Air Route Traffic Control Center


  • Air Route Traffic Control Centers (ARTCC), also referred to as "centers," are established primarily to provide air traffic service to aircraft operating on an Instrument Flight Rule (IFR) Flight Plan within controlled airspace
  • This service is provided principally during the en route phase


  • Issues route assignment (ARTCC coordinates based on your clearance)
  • May operate from Remote Center Air/Ground sites (RCAG) to cover distance
  • Verifies/assigns altitude
  • Provides traffic separation
  • Furnishes vectors
    • If ARTCC asks your intentions at the destination airport then they are trying to plan your descent to give you to approach who will vector you for your approaches
  • Issues Notice to Airmen (NOTAMs)
  • Provides current weather information as required


  • Control begins at 1,200' Above Ground Level (AGL) on airways
  • Most IFR traffic is under direct ARTCC radio control, or works through an FSS which relays information to or from the ARTCC
  • All traffic in Class Alpha airspace which starts at 18,000' MSL, is under Center's direct control
  • Frequency Change:
    • ATC: "[call sign], contact [facility], [frequency]"
  • RADAR:
    • PILOT: "[location] center, [call sign], (level / climbing to / leaving / descending to) [altitude]"
  • Non-RADAR:
    • PILOT: "[location] center, [call sign], [position], [altitude], estimating [location], at [time]"

Direct Communications, Controllers and Pilots:

  • ARTCCs are capable of direct communications with IFR air traffic on certain frequencies
    • Maximum communications coverage is possible through the use of RCAG sites comprised of both VHF and UHF transmitters and receivers
    • These sites are located throughout the U.S. Although they may be several hundred miles away from the ARTCC, they are remoted to the various ARTCCs by land lines or microwave links
    • Since IFR operations are expedited through the use of direct communications, pilots are requested to use these frequencies strictly for communications pertinent to the control of IFR aircraft
    • Flight plan filing, en route weather, weather forecasts, and similar data should be requested through FSSs, company radio, or appropriate military facilities capable of performing these services
  • An ARTCC is divided into sectors
    • Each sector is handled by one or a team of controllers and has its own sector discrete frequency
    • As a flight progresses from one sector to another, the pilot is requested to change to the appropriate sector discrete frequency
  • Controller Pilot Data Link Communications (CPDLC) is a system that supplements air/ground voice communications
    • As a result, it expands two-way air traffic control air/ground communications capabilities
    • Consequently, the air traffic system's operational capacity is increased and any associated air traffic delays become minimized
    • A related safety benefit is that pilot/controller read-back and hear-back errors will be significantly reduced
    • The CPDLC's principal operating criteria are:
      • Voice remains the primary and controlling air/ground communications means
      • Participating aircraft will need to have the appropriate CPDLC avionics equipment in order to receive uplink or transmit downlink messages
      • CPDLC Build 1 offers four ATC data link services. These are altimeter setting (AS), transfer of communications (TC), initial contact (IC), and menu text messages (MT)
        • Altimeter settings are usually transmitted automatically when a CPDLC session and eligibility has been established with an aircraft. A controller may also manually send an altimeter setting message

When conducting instrument approach procedures, pilots are responsible to obtain and use the appropriate altimeter setting in accordance with 14 CFR Section 97.20. CPDLC issued altimeter settings are excluded for this purpose

      • Initial contact is a safety validation transaction that compares a pilot's initiated altitude downlink message with an aircraft's ATC host computer stored altitude. If an altitude mismatch is detected, the controller will verbally provide corrective action
      • Transfer of communications automatically establishes data link contact with a succeeding sector
      • Menu text transmissions are scripted non-trajectory altering uplink messages

Initial use of CPDLC will be at the Miami ARTCC. Air carriers will be the first users. Subsequently, CPDLC will be made available to all NAS users. Later versions will include trajectory altering services and expanded clearance and advisory message capabilities

ATC Frequency Change Procedures:

