Global Maritime Distress and Safety System

The Global Maritime Distress and Safety System is the internationally harmonised radio communication framework mandated by SOLAS Chapter IV, under which ships carry specific equipment determined by the sea areas in which they operate. GMDSS replaced the traditional Morse code watch and introduced digital selective calling on VHF, MF, and HF as the primary distress alerting method, supplemented by satellite EPIRBs, SARTs, and NavTex receivers for safety information. The system was phased in from 1992 and became fully mandatory for SOLAS vessels from 1999, with the ITU Radio Regulations providing the frequency allocations and technical standards. A SOLAS vessel's GMDSS equipment suite is determined by its declared operating area: Area A1 vessels need VHF DSC and a NAVTEX receiver; Area A2 adds MF DSC; Area A3 adds an Inmarsat terminal; Area A4 adds HF DSC. Vessels must carry two radio operators holding GMDSS certificates — the Global Maritime Distress and Safety System General Operator Certificate or the appropriate restricted certificate. Annual testing of all GMDSS equipment, battery capacity checks, and EPIRB hydrostatic release and float-free tests are required by SOLAS IV/15 and are verified by flag state surveyors and port state control officers.