Operational guide · Safety & equipment

GMDSS (Global Maritime Distress and Safety System)

The system that connects a ship in distress to the whole world: what changed with the modernisation in force since 2024, and how to stay compliant with the new RMSS terminology.

SOLAS Chapter IVGMDSSRMSSradio

Operational Explanation

GMDSS is the integrated system of radio communications that guarantees, in every sea area, the ability to raise a distress alert and receive assistance. Until 2024 the system referred almost exclusively to Inmarsat as the satellite provider; the modernisation of Chapter IV has made the regulations independent of the individual provider.

1 January 2024 update: amendments to SOLAS Chapter IV enter into force replacing specific references to Inmarsat with the generic term Recognized Mobile Satellite Service (RMSS). Since 2020 the IMO has also recognized, alongside Inmarsat, Iridium as a GMDSS satellite provider: installing an RMSS-SES Iridium unit as an alternative to Inmarsat remains subject to flag State policy. Sea Area A3 is also redefined (based on RMSS coverage) and the NBDP (Narrow Band Direct Printing) function is removed for MF/HF equipment.

Regulatory Reference

SOLAS IV/15.9: the satellite EPIRB shall be tested annually for all aspects of operational efficiency, with particular attention to emission on operational frequencies, coding and registration; the test is carried out on board or at an approved shore-based station, within three months before the certificate expiry or, for cargo ships, within three months before or after the anniversary date of the Cargo Ship Safety Radio Certificate. It is the test the PSCO looks for in the radio log.
SOLAS IV/15.1-15.2: equipment shall be maintained so as to ensure the availability of the required functions. The self-test of EPIRBs and SARTs has no interval set by the Convention: it follows the manufacturer’s instructions, which typically limit it to no more than once a month, because every test irreversibly consumes the beacon’s battery. The weekly interval belongs to the DSC test call to a shore station, not to EPIRBs and SARTs.
SOLAS Chapter IV (Radiocommunications), as amended with entry into force on 1 January 2024: generic, provider-independent requirements, RMSS terminology, consolidation of VHF and SART provisions, updated Sea Areas A1-A4.

Scope of Application

Every ship subject to SOLAS Chapter IV; the specific equipment required depends on the Sea Area (A1-A4) in which the ship operates.

Procedure / How to Complete It

Perform and record DSC tests and other self-tests at the frequency and by the method prescribed by the Administration, equipment manual and shipboard radio procedures.
Make an on-air test call only where prescribed and to an available station.
Plan the separate annual EPIRB test under SOLAS IV/15.9 and retain its evidence.
Check batteries, radio log and GOC/ROC certificates.

Practical Example

Example: DSC self-test completed under the manual and radio procedure; any test call to an available station recorded; EPIRB self-test under maker instructions and the annual IV/15.9 test documented separately.

What Typically Goes Wrong

In several PSC inspections, the crew's lack of understanding of the new RMSS terminology (in place of previous specific references to Inmarsat) has caused documentary confusion, with radio certificates or equipment labels not updated to the new nomenclature, leading to requests for clarification from inspectors.

Common Mistakes Mistake Library

Mistake	Consequence	How to avoid it
Radio tests performed at a supposedly universal interval or by a universal method	Test inconsistent with applicable instructions or inappropriate on-air call	Follow Administration, manual and radio procedure; call on air only where prescribed
Annual EPIRB test not planned	Deficiency and reliability not demonstrated	Keep the IV/15.9 annual test separate from maker self-tests

What the PSCO Checks

Port State Control Officers (PSCOs) check the radio log, the validity of the GOC/ROC certificates of designated personnel, the status of the EPIRB/SART, and the consistency of the installed equipment with the declared Sea Area.

Operational Tips

Do not turn a national or equipment-specific radio interval into a universal SOLAS duty.
Keep self-tests, any on-air call and the annual EPIRB test separate.
Follow maker instructions to avoid unnecessary battery drain.

Preparation checklist

Equipment matches sea area
Tests follow Administration, manuals and radio procedure
On-air call made only where prescribed
Annual EPIRB test documented
GOC/ROC and radio log checked

FAQ

What is RMSS and why did it replace 'Inmarsat' in SOLAS texts?

RMSS (Recognized Mobile Satellite Service) is the generic term introduced by the amendments in force from 1 January 2024 to make the regulations independent of the individual satellite provider, given that since 2020 Iridium has also been recognized by the IMO as a GMDSS provider alongside Inmarsat.

Can a ship freely install Iridium instead of Inmarsat?

Installing an RMSS-SES Iridium unit as an alternative to Inmarsat is technically possible but remains subject to the ship's flag State acceptance policy.

What was removed from MF/HF equipment by the 2024 amendments?

The NBDP (Narrow Band Direct Printing) function was removed, considered obsolete technology as part of the Chapter IV modernisation.

GMDSS (Global Maritime Distress and Safety System)

Operational Explanation

Regulatory Reference

Scope of Application

Procedure / How to Complete It

Practical Example

What Typically Goes Wrong

Common Mistakes Mistake Library

What the PSCO Checks

Operational Tips

Preparation checklist

FAQ

Related Topics