1The lesson in plain words
In one sentence…
To study NBDP, separate method, service and purpose before relying on an older terminal.
What is NBDP?
It is a data method for sending characters over a maritime radio link: narrow-band direct printing, not a universal distress service.
ARQ or FEC?
ARQ uses a two-way link with acknowledgements and retries; FEC broadcasts one way, without a return acknowledgement.
When can it help?
NAVTEX uses NBDP-FEC; a retained HF terminal may receive MSI where that service is offered. Check the current service plan and manual.
What changed?
From 1 January 2024, SOLAS removed the NBDP distress-carriage requirement; that does not permit ignoring genuine distress received by an older system.
2Step by step
Safe reasoning with NBDP
- 1
Identify whether the message describes ARQ, FEC, NAVTEX or an old distress procedure.
The method and the message purpose are not the same.
- 2
Check the date and the named coast or broadcast service.
Published services can change.
- 3
Check the current plan and the retained equipment manual.
Do not assume a legacy path is available.
- 4
If distress exists, use the approved route available and follow the RCC or master.
A station in distress may use any available means to obtain assistance.
- 5
Record the message and the operational decision.
A printout alone does not show that it was assessed.
3Key data
- NBDP
- Narrow-band direct-printing telegraphy
- ARQ
- Two-way link; acknowledgements and retries
- FEC
- Broadcast without return acknowledgement
- NAVTEX
- Uses NBDP-FEC
- SOLAS, 1 January 2024
- Removed NBDP distress requirement
- HF MSI
- Where that service is provided
4Key points
- 1.
Classify the message purpose first.
- 2.
Separate carriage requirements from fitted equipment capability.
- 3.
Check the service before relying on a legacy path.
- 4.
Record the message and decision, not just the printout.
5Frequent mistakes
Wrong: "Every NBDP terminal is a current SOLAS distress route."
Right: NBDP is a method; check the available service and equipment.
Wrong: "Removing the NBDP carriage requirement removed NAVTEX."
Right: The modernization removed a carriage requirement, not NAVTEX.
Wrong: "A NAVTEX printout proves a distress alert was sent."
Right: It is MSI reception; identify the purpose and assess the message.
6Practice case & exam keys
Situation
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?
Show the answer →
The printout is MSI reception, not a distress transmission.
Why: 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.
Exam keys
If you see "ARQ", look for a two-way link, acknowledgements and retries.
If you see "FEC" or "NAVTEX", separate broadcast reception from distress alerting.
If you see "since 2024", separate carriage, published service and legacy equipment.
How to read it
The same method can appear in different messages: classify the service first, then the equipment.
An older terminal may print a real message, but the printout does not prove its purpose or a sent alert.
7Full lesson & sources
Open the full lesson (diagrams and official references)
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
8Test your knowledge
What is NBDP?
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