EPIRB (406 MHz)

What sets a 406 MHz EPIRB apart from other distress equipment

A 406 MHz EPIRB transmits a distress signal to satellites, giving rescue authorities a ship's identity and position with no action needed from anyone still able to reach the equipment — that is the entire point of the device, and it is what separates it from a SART, which does not alert anyone by itself but instead makes survivors visible to a searching vessel's radar once a search is already under way. An EPIRB works globally through the COSPAS-SARSAT satellite system; a SART works locally, within radar range of a searching ship or aircraft, and the two are carried together precisely because they cover different phases of a rescue.

Main components

Transmitter

Sends a coded 406 MHz burst to satellites, containing a unique identification number registered to the ship, and increasingly also transmits on 121.5 MHz as a homing signal for the final approach by rescue craft.

GPS receiver

Modern EPIRBs include an internal GPS module that encodes position into the distress message, cutting the time to an accurate fix compared with the older Doppler-only satellite method, which could take much longer and was far less precise.

Float-free bracket (hydrostatic release)

Releases the EPIRB automatically if the ship sinks before anyone can activate it manually, using a hydrostatic release unit that dissolves or releases under water pressure at a shallow depth.

Battery pack

Sealed primary battery with a fixed expiry date, sized to guarantee at least 48 hours of continuous transmission, and it is a one-time-use component — it cannot be topped up or reconditioned.

Selection and sizing

• Category I (automatic float-free release) versus Category II (manual release only), decided by SOLAS ship type and area of operation requirements rather than owner preference.
• GPS-integrated versus non-GPS models — GPS integration is now close to universal on new units and significantly reduces search time.
• AIS-equipped EPIRBs, which additionally transmit an AIS distress signal received by any AIS-fitted vessel within radio range, giving a much faster local response than waiting for satellite relay alone.
• Mounting location — clear of obstructions overhead so the hydrostatic release can actually let the unit float clear of a sinking hull.

Regulations and class

SOLAS Chapter IV (GMDSS) requires EPIRB carriage on all SOLAS cargo ships and passenger ships, with the specific category determined by ship type and trading area. The unit must carry COSPAS-SARSAT type approval, and the ship's identification data must be registered with the relevant national beacon registry — an unregistered or incorrectly registered EPIRB delays rescue coordination even if the transmission itself works perfectly. Battery and hydrostatic release unit expiry dates are checked at every annual GMDSS survey, and both are hard expiry items that class will not extend.

Typical faults

What to look for in a supplier

• Current COSPAS-SARSAT type approval and confirmation of which registry, flag state or a recognised alternative, the beacon ID will be registered under.
• Battery and hydrostatic release unit expiry dates clearly marked and matched to the ship's upcoming survey cycle.
• GPS and, where required by the operator, AIS integration confirmed rather than assumed.
• Bracket and mounting hardware suited to the specific deck location, since a poor mounting is a common cause of both false activation and release failure.

Confirm the beacon registration details every time the ship changes name, owner, or flag — a perfectly functioning EPIRB is only as useful as the registry record a rescue coordination centre pulls up when it activates.