NAVTEX and the 406 MHz EPIRB

1The lesson in plain words

In one sentence

A 406 MHz EPIRB alerts Cospas-Sarsat; 121.5 MHz helps nearby units locate it.

What does it do?

An EPIRB starts the rescue alert; it does not replace the survival plan or follow-up communication.

When do you activate it?

When distress assistance is needed; do not wait for sinking. The float-free release is intended to release it if the vessel sinks.

What do you check?

The coded identity and registration must match the real beacon; battery, release and national approval are part of readiness.

How do you test it?

Use the manufacturer’s self-test only. A self-test is not a distress transmission and live activation is not a test.

2Step by step

EPIRB activation and checks

1
Decide whether the situation needs distress assistance now.
Activate when help is needed; do not wait for sinking.
2
Take the assigned beacon or allow approved float-free release.
The float-free release is intended to release it as the vessel sinks.
3
Activate it using the marked procedure and clear its obstructions.
The release must remain clear so the beacon can separate.
4
Keep it upright and visible as far as conditions permit.
This is the stated way to keep it operating after activation.
5
Use the manufacturer’s self-test only to check it.
A self-test is not a live distress transmission.
6
After accidental activation, stop transmission through the supported procedure.
Cancellation must follow the procedure supported by the equipment.
7
Notify the RCC with identity, position and time, and record the cancellation.
The RCC needs to identify the accidental alert and its time.

3Key data

Primary alert: 406 MHz · Cospas-Sarsat
Local homing: 121.5 MHz
Additional locating: GNSS and AIS, where fitted
First generation: 15 hexadecimal characters
Second generation: 23 hexadecimal characters
Release: Before 4 m depth

4Key points

1
Identity and registration must match the real vessel.
2
Keep the release clear; do not tie the lanyard to the ship.
3
Manufacturer self-test, never live activation as a test.
4
Accidental activation: stop, notify the RCC and record the cancellation.

5Frequent mistakes

Wrong: "The lanyard should stay tied to the vessel."
Right: Keep the release clear and do not tie the lanyard so the beacon can separate.
Wrong: "I will wait for the vessel to sink before activating the EPIRB."
Right: Activate when distress help is needed; do not wait for sinking.
Wrong: "Live activation is a suitable test."
Right: Use the manufacturer’s self-test only; live activation is for distress.

6Exam keys & interpretation

Exam keys

When you see “406 MHz”, link it to the Cospas-Sarsat alert, not local homing.
When “121.5 MHz” appears, look for local homing with suitable rescue equipment.
If identity is asked, choose the real beacon: first generation 15; second generation 23 hexadecimal characters.

How to read it

Think of the EPIRB as the alert’s beginning: rescue still needs communication, survival and instructions.
The fitted equipment matters: GNSS, AIS, registration and approval depend on the real beacon and installation.

7Go deeper: GOC exam level

The detail behind each step for the General Operator's Certificate: the rules, the radio technique and worked cases.

The Cospas-Sarsat chain

An EPIRB (Emergency Position-Indicating Radio Beacon) exists to put a distress alert into the Cospas-Sarsat system. SOLAS ships carry a 406 MHz float-free EPIRB that activates automatically if the ship sinks, provided it is correctly installed and armed.

1The beacon transmits a coded digital message in the 406.0–406.1 MHz band.
2The satellite constellation (LEOSAR in low orbit, GEOSAR in geostationary orbit and MEOSAR on navigation satellites in medium orbit) relays or detects it.
3Local User Terminals (LUTs) on the ground process the satellite data.
4Mission Control Centres (MCCs) distribute the alert to the responsible RCC/MRCC.
5The RCC correlates the beacon identity, its registration, the position and any other sources before and during the response.

Position and homing

Signal	What it gives rescuers
406 MHz digital message	The alert, the beacon identity and, if fitted, an encoded GNSS position
Position from the satellite system	Doppler or MEOSAR location even without GNSS, with some delay and uncertainty
121.5 MHz homing	A signal that aircraft and rescue units can direction-find in the final approach
AIS locating (EPIRB-AIS)	A position on AIS1/AIS2 visible to nearby ships and aircraft on their AIS displays

Float-free and the hydrostatic release unit

The HRU frees the beacon when the ship sinks to a few metres. The installation must let the beacon float free without getting caught on structure, then activate as designed.

Registration, tests and maintenance

Register the beacon with the Administration and keep vessel and emergency-contact details current. The RCC uses this data to verify the alert.
Use only the manufacturer's self-test. Never generate a real alert to "see if it works".
Check the battery and HRU expiry dates.
SOLAS requires an annual test and shore-based maintenance at intervals not exceeding five years, under IMO guidance and the Administration's rules.
After an accidental activation, switch the beacon off and tell the nearest RCC or coast station immediately. Do not just put it back in the bracket.

