EMERGENCY POSITION-INDICATING RADIO BEACON

'Emergency Position Indicating Radio Beacons' (EPIRBs), 'Emergency Locator Transmitters' (ELTs) and 'Personal Locator Beacons' (PLBs) are tracking transmitters that operate as part of the Cospas-Sarsat satellite system. When activated, the beacons send out a distress signal that allows the beacon to be located (and in the case of newer beacons, identified) by the satellite system and/or Search and Rescue (SAR) aircraft and ground search parties who can in turn come to the aid of the concerned boat, aircraft, and/or persons. EPIRBs are a component of the Global Maritime Distress Safety System (GMDSS).
The terminology is broken down as follows:

★ 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 response capabilities (i.e. 911)
In the most general sense, the terms are interchangable, and EPIRB is the most frequently used term to describe all such beacons together.
The basic purpose of the emergency beacons is to get people rescued within the so-called "golden day"[1] (the first 24 hours following a traumatic event) when the majority of survivors can still be saved.
Between 1982 and 2002, these systems enabled the rescue of 14,700 people. As of 2002, there are roughly 82,000 registered beacons, and over 500,000 of the older unregistered type.
=General Description=
Most beacons are brightly-colored, waterproof, fit in a cube about 30 cm on a side, and weigh 2-5 kg. They can be purchased from marine suppliers, aircraft refitters, and (in Australia and the United States) hiking supply stores. The units have a useful life of 10 years, operate across a range of conditions (-40°C to 40°C), and transmit for 24 to 48 hours. As of 2003 the cost varies from US$139 to US$3000, with varying performances (see below).
Distress beacons transmit distress signals on the following key frequencies; the frequency used distinguishes the capabilities of the beacon:

★ 406 MHz (UHF) - a unique 15, 22, or 30 digit serial number called a Hex Code is transmitted for a quarter of a second once every 50 seconds to both the GOES satellites as well as to Cospas-Sarsat LEO (Low Earth orbiting (LEO)) satellites. 406 beacons will be the only beacons compatible with the MEOSAR (DASS) system.[2]

★ 121.5 MHz (VHF) - a simple analogue siren tone is transmitted continuously until the battery dies. This frequency is monitored by most commercial airliners as well as by Cospas-Sarsat (C-S). The Cospas-Sarsat system can only detect this type of beacon when a Low Earth orbiting (LEO) satellite is in view of both the beacon and a SAR LUT (satellite dish). These beacons are being phased out.

★ 243.0 MHz (UHF) - uses the same technology as 121.5 beacons, however, other than by Cospas-Sarsat, this frequency is only monitored by military aircraft and some Air Traffic Control (ATC) stations. These beacons are being phased out.
Although modern systems are significantly superior to older ones, even the oldest systems provide an immense improvement in safety, compared to not having a beacon.
=Phase Out of 121.5 & 243 Beacons=
Beginning in 2009, only 406 MHz beacons will be detected by the international Cospas-Sarsat satellite system. This affects all maritime beacons (EPIRBs), all aviation beacons (ELTs) and all personal beacons (PLBs).
The International Cospas-Sarsat System will cease satellite processing of 121.5/243 MHz beacons from 1 February 2009.
According to Cospas-Sarsat (often abbreviated C-S), the international organization responsible for the Search and Rescue (SAR) satellite system, all beacon owners and users should begin taking steps to replace their 121.5/243 MHz beacons with 406 MHz beacons as soon as possible. C-S recommends that beacon owners should consider purchasing a 406 MHz beacon when the battery on an older 121.5 MHz beacon needs replacing. Typically, batteries need replacing about every five years. The sooner a beacon owner upgrades, the better the service that the Cospas-Sarsat System can provide in case the beacon is activated in a distress event.
More information about the switch to 406 is available on Cospas-Sarsat's 121.5/243 Phase-Out page.
Despite the switch to 406, pilots and ground stations are encouraged to continue to monitor for transmissions on the emergency frequencies, as many 406 beacons are also equipped with 121.5 'homers.' Furthermore, the 121.5 MHz frequency continues to be used as a voice distress frequency (especially in aviation.)
=SAR Response to Various Beacons=
Emergency beacons operating on 406 MHz transmit a unique 15, 22, or 30 character serial number called a Hex Code. When the beacon is purchased the Hex Code should be registered with the relevant national (or international) authority. Registration provides Search and Rescue agencies with crucial information such as:

★ phone numbers to call,

★ a description of the vessel, aircraft, vehicle, or person (in the case of a PLB)

★ the home port of a vessel or aircraft

★ any additional information that may be useful to SAR agencies
Registration information allows SAR agencies to start a rescue more quickly. For example, if a shipboard telephone number listed in the registration is unreachable, it could be assumed that a real distress event is occuring. Conversely, the information provides an quick and easy way for the SAR agencies to check and eliminate false alarms (potentially sparing the owner of the beacon thousands of dollars in negligent false alert fines.)
An unregistered 406 beacon still carries some information, such as the manufacturer and serial number of the beacon, and in some cases, an MMSI or aircraft tail number. Despite the clear benefits of registration, an unregistered 406 beacon is very substantially better than a 121.5/243.0 beacon; this is because the Hex Code received from a 406 beacon confirms the authenticity of the signal as a real SAR alert.
Beacons operating on 121.5 and/or 243.0 MHz simply transmit an anonymous siren tone, and thus carry no information to SAR agencies. Such beacons implicitly rely on the doppler location detection system. SAR authorities have no way of knowing whether a 121.5/243.0 MHz signal is actually a SAR signal until they physically deploy to the location and home in on the source (and sound) of the transmission. Since SAR resources are scarce (and expensive), most countries do not deploy the most useful SAR homing assets (aircraft) until ambiguity has been resolved (see doppler).

Contents

Responsible Agencies

Registration

Environment Specific Requirements

Aviation (ELTs)

Marine (EPIRBs)

Personal Locator Beacons (PLBs)

Current types

EPIRBs (marine)

ELTs (aircraft)

PLBs

Obsolete types

Obsolete EPIRBs

Obsolete ELTs

Obsolete PLBs

GPS-based, registered

High-precision registered

Traditional ELT, unregistered

Location by Doppler (without GPS)

Responsible Agencies

In the U.S., offshore beacons are investigated and victims rescued by the Coast Guard. On-shore beacons are investigated by local search and rescue services in Alaska. The Air Force Rescue Coordination Center is charged with land-based emergency signals, usually dispatching volunteer members from The United States Air Force Auxiliary Civil Air Patrol. In the U.S. there are no published notification systems for other locations.
=Statutory Requirements=
In the U.S. (as in most jurisdictions) no special license is required to operate an EPIRB. The following paragraphs define other requirements relating to EPIRBs, ELTs, and PLBs.

Registration

All distress alerting beacons operating on 406 MHz should be registered; all vessels and aircraft operating under SOLAS and ICAO regulations must register their beacons. Some national administrations (including the United States, Canada, Australia, and the UK also require registration of 406 MHz beacons.
The Cospas-Sarsat Handbook of Beacon Regulations provides the status of 406 MHz beacon regulations in specific countries and extracts of some international regulations pertaining to 406 MHz beacons.
The following list shows the agencies agencies accepting 406 beacon registrations by country:

★ United States - NOAA

★ Canada - NSS for civil beacons, CMCC for military beacons

★ Australia - AMSA

★ the United Kingdom - United Kingdom Mission Control Centre (UKMCC)

★ International - Cospas-Sarsat International 406 MHz Beacon Registration Database (IBRD)

Environment Specific Requirements

Aviation (ELTs)

Most general aviation aircraft in the U.S. are required to carry an ELT, depending upon the type or location of operation, while scheduled flights by scheduled air carriers are not. However, in commercial aircraft, a cockpit voice recorder or flight data recorder must contain an underwater detection beacon.
As per 14 CFR 91.207.a.1, ELTs built according to TSO-C91 (of the type described below as "Traditional ELT, unregistered") have not been permitted for new installations since June 21, 1995; the replacing standard was TSO-C91a. Furthermore, TSO-C91/91a ELT’s are scheduled to phased out Feb 1, 2009 to be replaced by the 406 Mhz TSO-126 ELT, a far superior unit.[3]
Though monitoring of 121.5 and 243 MHz (Class B) distress signals by satellite is scheduled to cease in 2009, there is currently no upgrade of older ELT units mandated by the FAA for aircraft in the United States.

