Emergency Position Indicating Radio Beacons

#EPIRB 8 min 4229 views

Emergency Position Indicating Radio Beacons (EPIRBs) are small, portable, battery powered radio transmitters that are both watertight and buoyant and transmit in the 406.0 – 406.1 MHz channel. EPIRBs are carried aboard merchant ships, some private vessels, commercial and military aircraft. They also transmit a distinctive swept audio tone signal on the international aeronautical distress frequencies of 121.5 MHz for homing purposes by search and rescue aircraft. Aircraft at 30 000 feet can detect the audio tone signals at approximately 200 n miles. 

EPIRBs are tracking transmitters which aid in the detection and location of boats, aircraft, and people in distress. A PLB (personal locator beacon) is particular type of EPIRB that is typically smaller, has a shorter battery life and unlike a proper EPIRB is registered to a person rather than a vessel. The terms ELB (emergency locator beacon) and ELT (emergency locator transmitter) are used interchangeably with EPIRB only when used on aircraft. Strictly, they are radiobeacons that interface with worldwide offered service of Cospas-Sarsat, the international satellite system for search and rescue (SAR). When manually activated, or automatically activated upon immersion or impact, such beacons send out a distress signal. The signals are monitored worldwide and the location of the distress is detected by non-geostationary satellites doppler trilateration and in more recent EPIRBs also by GPS.

The basic purpose of a distress radiobeacon is to help rescuers find survivors within the so-called "golden day" (the first 24 hours following a traumatic event) during which the majority of survivors can usually be saved.



The 406 MHz EPIRB was designed to operate with satellites. The signal frequency (406 MHz) has been designated internationally for use only for distress. Other communications and interference, such as on 121.5 MHz, is not allowed on this frequency. Its signal allows a satellite local user terminal to accurately locate the EPIRB (much more accurately -- 2 to 5 km vice 25 km -- than 121.5/243 MHz devices), and identify the vessel (the signal is encoded with the vessel's identity) anywhere in the world (there is no range limitation). These devices are detectable not only by COSPAS-SARSAT satellites which are polar orbiting, but also by geostationary GOES weather satellites. EPIRBs detected by the GEOSTAR system, consisting of GOES and other geostationary satellites, send rescue authorities an instant alert, but without location information unless the EPIRB is equipped with an integral GPS receiver. EPIRBs detected by COSPAS-SARSAT (e.g. TIROS N) satellites provide rescue authorities location of distress, but location and sometimes alerting may be delayed as much as an hour or two. Although these EPIRBs also include a low power 121.5 MHz homing signal, homing on the more powerful 406 MHz frequency has proven to be a significant aid to search and rescue aircraft. These are the only EPIRB types which can be sold in the United States.

A 406 MHz EPIRB is a small, self–contained, battery operated radio transmitter which is both watertight and buoyant. 406 MHz EPIRBs are mounted in a special float-free bracket on either the bridge wing, or the compass deck. The hydrostatic release in the bracket is designed to release the beacon when the bracket is submerged to a certain depth.

Operating procedures differ between models, however all beacons incorporate a multi–position switch that selects the following modes of operation:

  •   Off (or safe) – the beacon is switched off , and will not transmit; 

  •   Armed (or auto) – the beacon will automatically switch on when it is released from the oat free bracket by the hydrostatic release mechanism; 

  •   On (or manual) – the beacon will switch on and transmit immediately; and 

  •   Test – activates a built in self-test routine.

Note: Some manufacturers recommend using the TEST function sparingly to maintain the battery life. Testing therefore should be done in accordance with the manufacturer’s user manual.

EPIRB Categories

Category I

406/121.5 MHZ. Float-free, automatically activated EPIRB. Detectable by satellite anywhere in the world. Recognized by GMDSS.

Category II

406/121.5 MHZ. Similar to Category I, except is manually activated. Some models are also water activated.


