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USAF High Frequency Global Communications System

The USAF High Frequency Global Communications System is a worldwide network of 15 high-power HF stations providing command and control communications between ground agencies and US military aircraft and ships. Allied military and other aircraft are also provided support IAW agreements and international protocols as appropriate. The HFGCS is not dedicated to any service or command, but supports all DoD authorized users on a traffic precedence/priority basis.

General services provided by the HFGCS are:

  • General Phone Patch and Message Relay Services
  • Automatic Link Establishment (ALE)
  • HF Data Support
  • Command and Control Mission Following
  • Emergency Assistance
  • Broadcasts
  • HF Direction Finding Assistance
  • ATC Support
  • E-Mail connectivity to NIPRNeT and SIPRNeT



SCOPE (System Capable Of Planned Expansion) Command replaces older high power Global HF (GHFS) equipment. SCOPE Command incorporates Automatic Link Establishment (ALE) to automate communications. All HFGCS station transmit and receive equipment is remotely controlled from the Centralized Network Control Station (CNCS) at Andrews AFB, MD.

General Calling

Aircrews use a preliminary call as outlined in ACP-121 US Supp 2 using the collective callsign "MAINSAIL" or the HFGCS station call sign (example: Sigonella Global this is Dark 86 on 11175, OVER). HFGCS operators require approximately 10 seconds (for automated equipment configuration) to respond to calls for service. The HFGCS operator may request the aircraft change to a discrete frequency for improved and/or extended service.

(a) PUBLISHED FREQUENCY LISTING - HFGCS stations operate on “core�? frequencies to provide increased "Global" coverage. The published frequency listing does not reflect complete system frequency authorizations. These published frequencies will be used for initial contact, EAM broadcasts, and short-term C2 phone patch and message delivery. Other extended or special services will be moved to each station’s available "discrete" frequencies.

(b) FREQUENCY GUIDE - The frequency guides are designed to optimize air/ground communications.

 Primary HFGCS Frequencies 24 Hours:   8992 and 11175
 Back up HFGCS Frequencies Day:        13200 15016
 Back up HFGCS Frequencies Night:      4724 6739

                          DISTANCE (1)
 TIME (2)
        200-750 NM      750-1500 NM           More than 1500 NM
 0000L   4724            6712-6739-8992        6712-6739-8992-11175
 0400 L  4724            4724-6712-6739        6712-6739-8992
 0800 L  4724-6712-6739  6712-6739-8992-11175  11175-13200-15016
 1200 L  4724-6712-6739  8992-11175-13200      13200-15016
 1600 L  4724-6712-6739  8992-11175-13200      13200-15016
 2000 L  4724-6712-6739  6712-6739-8992-11175  11175-13200-15016
 1. When less than 200 NM any frequency
 2. Local time at ground station.

 STATION    4724       6712        6739        8992      11175     13200       15016
 Andrews   0500-1330Z              0300-1600Z  24 hours  24 hours  1330-0500Z  1600-0300Z
 Ascension 2300-0700Z              2200-0900Z  24 hours  24 hours  0700-2300Z  0900-2200Z
 Croughton 2300-0600Z  2100-0800Z              24 hours  24 hours  0600-2300Z  0800-2100Z
 Dieg Gar  1400-0100Z              1200-0200Z  24 hours  24 hours  0100-1400Z  0200-1200Z
 Elmendorf 0600-1500Z              0400-1700Z  24 hours  24 hours  1500-0600Z  1700-0400Z
 Guam      1300-2200Z              1100-2400Z  24 hours  24 hours  2200-1300Z  2400-1100Z
 Hawaii    0800-1700Z              0700-1800Z  24 hours  24 hours  1700-0800Z  1800-0700Z
 Lajes     2200-0800Z              2000-1200Z  24 hours  24 hours  0800-2200Z  1200-2000Z
 Offutt    0400-1330Z              0200-1700Z  24 hours  24 hours  1330-0400Z  1700-0200Z
 Puerto R  0400-1200Z              0100-1400Z  24 hours  24 hours  1200-0400Z  1400-0100Z
 Sigonella 2200-0530Z              1900-0900Z  24 hours  24 hours  0530-2200Z  0900-1900Z
 West Coas 0600-1400Z              0300-1800Z  24 hours  24 hours  1400-0600Z  1800-0300Z
 Yokota    1300-2200Z              1100-2200Z  24 hours  24 hours  2200-1300Z  2200-1100Z