  • As flights proceed along a route pilots will move from one sector or ARTCC to another
  • The following phraseology will be used by controllers to effect a frequency change:
    • Pilots are expected to maintain a listening watch on the transferring controller's frequency until the time, fix, or altitude specified. ATC will omit frequency change restrictions whenever pilot compliance is expected upon receipt
      • Example: "[Aircraft identification] contact [Facility name or location name and terminal function] [Frequency] at [Time, fix, or altitude]"
  • The following phraseology should be utilized by pilots for establishing contact with the designated facility:
    • When operating in a radar environment: On initial contact, the pilot should inform the controller of the aircraft's assigned altitude preceded by the words "level," or "climbing to," or "descending to," as appropriate; and the aircraft's present vacating altitude, if applicable
      • Exact altitude or flight level reports on initial contact provide ATC with information required prior to using Mode C altitude information for separation purposes
      • Exact altitude or flight level means to the nearest 100 foot increment
        • Pilot: "[Facility] center, [Aircraft identification], level [Altitude or Flight Level]"
        • ATC: "[Facility] center, [Aircraft Identification], leaving [Exact Altitude or Flight Level], climbing to or descending to [Altitude of Flight Level]"
    • When operating in a non-radar environment:
      • On initial contact, the pilot should inform the controller of the aircraft's present position, altitude and time estimate for the next reporting point
        • Example: [Facility] center, [Aircraft Identification], [Position], [Altitude], estimating [Reporting Point] at [Zulu Time]"
      • After initial contact, when a position report will be made, the pilot should give the controller a complete position report
        • Example: [Facility] center, [Aircraft Identification], [Position], [Zulu Time], [Altitude], [Type of Flight Plan], [ETA and Name of Next Reporting Point], [The Name of the Next Succeeding Reporting Point], and [Remarks]"
  • At times controllers will ask pilots to verify that they are at a particular altitude
    • The phraseology used will be: Verify at Altitude"
    • In climbing or descending situations, controllers may ask pilots to "Verify assigned altitude as [Altitude]"
    • Pilots should confirm that they are at the altitude stated by the controller or that the assigned altitude is correct as stated
      • If this is not the case, they should inform the controller of the actual altitude being maintained or the different assigned altitude
      • Pilots should not take action to change their actual altitude or different assigned altitude to the altitude stated in the controllers verification request unless the controller specifically authorizes a change

ARTCC Radio Frequency Outage:

  • ARTCCs normally have at least one back-up radio receiver and transmitter system for each frequency, which can usually be placed into service quickly with little or no disruption of ATC service
  • Occasionally, technical problems may cause a delay but switchover seldom takes more than 60 seconds
  • When it appears that the outage will not be quickly remedied, the ARTCC will usually request a nearby aircraft, if there is one, to switch to the affected frequency to broadcast communications instructions
  • It is important, therefore, that the pilot wait at least 1 minute before deciding that the ARTCC has actually experienced a radio frequency failure
  • When such an outage does occur, the pilot should, if workload and equipment capability permit, maintain a listening watch on the affected frequency while attempting to comply with the following recommended communications procedures:
    • If two-way communications cannot be established with the ARTCC after changing frequencies, a pilot should attempt to recontact the transferring controller for the assignment of an alternative frequency or other instructions
    • When an ARTCC radio frequency failure occurs after two-way communications have been established, the pilot should attempt to reestablish contact with the center on any other known ARTCC frequency, preferably that of the next responsible sector when practicable, and ask for instructions
      • However, when the next normal frequency change along the route is known to involve another ATC facility, the pilot should contact that facility, if feasible, for instructions
      • If communications cannot be reestablished by either method, the pilot is expected to request communications instructions from the FSS appropriate to the route of flight
        • The exchange of information between an aircraft and an ARTCC through an FSS is quicker than relay via company radio because the FSS has direct interphone lines to the responsible ARTCC sector
        • Accordingly, when circumstances dictate a choice between the two, during an ARTCC frequency outage, relay via FSS radio is recommended

In-Flight Weather Broadcasts:

