Module 9 - GMDSS & Safety Equipment
GMDSS Sea Areas, SAR, and MSI
What you will learn
Read A1, A2, A3 and A4 as nested service definitions and connect alerting to rescue coordination and maritime safety information.
The sea areas describe which shore alerting services are continuously available. They do not grade the seriousness of an incident or promise one equipment fit for every route.
A1 is within VHF coast-station radiotelephone coverage with continuous DSC alerting. A2 is within MF coast-station radiotelephone coverage with continuous DSC alerting, excluding A1. A3 is within coverage of a recognised mobile satellite service supported by the ship earth station carried, excluding A1 and A2. A4 is the remaining area outside A1, A2 and A3.
The exact route determines which services and compatible equipment matter. Moving from one sea area to another is not simply sailing beyond a fixed ring: official service coverage, the carried installation and the vessel's regulatory and operational context must be checked.
A received distress alert enters a search-and-rescue system. Rescue coordination centres evaluate information and coordinate assistance, while maritime safety information aims to prevent incidents through navigational warnings, meteorological warnings and forecasts, and other urgent safety broadcasts. The crew must both send usable data and receive relevant current information.
| Area | Continuous alerting service | Exclusion |
|---|---|---|
| A1 | VHF coast-station radiotelephone and DSC | None inside its definition |
| A2 | MF coast-station radiotelephone and DSC | Excludes A1 |
| A3 | Recognised mobile satellite service supported by the carried ship earth station | Excludes A1 and A2 |
| A4 | Remainder outside the preceding services | Outside A1, A2 and A3 |
Let the route select the service
A coastal-trained operator plans an offshore delivery and assumes the vessel's VHF/DSC fit remains the complete alerting solution.
1. Plot the service areas
Check the current official coverage relevant to each part of the intended route.
2. Match carried equipment
Confirm the installation supports the service used in the area, including position and power.
3. Match competence and rules
Check certification, carriage and operating requirements beyond the SRC revision scope.
Sense check: If the planned alert route depends on a shore service that does not cover the passage, the equipment plan and possibly the voyage must change.
Common mistake or limitation
- Assigning universal distances to A1, A2 or A3.
- Defining A3 as all satellite coverage without reference to the recognised service and carried ship earth station.
- Treating sea areas as distress-priority levels.
Recap
- A1 uses VHF DSC; A2 uses MF DSC outside A1.
- A3 uses a recognised mobile satellite service supported by the carried ship earth station outside A1 and A2.
- A4 is the remaining area; route, fit and competence must align.
Optional quick check
Section 8 of 10
What makes an area A2 rather than A1?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Continue studying GMDSS & Safety Equipment
This public lesson is part of Revision Module 9. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.