GMDSS Area A1/A2/A3/A4

GMDSS sea areas A1, A2, A3, and A4 are the radiocommunication coverage zones that determine which equipment a ship must carry under the Global Maritime Distress and Safety System. SOLAS IV/2 defines them: A1 within VHF coverage of a coast station with continuous DSC alerting, A2 within MF coverage, A3 within a recognized mobile-satellite service providing continuous alerting (formerly Inmarsat-only), and A4 the remaining areas, mainly the polar regions, outside satellite coverage. The modernized Chapter IV, in force 1 January 2024, redefined A3 around recognized mobile-satellite services and broadened provider options. Carriage requirements escalate with each higher area under IV/7 to IV/11.