1The lesson in plain words
In one sentence…
Check source, time and radio path; use the best available position and update it without delaying a life-saving alert.
Where does the position come from?
Identify integral GNSS, a connected receiver, or manual entry; the source matters too when judging the data.
What do you read with the position?
Check its age and UTC time, because an old position is still information, even when it is not current.
What do you check in the path?
Check the displayed identity, antenna connections and power; an indication does not prove the whole path.
How do you understand reserve power?
Distinguish main, emergency and reserve sources; their roles are not interchangeable and duration depends on SOLAS conditions.
2Step by step
Position, antenna and power check
- 1
Identify the source: integral GNSS, connected receiver, or manual entry.
It tells you where the data comes from.
- 2
Read the position age and UTC time, if shown.
It lets you state when it was recorded.
- 3
Compare the displayed identity with the radio record and voyage documents.
A valid MMSI does not prove a valid position.
- 4
Check antenna connections and power; record any defect.
A monitored indication does not prove transmission will arrive.
- 5
Distinguish the main, emergency and reserve sources.
Each source has different roles and conditions.
- 6
Send the best available information and update rescue services if it changes.
Do not delay a life-saving alert while correcting data.
3Key data
- Manual-entry warning
- Beyond 4 h
- Manual-entry erasure
- Beyond 23.5 h
- Reserve with full emergency
- At least 1 h
- Reserve otherwise
- At least 6 h
- Maintenance in A1/A2
- At least one approved method
- Maintenance in A3/A4
- Combination of at least two
4Key points
- 1.
Source, age, identity and update: four checks before judging a position.
- 2.
Interconnection supplies data; it does not certify accuracy, antenna, datum or wiring.
- 3.
Main, emergency and reserve sources have different roles.
- 4.
A life-saving alert does not wait for a perfect fix or a completed log.
5Frequent mistakes
Wrong: "If the GNSS position is old, I should wait before alerting."
Right: Use the best available position, state its source and age, then update it.
Wrong: "A correct MMSI proves that the position is correct too."
Right: Check the identity and the position separately.
Wrong: "A charged battery proves sufficient endurance."
Right: A charge indication does not prove endurance under the required load.
6Practice case & exam keys
Situation
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?
Show the answer →
Use the available position and recorded time in the simulated alert, then plan an update and flag the power issue.
Why: 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.
Exam keys
When «manual» appears with «4 h» and «23.5 h», remember warning first and erasure later.
When main, emergency and reserve are separated, do not mix their roles or conditions.
«A1/A2» calls for one approved method; «A3/A4» calls for a combination of at least two.
How to read it
A position is data with a source and age, not an automatic guarantee of accuracy.
Think of power as a chain: one healthy indication covers only one part.
7Full lesson & sources
Open the full lesson (diagrams and official references)
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
8Test your knowledge
What do you do if the available position is old during a life-saving alert?
Keep studying…
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