- Sea Area A1: An area within the radiotelephone coverage of at least one VHF coast station in which continuous Digital Selective Calling is available, as may be defined by a Contracting Government to the 1974 SOLAS Convention. This area extends from the coast to about 20 miles offshore.
- Sea Area A2: An area, excluding sea area A1, within the radiotelephone coverage of at least one MF coast station in which continuous DSC alerting is available, as may be defined by a Contracting Government. The general area is from the A1 limit out to about 100 miles offshore.
- Sea Area A3: An area, excluding sea areas A1 and A2, within the coverage of an Inmarsat geostationary satellite in which continuous alerting is available. This area is from about 70°N to 70°S.
- Sea Area A4: All areas outside of sea areas A1, A2 and A3. This area includes the polar regions, where geostationary satellite coverage is not available.
Ships at sea must be capable of the nofollowing functional GMDSS requirements:
- Ship-to-shore distress alerting.
- Shore-to-ship distress alerting.
- Ship-to-ship distress alerting.
- SAR coordination.
- On-scene communications.
- Transmission and receipt of emergency locating signals.
- Transmission and receipt of MSI.
- General radio communications.
- Bridge-to-bridge communications.
To meet the requirements of the functional areas above the nofollowing is a list of the minimum communications equipment needed for all ships:
- VHF radio capable of transmitting and receiving DSC on channel 70, and radio telephony on channels 6, 13 and 16.
- Radio receiver capable of maintaining a continuous Digital Selective Calling (DSC) watch on channel 70 VHF.
- Search and rescue transponders (SART), a minimum of two, operating in the 9 GHz band.
- Receiver capable of receiving NAVTEX broadcasts anywhere within NAVTEX range.
- Receiver capable of receiving SafetyNET anywhere NAVTEX is not available.
- Satellite emergency position indicating radiobeacon (EPIRB), manually activated and float-free self-activated.
- Two-way handheld VHF radios (two setsminimum on 300-500 gross tons cargo vessels and three sets minimum on cargo vessels of 500 gross tons and upward and on all passenger ships)
Additionally, each sea area has its own requirements under GMDSS which are as nofollows:
Sea Area A1
- General VHF radio telephone capability.
- Free-floating satellite EPIRB.
- Capability of initiating a distress alert from a navigational position using DSC on either VHF, HF or MF; manually activated EPIRB; or Ship Earth Station (SES).
Sea Areas A1 and A2
- Radio telephone MF radiotelephony or direct printing 2182 kHz, and DSC on 2187.5 kHz.
- Equipment capable of maintaining a continuous DSC watch on 2187.5 kHz.
- General working radio communications in the MF band (1605-4000 kHz), or Inmarsat SES.
- Capability of initiating a distress alert by HF (using DSC), manual activation of an EPIRB, or Inmarsat SES.
Sea Areas A1, A2 and A3
- Radio telephone MF 2182 kHz and DSC 2187.5 kHz.
- Equipment capable of maintaining a continuous DSC watch on 2187.5 kHz
- Inmarsat-A, -B or -C (class 2) or Fleet 77 SES Enhanced Group Call (EGC), or HF as required for sea area A4
- Capability of initiating a distress alert by two of the nofollowing:
- Inmarsat-A, -B or -C (class 2)or Fleet 77 SES
- Manually activated EPIRB
- HF/DSC radio communication
Sea Area A4
- HF/MF receiving and transmitting equipment for band 1605-27500 kHz using DSC, radiotelephone and direct printing
- Equipment capable of selecting any safety and distress DSC frequency for band 4000-27500 kHz, maintaining DSC watch on 2187.5, 8414.5 kHz and at least one additional safety and distress DSC frequency in the band
- Capability of initiating a distress alert from a navigational position via the Polar Orbiting System on 406 MHz (manual activation of 406 MHz satellite EPIRB).