The GMDSS - Global Maritime Distress and Safety System
is a worldwide system of distress, urgency and safety introduced by the IMO for maritime navigation, which uses satellites and digital selective calling technology on MF, HF and VHF. Emergency communications in the GMDSS system are organized in the four sea areas named A1, A2, A3 and A4 in which all vessels in relation to their location must have the radio equipment needed to make sure that the distress call can be sent, received and repeated at any time.
The sea areas A1/A2/A3/A4 are conform to SOLAS regulations. The necessary GMDSS equipment on ships depends from SOLAS and Flag-states and Class-regulations. Additional there are e.g. regulations for Safe-Return-to-Port (SRtP) and Polar-Code. The international GMDSS regulations apply to "compulsory" ships, including:
- Cargo ships of 300+ GT and over when traveling on international voyages or in the open sea
- All passenger ships carrying more than 12 passengers when traveling on international voyages or in the open sea