Emergency position-indicating radio beacon


An emergency position-indicating radio beacon is a type of emergency locator beacon for commercial and recreational boats; it is a portable, battery-powered radio transmitter used in emergencies to locate boaters in distress and in need of immediate rescue. In the event of an emergency, such as a ship sinking or medical emergency onboard, the transmitter is activated and transmits a continuous 406 MHz distress radio signal, which is used by search-and-rescue teams to quickly locate the emergency and render aid.
The distress signal is detected by satellites operated by an international consortium of rescue services, COSPAS-SARSAT, which can detect emergency beacons anywhere on Earth transmitting on the distress frequency of 406 MHz. The satellites calculate the position or utilize the GPS coordinates of the beacon and quickly pass the information to the appropriate local first responder organization, which performs the search and rescue. As the search and rescue team approach the search areas, they use direction finding equipment to locate the beacon using the 121.5 MHz homing signal, or in newer EPIRBs, the automatic identification system location signal. The basic purpose of this system is to help rescuers find survivors within the so-called "golden day" during which the majority of survivors can usually be saved.
The feature distinguishing a modern EPIRB, often called GPIRB, from other types of emergency beacon is that it contains a GPS receiver and broadcasts its position, usually accurate within, to facilitate location. Previous emergency beacons without a GPS can only be localized to within by the COSPAS satellites and rescuers relied heavily upon the 121.5 MHz homing signal to pin-point the beacons location as they arrived on scene.
The standard frequency of a modern EPIRB is 406 MHz. It is an internationally regulated mobile radiocommunication service that aids search-and-rescue operations to detect and locate distressed watercraft, aircraft, and people.
The first form of these beacons was the 121.5 MHz ELT, which was designed as an automatic locator beacon for crashed military aircraft. These beacons were first used in the 1950s by the U.S. military and were mandated for use on many types of commercial and general aviation aircraft beginning in the early 1970s. The frequency and signal format used by the ELT beacons was not designed for satellite detection, which resulted in a system with poor location detection abilities and long delays in detection of activated beacons. The satellite detection network was built after the ELT beacons were already in general use, with the first satellite not being launched until 1982, and even then, the satellites only provided detection, with location accuracy being roughly. The technology was later expanded to cover use on vessels at sea, individual persons, and starting in 2016, maritime survivor locating devices. All have migrated from using 121.500 MHz as their primary frequency to using 406 MHz, which was designed for satellite detection and location, however most models still broadcast a secondary signal on 121.5 MHz as well, as this helps rescue teams pinpoint the location of survivors once in their vicinity with more accuracy than the 406 MHz frequency allows on its own.
Since the inception of COSPAS-SARSAT in 1982, distress radio beacons have assisted in the rescue of over 50,000 people in more than 7,000 distress situations. In 2010 alone, the system provided information used to rescue 2,388 persons in 641 distress situations.

Types of emergency locator beacons

The several types of emergency locator beacons are distinguished by the environment for which they were designed to be used:
  • ELT are carried on aircraft and are activated in the event of a crash.
  • * Activated by G-switch or manually by cockpit remote switch or ON switch on ELT.
  • EPIRB are carried on ships and boats, and signal maritime distress.
  • * Activated by water when the beacon is out of the bracket or manually by the ON switch on the EPIRB.
  • SEPIRB are EPIRBs designed only for use on submarines.
  • SSAS are used to indicate possible piracy or terrorism attacks discreetly on sea-going vessels.
  • * Activated by discreet switch/button in the ship's bridge or cabin, or manually on the SSAS.
  • PLB are carried by individuals and intended to indicate a person in distress who is away from normal emergency services; e.g., 9-1-1. They are also used for crew-saving applications in shipping and lifeboats at terrestrial systems. In New South Wales, some police stations and the NSW National Parks & Wildlife Service provide personal locator beacons to hikers for no charge.
  • * Activated manually by deploying antenna and pressing the ON button/switch.
Distress alerts transmitted from ELTs, EPIRBs, SSAS, and PLBs are received and processed by the International Cospas-Sarsat Programme, the international satellite system for search and rescue. These beacons transmit a 406 MHz distress signal every 50 seconds, varying over a span of 2.5 seconds to avoid multiple beacons always transmitting at the same time.
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 using the Doppler effect for trilateration, and in more recent EPIRBs, also by GPS.
Loosely related devices, including search and rescue transponders, AIS-SART, avalanche transceivers, and RECCO do not operate on 406 MHz, thus are covered in separate articles.