Marine (EPIRBs)

Most commercial off-shore working vessels with passengers are required to carry a self-deploying EPIRB, while most in-shore and fresh-water craft are not.
As part of the United States efforts to prepare beacon users for the end of 121.5 MHz frequency processing by satellites, the FCC has prohibited the use of 121.5 MHz EPIRBs as of January 1, 2007 (47 CFR 80.1051). See the United States Coast Guard (USCG) brief on the 121.5/243 Phase-out.

Personal Locator Beacons (PLBs)

Personal Locator Beacons operating on 406 MHz must be registered. PLBs should not be used in cases where normal emergency response exists (i.e. 911.)
=Categories and Types=
There are two categories of beacons: manually activated, and automatically activated. Automatic EPIRBs are water activated, while ELTs are G-force (impact) activated. Some EPIRBs also deploy; this means that they physically depart from their mounting bracket on the exterior of the vessel (usually by going into the water.)
For a marine EPIRB to begin transmitting a signal (or "activate") it first needs to come out of its bracket (or "deploy"). Deployment can happen either manually - where someone has to physically take it out of its bracket - or automatically - where water pressure will cause a Hydrostatic Release Unit to release the EPIRB from its bracket. If it does not come out of the bracket it will not activate. There is a magnet in the bracket which operates a reed safety switch in the EPIRB. This is to prevent accidental activation when the unit gets wet from rain or shipped seas.
Once deployed, EPIRBs can be activated, depending on the circumstances, either manually (crewman flicks a switch) or automatically (as soon as water comes into contact with the unit's "sea-switch".) All modern EPIRBs provide both methods of activation and deployment and thus are labelled "Manual and Automatic Deployment and Activation."

Current types

EPIRBs (marine)

Current marine EPIRBs are generally divided into three classes; ''Category I'', ''Category II'',
and ''Class B'' (or ''Category B'').

★ ''Category I'' EPIRBs are considered the best but are also the most costly. The ''Category I'' - type is recommended by the IMO because a float-free bracket will deploy automatically once the vessel sinks and the EPIRB will then be activated automatically by immersion in water in the event of a disaster at sea. These EPIRBs are generally housed in a specially designed bracket on deck and the buoyant beacon is designed to rise to the surface and emit two signals, an emergency homing signal on 121.5 MHz and a digital identification Hex Code on 406 MHz that can be used to almost-immediately alert SAR authorities of the distress of the stricken vessel. ''Category I'' EPIRBs used in American waters must be registered with NOAA.

★ ''Category II'' EPIRBs are similar to ''Category I'' EPIRBs but are generally manual deployment only. Also like ''Category I'' EPIRBs, ''Category II'' units must be registered. ''Category II'' EPIRBs are also generally less costly averaging less than US$1,000.

★ ''Class B'' EPIRBs, also called ''Category B'' or ''"Mini B"'', operate a 121.5 MHz homing signal only and are usually manual deployment only units. They are the cheapest units but also the least capable. Since the signal has no identification component, Class B EPIRBs are not registered. Due to their limitations, ''Class B'' EPIRBs are slowly being phased out. As the International Cospas-Sarsat program will no longer monitor ''Category B'' EPIRB signals as of February 1, 2009, this type of beacon will become nearly useless. Although the U.S. Coast Guard no longer recommends them, they remain in wide use.

