NBDP is narrow-band direct-printing telegraphy. ARQ uses a two-way link with acknowledgements and retransmissions. FEC provides broadcast reception without a return acknowledgement. NAVTEX uses NBDP-FEC; HF NBDP broadcasts may also carry MSI where that service is provided.
The SOLAS modernization effective 1 January 2024 removed NBDP distress-communication carriage requirements. It did not abolish NAVTEX or permit operators to ignore a genuine distress message received by an older system. A station in distress may use any available means to obtain assistance. Verify current broadcast services and use the equipment instructions for retained legacy installations.
What NBDP actually does
Narrow-band direct-printing (NBDP) is a data method for sending characters over a maritime radio link. It is useful to distinguish the method from the purpose of a message. ARQ is a two-way mode: the receiving station acknowledges blocks and missing blocks can be retransmitted. FEC is a one-way broadcast mode: the receiver reconstructs the message without returning an acknowledgement. The same vocabulary appears in older radiotelex material, but it does not tell you whether a service is still provided today.
Current status after the GMDSS modernization
The 2024 SOLAS amendments removed the NBDP distress-communication carriage requirement. The MCA bulletin on HF services records the cessation of specified 2W-NBDP HF distress and safety services at the end of 2023. This is a change in required and published service arrangements, not a command to erase every old terminal.
| Mode | Return path | Typical teaching meaning |
|---|---|---|
| ARQ | Yes | A connected exchange with acknowledgements and retries. |
| FEC | No | A broadcast received without a return acknowledgement. |
NAVTEX still uses NBDP-FEC in the receiver chain. A retained HF NBDP terminal may also receive an MSI broadcast where that service is actually offered. Check the current service plan and the equipment manual before relying on a legacy path.
A safe reasoning workflow
- 1Identify whether the exercise describes ARQ, FEC, NAVTEX or an old distress procedure.
- 2Check the date and the named coast or broadcast service.
- 3Separate a carriage rule from the capabilities of equipment already fitted.
- 4If distress exists, use the available approved route and follow the RCC or master’s instructions.
- 5Record the message and the operational decision; a printout alone is not an assessment.
Worked insight: NAVTEX is not a distress relay
A receiver marked “NBDP-FEC” is not thereby a distress transmitter. NAVTEX is a scheduled MSI broadcast, while a distress alert is an alerting function with its own approved equipment and procedures. The encoding family may overlap, but the operational role does not. Use the ITU-R M.540 background to understand direct-printing MSI, then return to the applicable SOLAS and service documents for current obligations.
Historical NBDP literacy remains useful, but a particular HF broadcast, national coast station or legacy terminal must never be assumed available on a voyage.
Official references · 2026-09-09
Apply what you learned
A trainee receives a clear NAVTEX printout on an older terminal and says the vessel has therefore sent a distress alert.
What must the trainee correct?
Suggested answer: The printout is MSI reception, not a distress transmission.
Why this works: NBDP-FEC describes how characters are broadcast. It does not identify the message purpose or prove an alert was sent. The trainee should identify the NAVTEX service, assess the warning, pass relevant information to the bridge, and use the vessel’s approved distress equipment and procedure if an emergency exists.
Continue with guided radio exercises.
Practise in the radio simulatorKey Takeaways
NBDP describes a direct-printing data method, not a universal distress service.
ARQ acknowledges and retries; FEC broadcasts without a return acknowledgement.
2024 SOLAS removed the NBDP distress-carriage requirement while legacy services may still exist.
NAVTEX remains an MSI broadcast and must not be confused with distress alerting.
Common Mistakes
Treating every NBDP terminal as a current SOLAS distress route.
Assuming that removal of a carriage requirement stopped every NBDP broadcast.
Confusing the FEC transmission method with the safety purpose of NAVTEX.
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 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.
- 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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