International COSPAS-SARSAT programme

is an international organization that has been a model of international cooperation, even during the Cold War. SARSAT means search-and-rescue satellite-aided tracking. COSPAS is an acronym for the Russian words "COsmicheskaya ''Sistema Poiska Avariynyh Sudov''", which translates to "space system for the search of vessels in distress". A consortium of USSR, the U.S., Canada, and France formed the organization in 1982. Since then, 29 other countries have joined.
The satellites used in the system include:
  • LEOSAR or Low Earth Orbiting Search and Rescue Satellites
  • * The LEOSAR system calculates the location of distress events using Doppler processing techniques. Doppler processing is based upon the principle that the frequency of the distress beacon, as "heard" by the satellite instrument, is affected by the relative velocity of the satellite with respect to the beacon. By monitoring the change of the beacon frequency of the received beacon signal and knowing the exact position of the satellite, the LUT is able to calculate the location of the beacon.
  • GEOSAR or Geosynchronous Earth Orbiting Search and Rescue Satellites
  • * As a GEOSAR satellite remains fixed relative to the Earth rotating with the earth around the equator, GEOSAR satellites utilize the GPS provided by the EPIRB, PLB, or ELT to provide rescuers with beacon position information.
  • MEOSAR or Mid-Earth Orbiting Search and Rescue Satellites
  • * The newest of the Cospas Sarsat satellites, detect EPIRB, PLB, and ELT distress signals in almost real-time including the beacons location with or without GPS.
  • * The new MEOSAR system also provides the framework along with the Galileo Global Navigation Satellite System for EPIRBs, PLBs, and EPIRBs to utilize the new Return Link Service or RLS that provides a confirmation message from Search and Rescue back to the beacon to let the survivors know their distress message was confirmed.
Cospas-Sarsat defines standards for beacons, auxiliary equipment to be mounted on conforming weather and communication satellites, ground stations, and communications methods. The satellites communicate the beacon data to their ground stations, which forward it to main control centers of each nation that can initiate a rescue effort.
Cospas Sarsat Monitoring include:
A transmission is typically detected and processed in this manner:
  1. The transmitter is activated, either automatically in a crash or after sinking, or manually by survivors of an emergency situation.
  2. At least one satellite picks up the beacon's transmission.
  3. The satellites transfer the beacon's signal to their respective ground control stations.
  4. The ground stations process the signals and forward the data, including approximate location, to a national authority.
  5. The national authority forwards the data to a rescue authority
  6. The rescue authority uses its own receiving equipment afterwards to locate the beacon and commence its own rescue or recovery operations.
Once the satellite data is received, less than a minute is needed to forward them to any signatory nation. The primary means of detection and location is by the COSPAS-SARSAT satellites. However, additional means of location are frequently used. For example, the FAA requires that all pilots monitor 121.500 MHz whenever possible, and the USCG has a network of direction finder sites along the coastlines. The National Oceanic and Atmospheric Administration maintains a near-real-time map that shows SARSAT U.S. Rescues.
Several systems are in use, with beacons of varying expense, different types of satellites, and varying performance. Carrying even the oldest systems provides an immense improvement in safety over carrying none.
The types of satellites in the network are:
  • LEOSAR
  • * Support Doppler detection and reception of encoded position
  • * Receivers are payloads on various Low Earth Orbit satellites
  • MEOSAR
  • * Medium Earth Orbiting Search and Rescue
  • * Receivers are payloads on the U.S. GPS satellites, on the Russian GLONASS satellites, and on the European GALILEO satellites.
  • GEOSAR
  • * Supports only reception of encoded position
  • * Receivers are payloads on various geosynchronous satellites, including some of the U.S. GOES weather satellites.
When one of the COSPAS-SARSAT satellites detects a beacon, the detection is passed to one of the program's roughly 30 Mission Control Centers, such as USMCC, where the detected location and beacon details are used to determine to which rescue coordination centre to pass the alert.