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.
6Practice case & exam keys
Situation
A crewmember presses the EPIRB test control during a drill, then sees no rescue response and proposes activating it again.
What should the instructor reinforce?
Show the answer →
Use only the approved self-test and never repeat live activation to seek a response.
Why: A self-test checks the beacon according to its manufacturer procedure; it is not expected to create a distress case. A real activation is reserved for distress and starts an alerting chain. The crew should verify the test result, registration and readiness, and use a controlled training scenario for the remaining drill actions.
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.
7Full 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 an alerting beacon. Its 406 MHz transmission alerts the Cospas-Sarsat system, while a 121.5 MHz homing signal can help nearby rescue units locate the beacon. Modern approved EPIRBs may also provide GNSS and AIS locating functions, depending on the applicable standard and installation date. Registration, identity coding, battery status, hydrostatic release and national approval are practical parts of readiness.
Activation and release
The float-free arrangement is intended to release the beacon when the vessel sinks, but the crew must not wait for sinking if distress assistance is already needed. Keep the release unobstructed and do not secure the lanyard to the ship in a way that prevents separation. Once activated, follow the beacon’s operating instructions and keep it upright and visible as far as conditions permit.
| Signal or feature | Operational role |
|---|---|
| 406 MHz | Alerts the Cospas-Sarsat system. |
| 121.5 MHz | Supports local homing by suitable rescue equipment. |
| GNSS/AIS, where fitted | Adds locating information to the alert or nearby picture. |
A deliberate beacon workflow
- 1Decide whether the situation needs distress assistance now.
- 2Take the beacon from its assigned location or allow approved float-free release.
- 3Activate it using the marked procedure and move it clear of obstructions.
- 4Keep watch for rescue communications and use other available means to provide details.
- 5If activated accidentally, stop transmission only through the supported procedure, notify the RCC promptly with identity, position and time, and log the event.
Worked insight: alerting is not the whole rescue
An EPIRB alert can begin the rescue chain, but the crew still needs to communicate the situation, prepare survival equipment and follow instructions. GNSS availability improves location information but should not become a reason to delay a needed alert. A beacon’s signal, battery and antenna condition affect real performance, so readiness checks should examine context rather than promise one response time.
The beacon should be part of a wider abandonment plan: know who carries it, and keep approved battery, release and registration maintenance records current. Those details make the alert useful after it leaves the vessel.
The IMO EPIRB performance standard MSC.471(101) should be read with the vessel’s fitted equipment and manufacturer instructions. Do not infer that every recreational beacon has the same approval, registration or feature set as a SOLAS installation.
Official references · 2026-09-09
8Test your knowledge
Which system receives the 406 MHz alert?
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