USAF High Frequency Global Communications System

From The RadioReference Wiki

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. See the HFGCS document (PDF) from the UDXF (Utility DXers Forum) website for a list of current frequencies and seasonal schedules

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. See the HFGCS PDF document (linked above) for more information.

(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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