Inmarsat-C provides data messaging, distress alerting and SafetyNET reception; it does not provide voice. Other approved satellite equipment may support different services, including Iridium GMDSS with SafetyCast. Approval, installed terminal compatibility, actual coverage and service availability all matter. A consumer satellite messenger does not establish SOLAS GMDSS compliance.
Check the terminal's network status, identity, position and UTC time. Send a real distress alert using its dedicated procedure and follow up with the rescue authority through the supported distress communication service. Configure MSI reception for the voyage and check messages. If a false alert is sent, promptly notify the RCC through the system or another effective means; logging out or turning off the terminal does not cancel it.
Inmarsat-C as a data and alerting service
Inmarsat-C is a store-and-forward data service. A terminal can exchange short data messages, support distress alerting and receive maritime safety information through the Enhanced Group Call (EGC) function. It does not provide ordinary voice radiotelephony. That simple distinction prevents a common failure: selecting a text terminal when the procedure requires a voice conversation with the rescue authority.
EGC and SafetyNET
EGC is a shore-to-ship broadcast facility. ITU’s handbook description describes EGC as a data broadcast used for maritime safety information, including SafetyNET. It is therefore an MSI reception path. It is not a replacement name for DSC and it is not proof that every satellite terminal can receive every message.
| Function | Inmarsat-C/EGC lesson |
|---|---|
| Distress alert | Use the terminal’s dedicated approved alert procedure. |
| MSI reception | Configure the voyage area and read incoming broadcasts. |
| Voice follow-up | Use a supported voice or other effective RCC channel. |
The IMO GMDSS page and SOLAS IV amendments provide the regulatory context. IMO recognition of a mobile satellite service, the terminal’s type approval, the fitted equipment, network registration, actual coverage and service availability are separate checks.
A deliberate terminal workflow
- 1Confirm power, antenna or terminal status and the registered identity.
- 2Check the position and UTC time shown by the terminal.
- 3Confirm that the network is available and that the selected service covers the voyage.
- 4For practice, use a manufacturer-supported test or simulation; do not press a live distress control.
- 5For a real alert, use the dedicated procedure, then follow the supported rescue-authority communication path.
- 6If an accidental alert is sent, notify the RCC promptly by the system or another effective means and record the cancellation.
Worked insight: satellite MSI is not commercial assurance
A SafetyNET message can warn of a navigational hazard, but reception alone does not guarantee an updated passage plan or safe decision. Read the message, identify its area and validity, compare it with the voyage, and tell the bridge what action is required. EGC reception and distress alerting can share a terminal, yet they remain different functions with different follow-up steps.
Other recognized satellite systems are different approved services. Avoid latitude shortcuts: A3 is defined by recognized service coverage and the carried ship earth station, not by a universal north-south boundary.
Official references · 2026-09-09
Apply what you learned
A vessel receives a SafetyNET warning and the operator proposes replying to the broadcast as if it were a voice distress call.
What is the correct sequence?
Suggested answer: Assess the MSI, brief the bridge, and use the approved distress or voice path only if needed.
Why this works: EGC is a one-way shore-to-ship MSI broadcast. The operator must check the warning’s area and validity, assess its effect on the voyage and pass the decision onward. If a separate emergency exists, the terminal’s dedicated distress procedure and the supported RCC follow-up path must be used; replying to an MSI broadcast is not that procedure.
Continue with guided radio exercises.
Practise in the radio simulatorKey Takeaways
Inmarsat-C is a data and distress-alerting service, not ordinary voice radiotelephony.
EGC/SafetyNET is a shore-to-ship MSI broadcast function.
Recognition, approval, fitted terminal, registration, coverage and availability are separate checks.
A satellite data message does not by itself prove SOLAS compliance or RCC contact.
Accidental alerts require prompt authority notification; powering down is not cancellation.
Common Mistakes
Calling Inmarsat-C a voice service.
Treating EGC reception as DSC distress alerting.
Using a consumer messenger or a latitude rule as evidence of GMDSS status.
Test Your Knowledge
Practise this topic and review the explanation for each answer.
More GMDSS lessons
- Module 3 — VHF radiotelephony and DSCVHF channel 70 (156.525 MHz) carries DSC, never voice.
- Module 4 — MF/HF radiotelephony and DSCMF/HF DSC alerts and subsequent voice traffic use different frequencies.
- Module 8 — EPIRB / 406 MHz beaconA 406 MHz EPIRB alerts the Cospas-Sarsat system; its 121.5 MHz signal helps nearby rescue units home in.
- Module 9 — SART, AIS-SART and survival VHFA radar SART responds to suitable X-band radar and creates twelve marks extending away from its approximate position; arcs or circles can appear at close range.
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