The type of a beacon is determined by the environment for which it was designed to be used:

- EPIRBs (Emergency Position Indicating Radio Beacons) signal maritime distress,
- ELTs (Emergency Locator Transmitters) signal aircraft distress
- PLBs (personal locator beacons) are for personal use and are intended to indicate a person in distress who is away from normal emergency services; e.g., 9-1-1. They are also used for crewsaving applications in shipping and lifeboats at terrestrial systems.

Additional EPIRBs

406 MHz beacons are also fitted in life-rafts on ships (replacing the 121.5 MHz beacons). These 406 MHz beacons are usually ‘Class 3’ beacons, i.e. manually-activated, non-float free. Although not required to be individually registered to a vessel like the SOLAS distress beacons, each beacon has a unique manufacturers serialised number, and liferaft servicing agents advise AMSA of the Class 3 beacons in the liferafts of each particular ship, to aid search and rescue.

GPS equipped EPIRBs

EPIRBs can also transmit a GNSS position provided it is fed from an internal or external GNSS device. If an internal GNSS receiver is fitted, these are sometimes known as “G-PIRBs”, but at the time of publication, were not mandatory on GMDSS vessels.

GpS versus non-GpS beacons - a GPS equipped beacon has a location accuracy of 120 m and location is provided by geostationary satellites within minutes. Non-GPS beacons have a location accuracy of 5 km. The satellite system takes 90 min on average to calculate the initial position from a beacon which is not GPS equipment, but it may take up to 5 h depending on the conditions. Considering that EPIRBs can be deployed from small survival craft in poor sea conditions, from a SAR perspective, GPS- equipped EPIRBS are recommended. 

Vessel Identification and beacon registration

Every 406 MHz EPIRB has a unique identity code which is transmitted as part of its signal. This code indicates the particular vessel and the country of beacon registration. This code is programmed into the beacon by the supplier before it is installed on board a vessel. Theoretically, LUTs anywhere in the world receiving a distress alert and location from an activated 406 MHz EPIRB can identify the vessel in distress and its country of registration. This is a great advantage for search and rescue planning, as each national MRCC holds a record of vessel characteristics such as; description, number of crew, etc.

If the system is to work successfully, and for their own safety, it is mandatory that purchasers of 406 MHz EPIRBs register their beacons. It is recommended that a copy of the registration form as submitted to the relevant beacon registration authority is available on board for inspection. An extract from IMO Resolution A.814 (19), Guidelines for Avoiding False Distress Alerts, states:

“...ensure that encoded identities of satellite EPIRBs, which are used by SAR personnel responding to emergencies, are properly registered in a database accessible 24 hours a day or automatically provided to SAR authorities (masters should con rm that their EPIRBs have been registered with such a database, to help SAR services identify the ship in the event of distress and rapidly obtain other information which will enable them to respond appropriately); ...”

Failure to do so is an o ence under Marine Orders. Purchasers of second-hand 406 MHz EPIRBs must also provide details to the database.

There is an international Beacon Registration Database for beacons coded to countries that do not have their own Registration Databases. 

The effectiveness of 406 MHz distress beacons is significantly improved when the beacons are properly registered and the registration information is available to search and rescue authorities. Search and rescue authorities have expressed concern that a number of national administrations do not have proper facilities to maintain and disseminate registration information.

In order to address those concerns, Cospas-Sarsat has made available the International Beacon Registration database (IBRD) system, operational from 16 January 2006 (www.406registration.com). 

Testing EPIRBs

406 MHz EPIRBs are subject to annual performance tests and shore-based maintanence. Marine Orders requires that a 406 MHz EPIRB is tested and, if necessary has its batteries replaced at intervals specified by the manufacturer. Hydrostatic releases must be replaced by their expiry dates. These are usually marked on the release mechanism. 

The EPIRB should be tested with special equipment - EPIRB Tester to verify its ID, as well as all technical parameters.


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