ELTs (aircraft)

ELTs used in aircraft are of the following types:

★ The new 406 Mhz TSO-126 ELT will be the only type of ELT detected by Cospas-Sarsat after February 1, 2009.
Types Being Phased Out:

★ TSO-C91 - 121.5 / 243 MHz unregistered - have not been permitted for new installations since June 21, 1995;

★ TSO-C91a - 121.5 / 243 MHz unregistered - was the replacing standard; most current aviation ELTs are of this type.

PLBs

All PLBs must have a Hex Code on the body. Persons must register this Hex Code with their national SAR agency. See below for types of PLBs no longer used.

Obsolete types

Obsolete EPIRBs

There are also several older types of EPIRB devices which are no longer recommended for use.

★ ''Class A'' - A 121.5 MHz automatic activation unit. Due to limited signal coverage and possible lengthy delays in signal recognition, the U.S. Coast Guard no longer recommends use of this type.

★ ''Class C'' - Operates on VHF channel 15/16. Designed for small crafts operating close to shore, this type was only recognized in the United States. Use of these units was phased out in 1999.

★ ''Class S'' - A 121.5 MHz unit similar to Class B but is often included as an integral part of a lifeboat or survival suit. Their use is no longer recommended by the U.S. Coast Guard.

★ ''Inmarsat E'' - entered service in 1997. The unit is an automatic activation unit operating on 1646 MHz and detectable by the Inmarsat geostationary satellite system. This class of EPIRB was approved by the Global Maritime Distress Safety System (GMDSS), but not by the United States. In September 2004, Inmarsat announced that it was terminating its ''Inmarsat E'' EPIRB service as of December 2006 due to a lack of interest in the maritime community.
Furthermore, the U.S. Coast Guard recommend that no EPIRB of any type manufactured before 1989 be used.

Obsolete ELTs

★ Any ELT that is not a 406 MHz ELT with a Hex Code will be obsolete February 1, 2009.

Obsolete PLBs

★ Military forces at one time used 121.5/243.0 MHz beacons such as the "PRQ-501," which had a built-in VHF radio. These are being replaced by modern 406 PLBs.
=How they work=
All the systems work something like this: A beacon is activated by a crash, a sinking, or manually by survivors. The beacon's transmission is picked up by one or more satellites. The satellite transmits the beacon's signal to its ground control station. The satellite's ground station processes the signals and forwards the data, including approximate location, to a national authority. The national authority forwards the data to a rescuing authority. The rescuing authority uses its own receiving equipment to locate the beacon and makes the rescue or recovery. Once the satellite data is in, it takes less than a minute to forward the data to any signatory nation.

There are several systems in use, with beacons of varying expense, different types of satellites and varying performance. Note that even the oldest systems provide an immense improvement in safety, compared to not having a beacon.

GPS-based, registered

The most modern 406 MHz beacons with GPS (US$ 1200-$3000 in 2002) locate a beacon with a precision of 100 meters, anywhere in the world, and send a serial number so the government authority can look up phone numbers to notify next-of-kin in four minutes, with rescue commencing shortly afterward. The GPS system permits stationary, wide-view geosynchronous communications satellites to enhance the doppler position received by low Earth orbit satellites. EPIRB beacons with built-in GPS are usually called GPIRBs, for GPS Position-Indicating Radio Beacon or Global Position-Indicating Radio Beacon.

High-precision registered

An intermediate technology 406 MHz beacon (US$ 500-900) has world-wide coverage, locates within 2 km. (12.5 km² search area), notifies kin and rescuers in 2 hours maximum (46 min avg.), and has a serial number to look up phone numbers, etc. This can take up to two hours because it has to use moving weather satellites to locate the beacon. To help locate the beacon, the beacon's frequency is controlled to 2 parts per billion, and its power is a hefty five watts.
Both of the above types of beacons usually include an auxiliary 25 milliwatt beacon at 121.5 MHz to guide rescue aircraft.

