pass the time, and as long as the pilot isn't screaming "MAYDAY!" into the radio, I find the chatter soothing.
United Airlines pipes the air traffic control audio through their on-board entertainment system, and the airline was kind enough to let me record the flight I happened to be on.
Captain Bob Jordan was in command that day, joined in the flight deck by First Officer Arnie Quast. The flight was scheduled to depart at 5:25 p.m. Eastern Daylight Time.
Things didn't get off to a particularly promising start. There was a problem with the video entertainment system on the plane, and we couldn't leave until it was fixed.
A few minutes later, Captain Jordan answered the question that was occurring to a lot of us: Do we really need video entertainment? Wouldn't it be better to arrive on time and do without the movies? Captain Jordan said the people in charge of maintaining planes wanted it fixed before takeoff.
So the repairs went forward, and shortly before 6 p.m., the mechanics left the plane. After a tug pushed us back from the gate, First Officer Quast checked with Dulles Ramp for permission to taxi to the runway.
Ready for Takeoff
Ramp controllers are responsible for moving planes in and out of gates. Ground control directs the planes around the airport. So Quast switched frequencies, and contacted Dulles Ground. They directed us to Runway One Right.
Dulles Runway One Right has a parallel runway — One Left — on the west side of the airport. "One" refers to the compass heading of the runway, where zero is due north, one is 10 degrees to the east, nine is 90 degrees, or due east. Because it's a widebodied jet, flight 915 gets the extra title "heavy" when communicating with Air Traffic controllers.
There were six planes ahead of us all heading for Runway One Right, it was about 15 minutes until our turn came.
Dulles Tower is the control center that is responsible for takeoffs and landings. They gave us permission to take off.
We lifted off at about 6:21 ET. Once we were clear of the airport, we got our last instructions from the Tower before they passed us on to the next control center - Potomac Departure.
Across the Country – and Six Control Centers
Potomac Departure cleared us to climb to "one-one thousand," or 11,000 as most passengers would think of it.
A few minutes later, we were given permission to climb to 24,000, then 26,000.
Air space over the United States is divided among several different air traffic control centers. We flew through space belonging to Cleveland, Kansas City, Denver, Salt Lake City, and finally, Oakland. (Track the flight across the country, and listen to conversations between the cockpit and control centers along the way.)
The trip across the country was relatively uneventful. While in Indianapolis airspace, we were twice advised to keep an eye out for passing traffic.
Over Kansas City airspace, Captain Jordan requested permission to deviate from his flight plan 10 degrees to the right to avoid some storm clouds.
San Francisco International Airport, San Francisco, Calif.
We began our descent while still in Salt Lake City airspace. As we passed over the Sierra Mountains, Northern California approach directed us to approach the airport by flying up the San Francisco Bay, and over the San Mateo Bridge. It was a clear evening, so we were told to expect a "visual" approach.
When we had descended to 8,000 feet, Captain Jordan reported the airport was in sight.
As we continued to descend, NorCal approach informed us that at the same time we would be landing on Runway 28 Right at San Francisco International Airport, another United flight, a Boeing 767, would be landing on Runway 28 Left.
As we made our final approach, we contacted San Francisco Airport tower. They reminded us about the Boeing 767 that would be off to our left, and told us about a Boeing 757 that would be landing in front of us.
Since I was sitting on the left-hand side of the plane, I could see the Boeing 767 off to our left. It wasn't a race, but I think we landed first. And only about 35 minutes late.