  • Weather Advisory Broadcasts:
    • ARTCCs broadcast Severe Weather Forecast Alert (AWW), Convective SIGMETs, SIGMETs, and/or Center Weather Advisories (CWAs) on all frequencies, except emergency, when any part of the area described is within 150 miles of the airspace under their jurisdiction
    • These broadcasts contain SIGMET or CWA (identification) and a brief description of the weather activity and general area affected
  • Examples:
    • ATC: "Attention all aircraft, SIGMET Delta Three, from Myton to Tuba City to Milford, severe turbulence and severe clear icing below one zero thousand feet. Expected to continue beyond zero three zero zero zulu"
    • ATC: "Attention all aircraft, convective SIGMET Two Seven Eastern. From the vicinity of Elmira to Phillipsburg. Scattered embedded thunderstorms moving east at one zero knots. A few intense level five cells, maximum tops four five zero"
    • ATC: "Attention all aircraft, Kansas City Center weather advisory one zero three. Numerous reports of moderate to severe icing from eight to niner thousand feet in a three zero mile radius of St. Louis. Light or negative icing reported from four thousand to one two thousand feet remainder of Kansas City Center area"
  • Terminal control facilities have the option to limit the AWW, convective SIGMET, SIGMET, or CWA broadcast as follows: local control and approach control positions may opt to broadcast SIGMET or CWA alerts only when any part of the area described is within 50 miles of the airspace under their jurisdiction
  • In areas where HIWAS is available, ARTCC, Terminal ATC, and FSS facilities no longer broadcast Inflight Weather Advisories as described above in paragraph a. See paragraphs b1 and b2 below
  • Hazardous Inflight Weather Advisory Service (HIWAS)
    • HIWAS is an automated, continuous broadcast of inflight weather advisories, provided by FSS over select VOR outlets, which include the following weather products: AWW, SIGMET, Convective SIGMET, CWA, AIRMET (text [WA] or graphical [G-AIRMET] products), and urgent PIREP. HIWAS is available throughout the conterminous United States as an additional source of hazardous weather information. HIWAS does not replace preflight or inflight weather briefings from FSS or real-time weather updates from Enroute Flight Advisory Service (EFAS), radio call "Flight Watch." Pilots should call FSS or Flight Watch if there are any questions about weather that is different than forecasted or if the HIWAS broadcast appears to be in error
    • Where HIWAS is available, ARTCC and terminal ATC facilities will broadcast, upon receipt, a HIWAS alert once on all frequencies, except emergency frequencies. Included in the broadcast will be an alert announcement, frequency instruction, number, and type of advisory updated; for example, AWW, SIGMET, Convective SIGMET, or CWA
    • Example: Attention all aircraft. Hazardous weather information (SIGMET, Convective SIGMET, AIRMET (text [WA] or graphical [G-AIRMET] product), Urgent Pilot Weather Report [UUA], or Center Weather Advisory [CWA], Number or Numbers) for (geographical area) available on HIWAS, Flight Watch, or Flight Service frequencies
    • Upon notification of an update to HIWAS, FSS will broadcast a HIWAS update announcement once on all frequencies except emergency frequencies. Included in the broadcast will be the type of advisory updated; for example, AWW, SIGMET, Convective SIGMET, CWA, etc
    • Example: Attention all aircraft. Hazardous weather information for (geographical area) available from Flight Watch or Flight Service
    • HIWAS availability is notated with VOR listings in the Airport/Facility Directory (A/FD), and is shown by symbols on IFR Enroute Low Altitude Charts and VFR Sectional Charts. The symbol depiction is identified in the chart legend
  • See more here

Air Route Traffic Control Centers
Figure 1: Air Route Traffic Control Centers


  • There are 22 Air Route Control Centers across the United States
    • ZMA: Miami Center
    • ZJX: Jacksonville Center
    • ZDC: Washington D.C. Center
    • ZNY: New York Center
    • ZBW: Boston Center
    • ZOB: Cleveland Center
    • ZID: Indianapolis Center
    • ZTL: Atlanta Center
    • ZHU: Houston Center
    • ZME: Memphis Center
    • ZKC: Kansas City Center
    • ZAU: Chicago Center
    • ZMP: Minneapolis Center
    • ZFW: Fort Worth Center
    • ZAB: Albuquerque Center
    • ZDV: Denver Center
    • ZLC: Salt Lake City Center
    • ZLA: Los Angeles Center
    • ZOA: Oakland Center
    • ZSE: Seattle Center
    • ZAN: Anchorage Center
    • Air Route Traffic Control Center Borders
      Figure 2: Air Route Traffic Control Center Borders
    • ZHN: Honolulu Center