Global Maritime Distress and Safety System (GMDSS) has been developed by the maritime nations in the International Maritime Organization (IMO) and is the result of their adoption of amendments made in 1988 to the 1974 International Convention on the Safety of Life at Sea (SOLAS).
Based on recent developments in maritime communications, such as satellites and digital technology, GMDSS is designed to ensure maximum availability of safety-related communication for all passenger ships as well as for cargo vessels of 300 GT and upwards engaged in international voyages.*
The goal of GMDSS is to virtually guarantee that complying vessels will be able to communicate with an onshore station at any time, from any location, in case of distress or to exchange safety-related information.
*Ships below 300 gross tonnage as well as those that are not engaged in international voyages are subject to the requirements of the administrations of their flag states.
GMDSS defines four sea areas based upon the location and capability of onshore-based communication facilities. The definition of the Sea Areas for GMDSS is outlined below.
Sea Area A1
The radiotelephone coverage of VHF coast stations in which continuous alerting by Digital Selective Calling (DSC) is available.
Sea Area A2
The radiotelephone coverage of MF coast stations in which continuous alerting by Digital Selective Calling is available.
Sea Area A3
The coverage of Inmarsat geostationary satellites.
Sea Area A4
Area outside A1, A2 and A3, mostly sea area around polar areas.