 STATION   4724        6712        6739        8992      11175     13200       15016
 Andrews   2400-1200Z              2200-1400Z  24 hours  24 hours  1200-2400Z  1400-2200Z
 Ascension 2200-0800Z              2100-1000Z  24 hours  24 hours  0800-2200Z  1000-2100Z
 Croughton 1800-0600Z  1700-0900Z              24 hours  24 hours  0600-1800Z  0900-1700Z
 Diego Gar 1600-2300Z              1400-0200Z  24 hours  24 hours  2300-1600Z  0200-1400Z
 Elmendorf 0330-1630Z              0200-1800Z  24 hours  24 hours  1630-0330Z  1800-0200Z
 Guam      1300-2030Z              0800-2200Z  24 hours  24 hours  2030-1300Z  2200-0800Z
 Hawaii    0700-1600Z              0400-1800Z  24 hours  24 hours  1600-0700Z  1800-0400Z
 Lajes     1800-0730Z              1700-0900Z  24 hours  24 hours  0730-1800Z  0900-1700Z
 Offutt    0030-1330Z              2300-1400Z  24 hours  24 hours  1330-0030Z  1400-2300Z
 Puerto R  0100-1100Z              2300-1200Z  24 hours  24 hours  1100-0100Z  1200-2300Z
 Sigonella 1700-0500Z              1600-0800Z  24 hours  24 hours  0500-1700Z  0800-1600Z
 West Coas 0130-1400Z              0030-1500Z  24 hours  24 hours  1400-0130Z  1500-0030Z
 Yokota    0900-2100Z              0800-2200Z  24 hours  24 hours  2100-0900Z  2200-0800Z

Unclassified Phone Patch and Message Relay Services

(a) Phone Patch Service. Phone patching allows direct voice communications between ground agencies and aircraft by electronically connecting telephone circuits to radio transmitters and receivers. Phone patch service is reserved for official unclassified business only and shouldn’t exceed 5 minutes. Patches of more than 5 minutes or of a sensitive nature should be run on a discrete frequency. Users requesting a phone patch must include all information necessary for HFGCS operators to complete the call, such as the identity or location of the called parties and telephone number if known. Phone patches are monitored by HFGCS operators. If radio reception isn’t of sufficient quality to complete the patch, they will attempt to copy the traffic and relay it to addressees.

(b) Message Relay Service. HFGCS operators transcribe encoded or plain-text messages for aircraft or ground stations and forward them to the addresses by radio or landline. The text of the messages can be in the form of alpha-numerics, code words, plain text, acronyms, and/or numerical sequences. Aircrews may use "READ BACK" procedures when the message data is critical, or when an incomplete transmission is suspected due to poor radio reception. All messages received by Global stations will be accepted and delivered by the fastest means available according to precedence and priority.

(c) ALE - For ALE radios to operate properly, the radio must have a loaded datafill, be turned on in the “automatic�? mode and remain there the duration of the flight. If the radio is removed from the ALE mode, history tables will require time to rebuild and initial communications may be slightly degraded.