Check	Typical interval
Visual check: bracket, HRU, antenna, no obstruction	Each watch round / weekly
Self-test per manufacturer	Monthly
Annual test (frequency, coding, registration, battery)	Every 12 months
Shore-based maintenance	Not more than 5 years
HRU replacement	At the expiry date, typically 2 years for disposable units

Beacon identity and the second generation

Every 406 MHz beacon has a unique identity, shown on its label as a 15-hex ID (fifteen hexadecimal characters). Second-generation beacons carry a longer 23-hex ID. The ID is coded from the country code and the MMSI or another serial, and it is the key the RCC uses to find the registration.

Feature	First generation	Second generation
Identity on label	15-hex ID	23-hex ID
Best satellite system	LEOSAR/GEOSAR, also detected by MEOSAR	Designed for MEOSAR
First alert and position	Can take longer without GNSS	Faster first alert and more accurate independent location
Return link	Only on some newer RLS models	Optional Return Link Service via Galileo: a light on the beacon confirms the alert was received

Man-overboard devices are not EPIRBs. An AIS-MOB transmits on AIS1/AIS2 with an identity 972XXYYYY; some also send a DSC alert on Channel 70 to the own ship (closed loop) or to all stations (open loop). They help the ship recover its own crew; they do not replace the 406 MHz EPIRB.

References: MSC.471(101) — 406 MHz float-free EPIRB performance standards · SOLAS IV as amended by MSC.496(105)

GOC exam check

On which band does a Cospas-Sarsat EPIRB transmit its distress alert?
1. 121.5 MHz
2. 243 MHz
3. 406.0–406.1 MHz
4. 1.6 GHz
Show the answer
C. 406.0–406.1 MHz
Why: The digital alert goes out on 406.0–406.1 MHz. 121.5 MHz is now used only for final homing, and 1.6 GHz was the old Inmarsat-E service.
In the Cospas-Sarsat chain, who passes the processed alert to the responsible RCC?
1. The Local User Terminal (LUT)
2. The Mission Control Centre (MCC)
3. The land earth station (LES)
4. The nearest coast station
Show the answer
B. The Mission Control Centre (MCC)
Why: LUTs process the satellite data; MCCs distribute the alert to the RCC. The LES belongs to the ship-earth-station chain, not Cospas-Sarsat.
What does the 121.5 MHz signal from a modern EPIRB give rescuers?
1. A homing signal for the final approach
2. The satellite alert and the beacon identity
3. An encoded GNSS position for the RCC
4. A voice channel to talk to survivors
Show the answer
A. A homing signal for the final approach
Why: 121.5 MHz is for direction finding in the final approach. Satellite processing of 121.5 MHz ended on 1 February 2009; the alert and position travel on 406 MHz.
What is the maximum interval for shore-based maintenance of a SOLAS EPIRB?
1. 12 months
2. 2 years
3. 4 years
4. 5 years
Show the answer
D. 5 years
Why: Shore-based maintenance is at intervals not exceeding five years. 12 months is the annual test and 2 years the typical life of a disposable HRU.
Your EPIRB is activated by accident while being moved. What should you do?
1. Put it back in the bracket so it resets itself
2. Leave it on until the RCC calls the owner
3. Switch it off and tell the nearest RCC
4. Switch it off and note it at the next annual test
Show the answer
C. Switch it off and tell the nearest RCC
Why: Switch it off and tell the nearest RCC or coast station immediately. Just putting it back or noting it later leaves a false alert running in the SAR system.
How long is the beacon identity on the label of a second-generation 406 MHz EPIRB?
1. 15 hexadecimal characters
2. 23 hexadecimal characters
3. 9 digits, like an MMSI
4. 12 hexadecimal characters
Show the answer
B. 23 hexadecimal characters
Why: Second-generation beacons carry a 23-hex ID; first-generation beacons a 15-hex ID. The ID may be coded from the MMSI but is not the MMSI itself.
During a survey you find the float-free EPIRB secured with an extra lashing for heavy weather. What is your assessment?
1. Acceptable if the HRU is still in date
2. Acceptable once the monthly self-test passes
3. Acceptable if it is removed before abandoning
4. Unacceptable: it can stop the beacon floating free
Show the answer
D. Unacceptable: it can stop the beacon floating free
Why: An improvised lashing can defeat float-free when the ship sinks. A valid HRU or passed self-test does not help if the beacon cannot surface.
The owner suggests giving every crew member an AIS-MOB device and dropping the 406 MHz EPIRB. Why is that wrong?
1. MOB devices do not alert Cospas-Sarsat
2. MOB devices need a separate ship station licence
3. MOB devices transmit only on 121.5 MHz
4. MOB devices work only with a radar SART
Show the answer
A. MOB devices do not alert Cospas-Sarsat
Why: An AIS-MOB transmits on AIS1/AIS2 to help the ship recover its own crew; it does not replace the 406 MHz EPIRB. It does not use 121.5 MHz.
At 0300 UTC, 200 NM offshore, the cargo shifts and the master orders abandon ship. The float-free 406 MHz EPIRB, which has no AIS, is in its bracket on the monkey island and there are a few minutes to spare. What do you do with it?
1. Release it by hand, activate it and tie it to the raft
2. Leave it in the bracket; the HRU will free it later
3. Activate it in its bracket and leave it on the ship
4. Release it and throw it into the sea well clear of the rafts
Show the answer
A. Release it by hand, activate it and tie it to the raft
Why: If time allows, take the beacon by hand even if it is float-free, activate it and secure it to the raft so it marks the survivors. Relying on the HRU is the tempting choice, but the beacon would then drift away from the crew.
Same scenario: hours later a helicopter is approaching your liferaft in poor visibility. Which signal from your beacon can it home on in the final approach?
1. 406 MHz, the digital alert frequency
2. AIS1, on 161.975 MHz
3. Channel 16, on 156.8 MHz
4. 121.5 MHz, the homing signal
Show the answer
D. 121.5 MHz, the homing signal
Why: The 121.5 MHz signal is for direction-finding in the final approach. The 406 MHz message carries the alert and position to Cospas-Sarsat, and this beacon has no AIS, so AIS1 is not an option.

