1The lesson in plain words
In one sentence…
Inmarsat-C exchanges data, sends distress alerts and receives SafetyNET without voice.
What is it for?
Inmarsat-C exchanges short messages, supports distress alerting and receives MSI through EGC. It does not provide ordinary voice, so it cannot replace a voice conversation with the rescue authority.
What is EGC?
It is a shore-to-ship data broadcast for MSI, including SafetyNET. Configure the voyage area and read incoming warnings.
What do you check first?
Check the network, identity, position and UTC time; confirm compatibility, actual coverage and availability because actual coverage matters for the service.
What do you do after an accidental alert?
Notify the RCC promptly through the system or another effective means and record the cancellation; switching off does not cancel it.
2Step by step
Inmarsat-C distress alert
- 1
Confirm power, terminal or antenna status and the registered identity.
You ensure the equipment and its identity are available.
- 2
Check the position and UTC time shown by the terminal.
The alert should use the terminal's current data.
- 3
Confirm that the network is available and the service covers the voyage.
Actual coverage and availability determine whether the service works.
- 4
For practice, use a manufacturer-supported test or simulation; do not press the live control.
Practice must not send a distress alert.
- 5
For an emergency, send the alert using the terminal's dedicated procedure.
It is the approved way to alert through Inmarsat-C.
- 6
Follow the supported rescue path and, if accidental, notify the RCC and record cancellation.
Switching off the terminal does not replace notice or recorded cancellation.
3Key data
- Main function
- Data, alerting and SafetyNET
- Voice
- No ordinary voice radiotelephony
- EGC
- Shore-to-ship MSI broadcast
- Voyage MSI
- Configure area and read messages
- Checks
- Approval, compatibility, coverage, availability
- Consumer equipment
- Does not prove SOLAS compliance
4Key points
- 1.
Inmarsat-C = data, alerting and SafetyNET; no voice.
- 2.
EGC broadcasts shore-to-ship MSI; it is not DSC.
- 3.
Check network, identity, position and UTC time.
- 4.
Accidental alert: notify the RCC; switching off does not cancel it.
5Frequent mistakes
Wrong: "Inmarsat-C lets me call the RCC by voice."
Right: Use the supported distress service; Inmarsat-C does not provide ordinary voice.
Wrong: "Receiving EGC is the same as sending a DSC alert."
Right: EGC receives shore-to-ship MSI; use the dedicated procedure to alert.
Wrong: "A consumer satellite messenger proves SOLAS compliance."
Right: Approval, compatibility, coverage and availability must be checked separately.
6Practice case & exam keys
Situation
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?
Show the answer →
Assess the MSI, brief the bridge, and use the approved distress or voice path only if needed.
Why: 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.
Exam keys
If you see "voice" with Inmarsat-C, be cautious: the service does not provide ordinary voice radiotelephony.
"EGC/SafetyNET" means shore-to-ship MSI reception, not a DSC alert.
"Switch off" or "log out" after a false alert is insufficient: notify the RCC promptly.
How to read it
Think of Inmarsat-C as a data mailbox with alerting: it handles messages and SafetyNET, but voice conversation needs another supported path.
When you read "coverage", separate recognized service, fitted terminal, available network and actual coverage; none replaces those checks.
7Full lesson & sources
Open the full lesson (diagrams and official references)
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
8Test your knowledge
What should you do to send a real Inmarsat-C alert?
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