GMDSS
The different sea areas
A1 – Sea Area
An area within radiotelephone coverage of at least one VHF coast station that keeps a continuous listening watch on digital selective calling (DSC), and that are defined by a country’s authorities to be such an area.
Size of area, typically but not limited to, 0-50 nautical miles.
A2 – Sea Area
An area which is not covered by an A1 – Sea Area, and are within radiotelephone coverage of at least one MF/HF coast station that keeps a continuous listening watch on digital selective calling (DSC), and that are defined by a country’s authorities to be such an area.
Size of area, typically but not limited to, 50-250 nautical miles.
A3 – Sea Area
An area which is not covered by A1- or A2 – Sea Area, and are within coverage of the geostationary satellite system INMARSAT.
Size of area, defined by IMO, from 70-degree N to 70-degree S.
(Actual range is expected to be from 76-degree N to 76-degree S, depending on weather and atmospheric) conditions.
A4 – Sea Area
An area which is not covered by A1-, A2- or A3 – Sea Area. (Polar region)
Size of area, from 70-degree to 90-degree N and from 70-degree to 90-degree S.