8Full lesson & sources

Open the full lesson (diagrams and official references)

A 406 MHz EPIRB alerts the Cospas-Sarsat system; its 121.5 MHz signal helps nearby rescue units home in. The applicable modern IMO standard adds GNSS and AIS locating capability for EPIRBs installed from 1 July 2022. First-generation beacon identifiers have 15 hexadecimal characters; second-generation identifiers have 23. Registration and national equipment approval must match the actual beacon.

Keep the float-free release unobstructed. The release mechanism must operate before 4 m depth; do not tie the lanyard to the ship. Use the beacon when distress assistance is needed, without waiting for sinking. Follow the manufacturer self-test procedure; coded test emissions are possible. After accidental activation, stop transmission, contact the RCC with identity, position and time, and record the cancellation.

What an EPIRB contributes

An EPIRB is a beacon that alerts rescuers when nobody on board can use a radio. Its 406 MHz transmission alerts the Cospas-Sarsat system. Every 50 seconds or so it sends a short digital burst containing its unique identity and, if it has a GNSS receiver, its position. Satellites pick up the burst, ground stations process it, and the alert reaches the responsible RCC. A separate low-power signal on 121.5 MHz lets aircraft and lifeboats home in on it during the final approach, and newer beacons also transmit an AIS position.

The RCC sees a beacon identity, not a ship name. It looks the identity up in the registration database to find out whose beacon it is, then often calls the emergency contact. That is why an unregistered or wrongly registered beacon slows down a rescue.

Signal	Who uses it	Typical timing
406 MHz with encoded GNSS position	RCC, via Cospas-Sarsat	Often within minutes on MEOSAR
406 MHz without GNSS	RCC, after the system computes a position	Can take longer and is less precise
121.5 MHz homing	Aircraft and rescue units close in	Final approach only
AIS (EPIRB-AIS models)	Nearby ships and aircraft with AIS	Shown on their AIS displays

Activation and release

On a SOLAS ship the EPIRB sits in a float-free bracket. If the ship sinks, the hydrostatic release unit (HRU) cuts the beacon loose at a depth of a few metres, the beacon floats up and switches itself on. That covers the case where the ship goes down too fast for anyone to act.

Do not wait for that if you need help sooner. If you are abandoning ship, take the beacon out of the bracket, activate it by hand following the marked procedure, take it into the liferaft and tie it to the raft, not to the ship. Keep it upright, with the antenna clear of the canopy.

A deliberate beacon workflow

1Decide whether you need help now. If yes, alert by every means available; the EPIRB is one of them.
2Free the beacon by hand, or let the HRU release it if the ship sinks.
3Activate it using the marked procedure and check the indicator light.
4Keep it in the open, upright and secured to the liferaft.
5Listen on the survival-craft VHF for rescue units, and give details by voice when you can.

If the beacon goes off by accident, switch it off and tell the nearest RCC or coast station at once: beacon identity, position, time of activation and that there is no distress. Then log it. Putting it back in the bracket without telling anyone leaves an RCC searching for a ship that is fine.

Worked insight: alerting is not the whole rescue

At 0300 a ship sinks quickly in heavy weather. The HRU frees the EPIRB at about 4 m, it surfaces, and its GNSS position is in the first burst. The RCC may have it within minutes and calls the registered owner, who confirms the ship is on that route. An aircraft is sent, but the EPIRB cannot tell it there are 18 survivors in two rafts with one injured. The survival-craft VHF and the SART do that work.

Keep up the maintenance that makes the alert useful: a monthly self-test, an annual test, shore-based maintenance at least every 5 years, HRU replacement at its expiry date (typically 2 years) and up-to-date registration. The IMO EPIRB performance standard MSC.471(101) sets what an approved SOLAS beacon must do. A leisure beacon may have fewer features.

Official references · 2026-09-09

MSC.471(101) · MSC.514(105) · NOAA beacon identifiers