by Jonathan M. Stern
The ARTCC controllers generally control IFR traffic in the enroute environment. Although all the airspace over the continental United States is divided into ARTCC airspace, certain areas of airspace are delegated to the terminal facilities for IFR control. The ARTCCs, of which there are 20 in the continental United States, mostly function by radar control methods. They also have controllers who work in specialized areas such as flow control (a traffic planning and management function) and the Center Weather Service Unit, which advises the controllers on meteorological conditions that may impact traffic flows.
An ARTCC's airspace is divided into areas, which are further divided into sectors. During busy periods, there may be one controller for each sector. When the traffic is lighter, such as on the midnight shift, the sectors may be combined and worked by far fewer controllers. Table 11.2 shows the 20 ARTCCs in the continental United States and their corresponding traffic levels for FAA fiscal year 1993. The borders of an ARTCC's airspace are shown as a dotted line on enroute navigation charts.
|TABLE 11.2 The ARTCCs in the Continental United States|
|ARTCC Number||ARTCC Name||Aircraft Handled|
|18||Salt Lake City||1,354,519|
To a pilot receiving ATC services, there is no apparent difference between a TRACON and an ARTCC. One notable difference from an operational perspective is that five miles of radar separation is generally required between IFR aircraft under ARTCC control, whereas aircraft under TRACON control need only three miles separation.
As the flight progresses, Lear 12345 passes through airspace controlled by various ATC facilities. On the flight today, Lear 12345 talks with controllers at Pittsburgh Departure Control, the Cleveland ARTCC, Washington ARTCC, Atlanta ARTCC, and Atlanta Approach Control.
Each controller monitors the progress of the flight, ensuring that the requisite separation from other aircraft is maintained. When other aircraft pass at or close to the minimum distance required by the FAA's Air Traffic Control Handbook, ATC issues a traffic advisory, traffic permitting. A traffic advisory consists of the word traffic followed by the position of the other aircraft relative to that of the aircraft receiving the advisory and expressed by the positions of hours on a clock, the approximate distance in nautical miles, the direction of flight of the traffic, and the altitude, if known, of the traffic. As an example, if a DC-8 were going to pass 1,000 feet below Lear 12345's right wing, the controller might issue the following traffic advisory:
"Lear 12345, traffic three o'clock, two miles, northeast bound, one one thousand feet, a DC-8."
The appropriate response to a traffic advisory given by ATC is either "Roger" or "Traffic In Sight." "Roger" acknowledges the traffic advisory and does not indicate that the traffic is in sight.
Each time the flight is handed off to a new controller, initial contact is made after tuning the newly assigned frequency in one of the communications radios.
As Lear 12345 nears Atlanta, the destination ATIS should be monitored and pertinent information recorded on paper. Atlanta ARTCC makes a radar handoff to Atlanta Approach Control. ATC issues instructions for the flight to descend to the initial approach altitude and provides instructions or radar vectors to position the airplane so that it may fly an instrument approach to the Atlanta Airport.
If radar vectors to the final approach course are provided, ATC assigns headings to Lear 12345 so that it intercepts the final approach course at least three miles outside the final approach fix on a heading within thirty degrees of the final approach course. After the airplane is established on the final approach, Atlanta Approach Control instructs Lear 12345 to contact the Atlanta Tower. At the appropriate time, Atlanta Tower clears Lear 12345 to land.
After the landing roll is completed, the first available taxiway is used to exit the runway. At busier airports, there is a great deal of traffic and the approaches and landings occur one after the other with minimal space in between each aircraft. Atlanta Ground Control issues instructions for Lear 12345 to taxi to parking.
In the pilot/air traffic control lingo, the phonetic alphabet (listed in Table 11.3) is used in lieu of letters.
|TABLE 11.3 The Pilot's Phonetic Alphabet|