A1/A2/A3/A4 Sea Areas

The four GMDSS sea areas defined in SOLAS Chapter IV Regulation 2, set by available radio coverage and dictating the equipment a ship must carry. Area A1 sits within VHF DSC coverage of a shore station (roughly 20 to 30 nm). A2 lies within MF DSC range (roughly 100 to 150 nm) outside A1. A3 covers the geostationary satellite footprint, roughly 70 degrees N to 70 degrees S, outside A1 and A2. A4 is everything else, the polar regions beyond A3. Each contracting government declares its areas to the IMO.