The air route traffic control center (ARTCC) encompasses the en-route air traffic control system air/ground radio communications that provide safe, expeditious movement of aircraft operating on instrument flight rules (IFR) within the controlled airspace of the center. ARTCCs provide the central authority for issuing IFR clearances and nationwide monitoring of each IFR flight.
This applies primarily to the en-route phase of flight and includes weather information and other in-flight services. There are 20 ARTCCs in the conterminous United States and each center contains between 20 to 80 sectors. Each sectors’ size, shape and altitudes are determined by traffic flow, airway structure and workload. Appropriate radar and communication sites are connected to the centers by microwave links and telephone lines.
The code of federal regulations (CFRs) requires the pilot in command under IFR in controlled airspace to continuously monitor an appropriate center or control frequency. When climbing after takeoff, an IFR flight is either in contact with a radar-equipped local departure control or, in some areas, an ARTCC facility. As a flight transition to the en-route phase, pilots typically expect a handoff from departure control to a center frequency if they are not already in contact with the center.
Terminal Radar Approach Control
Terminal Radar Approach Control (TRACON) controllers work in dimly lit radar rooms located within the control tower complex or in a separate building located on (or near) the airport it serves. Using radar scopes, these controllers typically work in an area of airspace with a 50-mile radius and up to an altitude of 17,000 feet. This airspace is configured to provide service to a primary airport but may include other airports that are within 50 miles of the radar service area. Aircraft within this area are provided vectors to airports, around terrain and weather, as well as separation from other aircraft. Controllers in TRACONs determine the arrival sequence for the control tower’s designated airspace.
Air Traffic Control Tower
Controllers in this type of facility manage aircraft operations on the ground and within specified airspace around an airport. The number of controllers in the tower varies depending on the size of the airport. Small general aviation airports typically have three or four controllers, while larger international airports can have up to 15 controllers talking to aircraft, processing flight plans and coordinating air traffic flow. Tower controllers manage the ground movement of aircraft around the airport and ensure appropriate spacing between aircraft taking off and landing. In addition, it is the responsibility of the control tower to determine the landing sequence between aircraft under its control. Tower controllers issue a variety of instructions to pilots, from how to enter a pattern for landing, to how to depart the airport for their destination.
An IFR clearance is authorization by ATC for an aircraft to proceed under specified traffic conditions in controlled airspace. The purpose of this authorization is to prevent a collision between known aircraft. An IFR clearance contains specific information in the following order:
- Clearance limit – The fix, point or location to which an aircraft is cleared when issued an air traffic clearance.
- Route – A defined path to the clearance limit.
- Altitude – Usually an initially assigned altitude for the departure area with a time or location to expect higher.
- Remarks – In this latter part of an IFR clearance, you will receive a departure frequency and a discrete transponder code.