LIVE* ATC air traffic control audio & radar over the skies of Atlanta and Hartsfield-Jackson International Airport

From your friends at ATCMonitor.com. © 2006 - Reproduction without permission is prohibited.

We all know what happens at about 10,000 feet. Depending on whether we're inbound or outbound, the laptop computers either come out or go away. The iPods and Walkmen are either started or stopped. The seatbelt light flashes on or blinks off.

What many, if not most, air travelers flying into and out of major airports in the United States don't recognize, however, are the much more significant changes that occur at about 14,000 feet above sea level, the altitude at which an FAA Air Traffic Control Center (ARTCC) hands control of the flight over to a Terminal Radar Control Facility (TRACON). The nation's TRACONs are arguably the most crucial link in the safe passage of aircraft to and from destinations in our most congested air corridors. TRACON controllers, as many as 50 of them in the largest installations, are responsible for airplanes during what many experts believe are the most critical phases of any flight - the initial climb after takeoff and the gradual descent prior to landing.

If you were to view an air traffic control organization chart for the United States, you'd find TRACONs right under ARTCC's, which guide airplanes while they are enroute, and just above the airport control towers in which controllers dispense landing and takeoff clearances and use radar, radio, telephones, binoculars, light gun signals, closed-circuit cameras and, occasionally, age-old hand signals to control parked and taxing aircraft and support vehicles. Typically, each TRACON will direct departing and approaching aircraft for more than one airport with the size of its operational area determined by the traffic patterns and geographic locations of the fields in its sphere of control.

As befits the world's most heavily trafficked passenger airport, Atlanta's Hartsfield-Jackson International Airport is served by a mega-TRACON that also manages dozens of other airports from its state-of-the-art facilities in suburban Peachtree City. Like controllers at all other TRACONs, most of which are not located at an airport, the professionals at Peachtree City fly "blind" - if you define "seeing" as being visually able to sight an airplane. In reality, TRACON operators "view" what is happening in the skies around them via radar, video display screens, and paper "flight strips" which provide detailed, constantly updated information on each flight in their area in a standard, almost instantly digestible form.

With Hartsfield-Jackson International alone launching or receiving an average of close to 3,000 flights a day and hosting over 83 million passengers in 2004, it isn't surprising that the Peachtree City TRACON has been receiving special attention as the FAA hustles to update the nation's air transport system's ability to cope with both tomorrow and in the future.

Among the advanced systems at the Atlanta TRACON, 20 giant high-definition, digitally controlled video screens form dedicated "display walls" depicting traffic in and out of Hartsfield, aircraft in or near the other dozens of airfields served by the facility, and landings and takeoffs from as far away as Macon, Georgia and Columbus, Ohio. The Atlanta TRACON is "open 24 hours a day, seven days a week, 365 days a year," said FAA spokesperson Jim Vallone. "Even if the Atlanta airport or one of our satellite airports are closed, we are open, ready for business. Safety is our utmost concern and priority."

In simplest terms, TRACON controllers have the same responsibilities as most other operators in the air traffic control system - ensuring safe and legal vertical and horizontal separation between aircraft, redirecting flights to avoid sudden weather emergencies such as wind shears, and maintaining final approach intervals. To accomplish these tasks, TRACON controllers use pretty much the same tools employed by enroute ATCs - Digital Surveillance Radar (DSR), radar consoles, and voice contact with pilots.

Each radar console shows data blocks representing every aircraft within the controller's sector. Typically, the data blocks show the aircraft's radio call sign, altitude, attitude (level, climbing or descending), vector, ground speed, and transponder squawk ID number (useful for entering or changing flight data in the system). Other symbols on each controller's radar screen indicate airway intersections, ground-based navigation system locations, established airways and sector limits. In addition to the individual sector displays, each TRACON controller has access to radar information on the total airspace monitored by the TRACON and can instantaneously communicate with any other controller to ensure safe passage of aircraft crossing sector boundaries.

Standard operating procedure calls for multiple controllers to handle aircraft during their final approach -- a low altitude center controller, a descent approach controller, and a final approach controller.

A center controller is responsible for creating the so-called "string of pearls" - the continuous, unbroken, miles-long line of landing lights frequently seen stretching out beyond the horizon during evening airport "rush hours." Obviously, the controller isn't at all interested in organizing an aerial lightshow, but his or her job - positioning arriving aircraft in a properly spaced, perfectly aligned flow - inevitably results in the "string" effect during busy periods. As each plane reaches a point roughly 40 miles from the airport, the center controller hands the aircraft off to the descent approach controller (sometimes called a feeder controller), who makes sure it maintains the proper rate of speed and descent until it comes into the final approach airspace. At this point, the final approach controller turns the aircraft into the approach course lined up with the runway. Once the aircraft is established on the final approach course, the aircraft is handed over to the controllers in the tower and the TRACON's work with that particular flight is finished.

Takeoffs are usually handled by one person called, logically enough, a departure controller. "Receiving" each plane from the controllers in the tower almost immediately after takeoff, the departure controller is charged with finding and routing the aircraft away

from the airport in the most expeditious way possible - a process known as giving the pilot a "preferential departure route (PDR)." At roughly 10,000-14,000 feet - there's that magic altitude again - the departure controller says goodbye to the flight and the center (ARTCC) controllers take over.

In practice, under normal weather, visibility, and traffic conditions, TRACON controllers route incoming and outgoing aircraft via clearly defined arrival and departure corridors that have been compared to freeway on and off ramps. To handle traffic arriving and departing from Hartsfield-Jackson's four east-west runways (two on each side of the terminals) TRACON controllers direct approaching aircraft to one of four virtual "gates" framing the airport on its northeast, northwest, southeast and southwest corners. Departing flights are normally given one of eight established PDRs or one of over a dozen RNAV PDR departure routes.

The combination of multiple departure and approach "tracks" and four parallel landing runways (with a 5th runway on the way by May 2006) - the longest just shy of 12,000 feet long - enables Atlanta's showcase airport to rack up some staggering numbers, as many 90 landings and 100 takeoffs an hour in good weather.

Built on the site of a defunct auto-racing track, Hartfield-Jackson Atlanta International Airport - as it is formally called - has been the world's busiest passenger airport for seven consecutive years.