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.
Operational Explanation
GMDSS combines terrestrial and satellite communications for alerting, rescue and safety information. Availability depends on coverage, equipment, power supplies and qualified personnel; it does not automatically guarantee assistance. Provider-neutral terminology predates the 2024 modernisation.
IMO recognised Iridium on 24 May 2018 through MSC.451(99). MSC.436(99), in force from 1 January 2020, had already introduced generic references to recognised mobile satellite services. From 1 January 2024 MSC.496(105) further modernises Chapter IV, removes the NBDP requirement for distress communications and defines A3 by the RMSS supported by the ship earth station actually carried, outside A1 and A2, with continuous alerting available. MSC.451(99) · MSC.436(99) · MSC.496(105).
Regulatory Reference
SOLAS IV/15.9 separates annual EPIRB testing from shore-based maintenance. Annual testing is performed onboard or at an approved station: on passenger ships within three months before Passenger Ship Safety Certificate expiry; on cargo ships within three months before expiry or within three months before or after the Cargo Ship Safety Radio Certificate anniversary. Maintenance at an approved shore-based facility has a maximum interval of five years. Retain reports: the radio log does not replace technical test evidence. Self-tests and DSC tests follow maker instructions, the Administration and radio procedures, without assuming a universal monthly limit. MSC.496(105).
For A3/A4, SOLAS IV/15.7 requires at least two approved availability methods from equipment duplication, shore-based maintenance and at-sea electronic maintenance capability; IV/15.6 applies to A1/A2. Also check the radio reserve source of energy under IV/13.
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.
- Schedule EPIRB maintenance at an approved shore-based facility at intervals not exceeding five years (IV/15.9.2), and retain its report.
- 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
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
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 and shore-based maintenance within five years documented
- GOC/ROC and radio log checked
FAQ
Related Topics
Last substantive revision of this page: 16 September 2026 · page fingerprint c4a1ef49ca1b