Distress Beacons

A distress beacon is a small electronic device that can be manually activated in a life-threatening situation to transmit an emergency signal to search and rescue (SAR) authorities. The signal is picked up by the COSPAS-SARSAT satellite system and overflying aircraft which then report the beacons' position to the relevant land-based authorities.

There are 3 types of satellite distress beacons:

  1. Emergency Position Indicating Radio Beacons (EPIRB) used in ships and vessels;
  2. Emergency Locator Transmitters (ELT) used in aircraft; and
  3. Personal Locator Beacons (PLB) for use by individuals in a marine or land-based environment

EPIRBs, PLBs and ELTs currently operate on two frequencies - 406 MHz and 121.5 MHz. 406 MHz beacons use digital technology that allows the beacon to transmit a unique code (HexID or UIN) that identifies the beacon. Beacons that operate on 121.5 MHz use analogue technology and cannot be identified.

There are two basic types of 406 MHz beacons - those that provide an encoded GPS location and those that do not. The satellite system can calculate a beacon's location, but locating a distress site is usually much faster if the beacon signal provides a GPS location.

When a 406 MHz beacon signal is received, SAR authorities can retrieve information from a registration database. This includes beacon owner contact information, emergency contact information, and vessel/aircraft identifying characteristics. Having this information allows SAR services to respond appropriately.  However, around 95% of distress alerts are false alarms so if a beacon is properly registered, an alert can normally be resolved with a telephone call to the beacon owner using the encoded beacon identification.

As of 1 February 2009, the 121.5MHz signal will no longer be processed by the COSPAS-SARSAT satellite system.

Comparison Table

 

406 MHz Beacon
121.5/243 MHz Beacon
Signal

Digital: unique identification, registration data provides information on the owner/vessel or aircraft

Analog: no data encoded, higher false alert rate

Signal Power

5 Watts pulse

0.1 Watts continuous

Coverage

Global

Regional

Position Accuracy

Within 5 km (Doppler), 100m if GNSS (GPS) position is encoded in message

Within 20 km (Doppler only)

Alert Time

GEO1 alert within 5 minutes

Waiting time for LEO2 satellite pass 45 minutes average

Doppler Position Ambiguity

Resolved at first satellite pass

Two passes required to resolve position ambiguity

1 Geostationary or Geosynchronous - where satellites are positioned at a fixed point  approximately 35,786 kilometers (19,323 nautical miles or 22,241 statute miles) above the earth's surface directly above the equator.

2 Short for Low Earth Orbit - satellites mostly used for telecommunications that orbit the Earth between 400 and 1,000 miles above the Earth's surface. LEOs are not fixed in space in relation to the rotation of the earth and so must transfer data being transmitted from one satellite to another as they move in and out of range.

Links to Useful Sites:

http://beacons.amsa.gov.au/distress_beacons.asp for more information about 406MHz EPIRBS in Australia

http://www.cospas-sarsat.org/

http://beacons.amsa.gov.au/