Check GNSS position and UTC time, antenna connections, radio identities and power supplies. Do not delay a life-saving alert while correcting a missing position or filling in a log. Supply the best available position and its time, then update rescuers. For manual input, MSC.511(105) requires a warning beyond 4 h and erasure beyond 23.5 h; those thresholds do not make an inaccurate position acceptable.
The reserve radio source is independent of the main and emergency sources. SOLAS IV/13 requires 1 h where a compliant emergency supply fully powers the radio installation, otherwise 6 h. Maintenance availability uses at least one approved method in A1/A2 and a combination of at least two in A3/A4. Repair defects and assess voyage compliance with the master and responsible authority.
Start with the information that is available
A distress alert is a time-critical communication. A position that is present but old is still information; a blank position is also information. Record what the equipment actually provides, including the source and UTC time, then pass the alert without waiting for a perfect fix. A later update can improve the picture. Identity, position, time, and confidence are different fields.
Trace the position path
ITU Radio Regulations Article 32.5B addresses a GMDSS device that can transmit position but has no integral electronic position-fixing receiver. When a separate navigation receiver is installed, the equipment is to be interconnected so position can be supplied automatically. That requirement describes an arrangement; it does not certify the accuracy of the receiver, antenna, chart datum, or wiring.
Use this reading sequence:
- 1Identify the source: integral GNSS, connected receiver, or manual entry.
- 2Read the fix age and UTC time, if shown.
- 3Compare the displayed identity with the station record and voyage documents.
- 4Send the best available information; update the rescue service if the fix changes.
| Check | What it tells you | What it cannot prove |
|---|---|---|
| GNSS fix | A receiver reports a position | That the position is correct or current |
| UTC time | When the information was recorded | That every device clock agrees |
| MMSI | Which station identity is configured | That the vessel data are registered correctly |
| Antenna/power indication | Equipment has a monitored path | That transmission will reach a station |
Power is a chain, not one number
The radio installation depends on more than a battery label. Main, emergency, and reserve sources have distinct roles, and the required arrangement depends on SOLAS, sea area, ship design, and approved maintenance plan. Under SOLAS IV/13, the reserve radio source must provide at least 1 hour when a compliant emergency source fully powers the radio installation, or at least 6 hours otherwise. Those conditional figures apply to the stated SOLAS arrangement; the approved ship plan and flag administration control the applicable answer.
A useful study check is to name the source currently feeding the radio, the source intended if that fails, and the evidence that each source is available. A charge indicator is evidence about charge, not proof of endurance under the required load. Likewise, an antenna alarm identifies a monitored fault, not the complete state of the radio path.
Apply the distinction
Suppose the connected receiver shows 41° 22.4' N, 008° 43.1' W at 12:10 UTC, while the radio display reports that the fix is 18 minutes old. Preserve the coordinates and their age, send the alert using the available path, and arrange an update when a newer fix is obtained. If the radio has lost its automatic input, record that defect for the responsible operator and master.
Sources: ITU Radio Regulations 2024, Articles 32.5B and 32.9–32.10; SOLAS IV/13, MSC.496(105).
Official references · 2026-09-09
Apply what you learned
A simulated alert screen shows a connected GNSS position recorded 18 minutes ago. The vessel identity is confirmed, but the reserve battery indicator is amber.
What should you do first?
Suggested answer: Use the available position and recorded time in the simulated alert, then plan an update and flag the power issue.
Why this works: The alert is time-critical. Data age and reserve status are recorded facts, not reasons to invent a better fix or wait for a perfect battery indication. A real ship would follow its approved procedures and master's direction.
Continue with guided radio exercises.
Practise in the radio simulatorKey Takeaways
Send the best available position with its source and recorded UTC time; do not delay a life-saving alert for a perfect fix.
Automatic interconnection supplies data but does not prove position accuracy, identity correctness, or radio coverage.
Main, emergency, and reserve power are distinct and depend on the approved ship arrangement and applicable rules.
A charge, antenna, or receiver indication is evidence about one part of the chain, not a guarantee of end-to-end transmission.
Common Mistakes
Treating a stale or missing GNSS fix as a reason to postpone an alert.
Treating the one-hour or six-hour reserve figures as universal outside their stated SOLAS conditions.
Assuming a correct MMSI or a connected receiver proves that the whole radio path is correct.
Test Your Knowledge
Practise this topic and review the explanation for each answer.
More GMDSS lessons
- Module 5 — NBDP / radiotelexNBDP is narrow-band direct-printing telegraphy.
- Module 6 — Inmarsat C and EGCInmarsat-C provides data messaging, distress alerting and SafetyNET reception; it does not provide voice.
- Module 7 — NAVTEX and maritime safety informationInternational NAVTEX broadcasts on 518 kHz in English; national services may use 490 or 4209.5 kHz.
- 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.
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