FCC Restricted GMDSS (RG) key terms

An area within radiotelephone coverage of at least one VHF coast station in which continuous DSC alerting is available, extending roughly 20 to 30 nautical miles from the coast.

An area outside Sea Area A1 but within coverage of at least one MF coast station providing continuous DSC alerting, typically extending up to about 100 nautical miles offshore.

An area outside Sea Areas A1 and A2 covered by an Inmarsat geostationary satellite service with continuous alerting, roughly between 70 degrees north and 70 degrees south latitude.

The remaining sea areas outside A1, A2 and A3, mainly the polar regions, where no VHF, MF or Inmarsat coverage exists and alerting relies on HF DSC and other long-range means.

The Global Maritime Distress and Safety System, an internationally agreed set of radio and satellite equipment, procedures and frequencies that automates distress alerting and provides maritime safety information worldwide.

A transmission sent to shore authorities and ships indicating that a vessel or person is in grave and imminent danger and requires immediate assistance, normally sent by DSC, EPIRB or satellite.

Digital Selective Calling, a digital signalling technique used on VHF, MF and HF to send preformatted alerts and calls to specific stations or all stations, followed by voice communication on a working channel.

The dedicated VHF frequency for Digital Selective Calling, reserved exclusively for DSC and never used for voice transmission because it would interfere with automated distress alerting.

The VHF radiotelephone distress, urgency and safety frequency, used for initial calls and distress traffic and monitored continuously by ships at sea when the radio is not being used for other purposes.

A VHF bridge-to-bridge navigation safety channel, used for ship-to-ship communication about manoeuvring and collision avoidance, with low transmitter power normally selected.

A VHF ship-to-ship working channel commonly used for intership safety and operational communications, particularly in search and rescue on-scene coordination.

Maritime Mobile Service Identity, a unique nine-digit number assigned to a vessel and entered into DSC and AIS equipment so that calls can be addressed to and identified from that station.

The spoken distress signal used when a vessel or person is threatened by grave and imminent danger and needs immediate assistance, spoken three times and followed by vessel identity and position.

The urgency signal used for urgent messages concerning the safety of a vessel or person but without immediate danger of loss, repeated three times and followed by the message.

The safety signal spoken three times to announce an important navigational or meteorological warning, such as a gale warning or a drifting hazard, that affects safe navigation.

The spoken control phrase meaning distress traffic silence is imposed, used by the station controlling distress communications to stop other stations from transmitting on the frequency.

The spoken phrase meaning distress traffic has ended and normal radio working may resume, announced by the station that controlled the distress communications.

Radio communication between the ship in distress, assisting ships, aircraft and rescue coordination centres at the scene of a distress incident, usually on VHF and often coordinated by an on-scene commander.

The organisation of search and rescue by a rescue coordination centre, which alerts units, designates an on-scene coordinator and directs search patterns and communications during an incident.

A shore-based unit responsible for promoting efficient organisation of search and rescue services and for coordinating the conduct of search and rescue operations within a specified search and rescue region.

An international automated system that broadcasts maritime safety information in text form on MF frequencies to ships within about 200 to 400 nautical miles of a coastal transmitter.

Maritime Safety Information, comprising navigational warnings, meteorological warnings and forecasts, search and rescue information and other urgent safety messages broadcast to ships by NAVTEX, SafetyNET or HF.

The Inmarsat enhanced group call service used to broadcast maritime safety information to ships equipped with Inmarsat terminals, covering fixed geographical areas or circular areas around a distress position.

A single-letter code identifying the type of NAVTEX message, such as navigational warnings, meteorological warnings, search and rescue information or pilot messages, which the receiver can be set to accept or reject.

Emergency Position-Indicating Radio Beacon, a float-free transmitter that on activation alerts rescue authorities via satellite and transmits a homing signal to help locate the survivors.

The satellite distress frequency used by Cospas-Sarsat EPIRBs, carrying digital identification and position data that lets rescue authorities identify the vessel and alert quickly.

The aeronautical emergency frequency transmitted by EPIRBs as a low-power homing signal that search aircraft and rescue vessels use to home in on the beacon.

Search and Rescue Radar Transponder, a battery-powered device carried in survival craft that, when interrogated by a ship or aircraft radar, shows a series of dots on the radar screen to mark the survivors' position.

A portable, battery-powered VHF transceiver carried in survival craft, operating on Channel 16 and at least one other channel, used for on-scene distress and rescue communications.

Radio communication between survival craft, ships and rescue units at the scene of a casualty, typically using portable VHF equipment on Channel 16 and a designated working channel.

A GMDSS operator qualification limited to specified equipment and sea areas, typically authorising VHF radiotelephony and DSC operation for vessels in Sea Area A1.

The authorisation issued by a national administration permitting a vessel to carry and operate radio equipment, specifying the station identity, permitted frequencies and equipment conditions.

The official record kept by the radio operator of distress, urgency and safety communications, equipment failures, battery checks and other significant radio events, retained for inspection by authorities.

The continuous listening duty maintained on the appropriate distress and safety frequencies, including DSC watch on Channel 70, while the vessel is at sea and the radio is not otherwise in use.

A periodic check confirming that a GMDSS battery can supply the required equipment for the specified period, often by measuring specific gravity or discharging under load and recording the result.

A dedicated reserve battery that powers VHF and other GMDSS equipment for a defined period if the main and emergency power supplies fail, kept fully charged and regularly tested.

Basic checks of the antenna, feeder and connectors, such as inspecting for corrosion, water ingress or loose connections, performed when transmitted range or reception quality is noticeably poor.

An unintended distress or urgency transmission, often caused by accidental DSC keying or EPIRB activation, which must be cancelled immediately by informing the rescue coordination centre.