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Info - USAF High Frequency Global Communications System (HF-GCS) Formerly referred to as the Global High Frequency System (GHFS), this system, in use by the USAF and shared with other services, is the easiest way to get started with monitoring military communications on HF. Below is information taken from the DoD FLIP (unclassified), from pages 99 through 103. 12. USAF High Frequency Global Communications System (HF-GCS) a. GENERAL - The HF-GCS System is a worldwide network of 15 high-power HF stations providing air/ground HF command and control radio 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 HF-GCS 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 HF-GCS 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 b. MODERNIZATION - SCOPE Command replaces older high power Global HF equipment. SCOPE Command incorporates Automatic Link Establishment (ALE) to automate/ enhance communications. By Jan 03, all HF-GCS station transmit and receive equipment will be remotely controlled from the Centralized Net Control Station (CNCS) at Andrews AFB MD. c. PROCEDURES - (1) General Calling. Aircrews use a preliminary call as outlined in ACP-121 US Supp 2 using the collective callsign "MAINSAIL" or the HF-GCS station call sign (example: Sigonella Global this is Dark 86 on 11175, OVER). HF-GCS operators require approximately 10 seconds (for automated equipment configuration) to respond to calls for service. The HF-GCS operator may request the aircraft change to a discrete frequency for improved and/or extended service. (a) PUBLISHED FREQUENCY LISTING - HF-GCS 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 guide is designed to optimize air/ground communications. Primary HF-GCS Frequencies - 24 hours    8992 11175    Back up HF-GCS Frequencies - DAY    13200 15016    Back up HF-GCS Frequencies - NIGHT    4724 6739 TIME (2) DISTANCE (1) 200-7500 NM 750-1500 NM More than 1500 NM 0000L 0400 L 0800 L 1200 L 1600 L 2000 L 4724 4724 4724/6712/6739 4724/6712/6739 4724/6712/6739 4724/6712/6739 6712/6739/8992 4724 /6712/6739 6712/6739/8992/11175 8992/11175/13200 8992/11175/13200 6712/6739/8992/11175 6712/6739/8992/11175 6712/6739/8992 11175/13200/15016 103200/15016 13200/15016 1175/13200/15016 1. When less than 200 NM any frequency 2. Local time at ground station FREQUENCIES - SUMMER (Apr-Sep) STATION 4724 6712 6739 8992 11175 13200 15016 Andrews 0430-0930Z 0230-0930Z   24 hours 24 hours 0930-0230Z 0930-0230Z Ascension 2400-0700Z   1900-2400Z 24 hours 24 hours 0700-1900Z Croughton 2230-0400Z 2230-0400Z   24 hours 24 hours 0400-2230Z 0400-2230Z Diego Garcia       24 hours 24 hours     Elmendorf 1000-1300Z   0800-1400Z 24 hours 24 hours 1300-1000Z 1400-0800Z Guam 1300-2000Z   1100-2000Z 24 hours 24 hours 2000-1300Z 2000-1100Z Hawaii 1000-1600Z   0500-1000Z 24 hours 24 hours 2000-1300Z 2000-1100Z Keflavik Operational Jan 2003 Lajes     2230-0400Z 24 hours 24 hours 24 hours 0400-2230Z McClellan 0730-1300Z   0530-1300Z 24 hours 24 hours 1300-0730Z 1300-0530Z Offutt 0600-1100Z   0400-1100Z 24 hours 24 hours 1100-0600Z 1100-0400Z Puerto Rico 0300-1000Z   0100-1000Z 24 hours 24 hours 1000-0300Z 1000-0100Z Sigonella 2230-0400Z   24 hours 24 hours 24 hours 24 hours 0400-2230Z Thule Deactivates Jan 2003 24 hours 24 hours 24 hours 24 hours Yokota 1200-1930Z   1000-2130Z 24 hours 24 hours 1930-1200Z 2130-1000Z FREQUENCIES - WINTER (Oct-Mar) STATION 4724 6712 6739 8992 11175 13200 15016 Andrews 0200-1230Z 2400-1230Z   24 hours 24 hours 1230-0200Z 1230-2400Z Ascension 2400-0700Z   1900-2400Z 24 hours 24 hours 0700-1900Z Croughton 1800-0800Z 1800-0800Z   24 hours 24 hours 1800-0800Z 1800-0800Z Diego Garcia       24 hours 24 hours     Elmendorf 0230-1900Z   0230-1900Z 24 hours 24 hours 1900-0230Z 2130-0030Z Guam 1200-2030Z   1000-2030Z 24 hours 24 hours 2030-1200Z 2030-1000Z Hawaii 0800-1700Z   0400-0800Z 24 hours 24 hours   1700-0400Z Keflavik Operational Jan 2003 Lajes     1800-0800Z 24 hours 24 hours 24 hours 0800-1800Z McClellan 0500-1530Z   0300-1530Z 24 hours 24 hours 1530-0500Z 1530-0300Z Offutt 0300-1400Z   0100-1400Z 24 hours 24 hours 1400-0300Z 1400-0100Z Puerto Rico 0200-1100Z   2400-1100Z 24 hours 24 hours 1100-0200Z 1100-2400Z Sigonella 1800-0800Z   24 hours 24 hours 24 hours 24 hours 0800-1800Z Thule* 24 hours   24 hours 24 hours 24 hours     Yokota 0930-2200Z   0730-2400Z 24 hours 24 hours 2200-0930Z 2400-0730Z * Deactivates Jan 2003 (2) 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. Aircrews requesting a phone patch must include all information necessary for HF-GCS 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 HF-GCS operators and 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. HF-GCS 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 alphanumerics, 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 NATL/INTL FLIGHT DATA/PROCEDURES B-41 messages received by Global stations will be accepted and delivered by the fastest means available according to precedence and priority. (c) ALE - ALE allows automated ground agency contact by selecting the best station and best frequency without operator interaction. ALE radios make this possible by using a datafill that contains frequency, station and other pertinent information. 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 Address Frequency 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 Keflavik IKF Operational Early 2003 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 Operational Early 2003 South Atlantic MPA x x x x x x x x x x Thule   Yokota JTY x x   x x x x x x   (d) HF Data Service. All HF-GCS stations have HF data access to AUTODIN and SACCS. HF Radio Teletype requirement has been removed by Joint Staff J6. (e) Command and Control Mission Following. C2 agencies can use the HF-GCS 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 HF-GCS 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). Aircrews should transmit present position and heading when encountering grave or serious emergency situations. f. HF DIRECTION FINDING (D/F) ASSISTANCE - HF-GCS stations are capable of coordinating D/F efforts between aircraft and direction finding facilities for both emergency situations and suspected spectrum interference location efforts. (1) Emergency D/F Requests. Aircraft requiring D/F support should advise the HFGCS station of the nature of the emergency, a bearing (steer) or a position (fix). The HF-GCS 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. D/F facility response time will vary, depending on operating conditions, location of the aircraft, nature of request, prevailing DF facility operating commitments, type of D/F 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 D/F fix information on source of interference by calling the nearest HFGCS station and requesting Spectrum Interference D/F 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 D/F results via message to the AF Frequency Management Agency and the aircraft unit command post. g. ATC SUPPORT - HF-GCS 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. USAF High Frequency Global Communications System Stations Download a Large JPEG (129Kb) or 11"x17" PDF for printing (193Kb)

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