 ALE Address and Frequency Chart
 Station      ALE      Frequency
              Address  3137 4721 5708 6721 9025 11226 13215 15043 18003 23337
 Andrews      ADW       x    x    x    x    x    x     x     x     x     x
 Ascension    HAW       x    x         x    x    x     x     x     x     x
 Croughton    CRO       x    x         x    x    x     x     x     x     x
 Diego Garcia JDG       x    x    x    x    x    x     x     x     x     x
 Elmendorf    AED       x    x    x    x    x    x     x     x     x     x
 Guam         GUA       x    x    x    x    x    x     x     x     x     x
 Hawaii       HIK       x    x         x    x    x     x     x     x     x
 Lajes        PLA       x    x    x    x    x    x     x     x     x     x
 McClellan    MCC       x    x    x    x    x    x     x     x     x     x
 Offutt       OFF       x    x    x    x    x    x     x     x     x     x
 Salinas      JNR       x    x    x    x    x    x     x     x     x     x
 Sigonella    ICZ       x    x    x    x    x    x     x     x     x     
 S Atlantic   MPA       x    x    x    x    x    x     x     x     x     x
 West Coast   MCC       x    x    x    x    x    x     x     x     x     x
 Yokota       JTY       x    x         x    x    x     x     x     x     x

(d) HF Data Service. All HFGCS stations have HF data access to AUTODIN/NOVA and SACCS. HF Radio Teletype requirement has been removed by Joint Staff J6.

(e) Command and Control Mission Following. C2 agencies can use the HFGCS for mission tracking/control of their aircraft. Aircraft responsible to a C2 agency for mission tracking/control should transmit an initial contact/departure report to a Global HF System station after takeoff. The following information should be included:

  • Aircraft Call Sign
  • Departure point and time
  • Destination point and ETA
  • Relay Instructions for C2 Agencies
  • Remarks: DV codes, special instructions, etc.

d. EMERGENCY ACTION MESSAGE (EAM) BROADCASTS - Most HFGCS stations transmit high priority EAMs on published frequencies during specific broadcast periods. During EAM broadcast periods, aircraft may only transmit In-Flight Emergency traffic.

e. EMERGENCY ASSISTANCE - Distress and urgency situations should be clearly identified by the words "MAYDAY" or "PAN" as appropriate (refer ACP 121 US Supp 2, Ch 8 for definitive usage). Users should transmit present position and heading when encountering grave or serious emergency situations.

f. HF DIRECTION FINDING (DF) ASSISTANCE - HFGCS stations are capable of coordinating DF efforts between aircraft and direction finding facilities for both emergency situations and suspected spectrum interference location efforts.

(1) Emergency DF Requests. Aircraft requiring DF support should advise the HFGCS station of the nature of the emergency, a bearing (steer) or a position (fix). The HFGCS operator will arrange the support and ask the aircraft to transmit a slow count from 1 to 10 and back, followed by the aircraft call sign. The aircraft should then standby for further instructions and/or results of the service. DF facility response time will vary, depending on operating conditions, location of the aircraft, nature of request, prevailing DF facility operating commitments, type of DF facility providing the service and coordination of all concerned. The average response time is estimated at four minutes for bearings and ten minutes for positions after the slow count.

(2) DF Support for Suspected Spectrum Interference. Aircraft experiencing spectrum interference may obtain DF fix information on source of interference by calling the nearest HFGCS station and requesting Spectrum Interference DF support. The aircraft will advise the Global stations of the frequency affected, type of interference (Voice, Morse Code, Printer, Noise, etc.) and request a read-back of the information passed. A report will be filed in accordance with AFI 10-707 by the aircrew upon landing. The Andrews CNCS will report Spectrum Interference DF results via message to the AF Frequency Management Agency and the aircraft unit command post.

g. ATC SUPPORT - HFGCS is not configured to meet ATC communications routing requirements and cannot provide ATC flight following service. This service can be obtained through the appropriate Civil/ICAO ATC communications agency such as the AREA CONTROL CENTER, SECTOR RADIO, or FLIGHT INFORMATION CENTER (see section B, ICAO HF Aeronautical Station List). Global HF stations will accept emergency ATC traffic and provide phone patch or message relay support as required.

Additional Resources

  • The 2015 Digital Digest has information on the US Air Force Global HF ALE Network - see the HF Appendix for the link to this document, which is very inexpensive.

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