Traditional ELT, unregistered

The oldest, cheapest (US$ 139) beacons send an anonymous warble at 121.5 MHz. They can be detected by satellite over only 60% of the earth, require up to 6 hours for notification, locate within 20 km (search area of 1214 km²) and are anonymous. Coverage is partial because the satellite has to be in view of both the beacon and a ground station at the same time - the satellites do not store and forward the beacon's position. Coverage in polar and south-hemisphere areas is poor. The frequency is the standard aviation emergency frequency, and there is interference from other electronic and electrical systems, so false alarms are common. To reduce false alarms, a beacon is confirmed by a second satellite pass, which can easily slows confirmation of a 'case' of distress to up to about 4 hours (although in rare circumstances the satellites could be position such that immediate detection becomes possible.) Also, the beacons can't be located as well because their frequency is only accurate to 50 parts per million, and they send only 75-100 milliwatts of power.
These ELTs will not be monitored by Cospas-Sarsat after February 1, 2009.

Location by Doppler (without GPS)

When the beacon has no GPS receiver, the system locates the beacon from its doppler shift as received by the quickly-moving satellites. Basically, the frequency received varies depending on the speed of the beacon relative to the satellite. The amount of doppler is proportional to the range and bearing to the satellite. The instant the beacon's doppler shift changes from high to low indicates the time when the bearing from the beacon to the satellite's ground track is 90 degrees. The side of the satellite track is determined because the rate of change of the doppler is faster when the Earth is turning towards the satellite track.
In order to handle multiple simultaneous beacons, modern 406 MHz beacons transmit in bursts, and remain silent for a few seconds. This also conserves transmitter power.
Russia developed the original system, and its success drove the desire to develop the improved 406 MHz system. The original system is a brilliant adaptation to the low quality beacons, originally designed to aid air searches. It uses just a simple, lightweight transponder on the satellite, with no digital recorders or other complexities. Ground stations listen to each satellite as long as it is above the horizon. Doppler shift is used to locate the beacon(s). Multiple beacons are separated when a computer program performs a Fourier transform on the signal. Also, two satellite passes per beacon are used. This eliminates false alarms by using two measurements to verify the beacon's location from two different bearings. This prevents false alarms from VHF channels that affect a single satellite. Regrettably, the second satellite pass almost doubles the average time before notification of the rescuing authority. However the notification time is much less than a day.
=Operational Testing=
According to the FAA, ground testing of type A, B and S ELTs is to be done within the first 5 minutes of each hour. Testing is restricted to 3 audio sweeps. [4]
Type I and II devices (those transmitting at 406MHz) have a self test function and must not be activated except in an actual emergency.
The Coast Guard web page for EPIRBs states: "You may be fined for false activation of an unregistered EPIRB. The U.S. Coast Guard routinely refers cases involving the non-distress activation of an EPIRB (e.g., as a hoax, through gross negligence, carelessness or improper storage and handling) to the Federal Communications Commission. The FCC will prosecute cases based upon evidence provided by the Coast Guard, and will issue warning letters or notices of apparent liability for fines up to $10,000." [5]
=Satellites Used=
Receivers are auxiliary systems mounted on several types of satellites. This substantially reduces the program's cost.
The weather satellites that carry the SARSAT receivers are in "ball of yarn" orbits, inclined at 99 degrees. The longest period that all satellites can be out of line-of-sight of a beacon is about two hours.
The first satellite constellation was launched in the early 1970s by the Soviet Union, Canada, France and the USA.
Some geosynchronous satellites have beacon receivers. Since end of 2003 there are four such geostationary satellites (GEOSAR) that cover more than 80% of the surface of the earth. As with all geosynchronous satellites, they are located above the equator. The GEOSAR satellites do not cover the polar caps.
Since they see the Earth as a whole, they see the beacon immediately, but have no motion, and thus no doppler frequency shift to locate it. However, if the beacon transmits GPS data, the geosynchronous satellites give nearly instantaneous response.
=History=
The original impetus for the program in the U.S. was the loss of Congressmen Hale Boggs (D-LA) and Nick Begich (D-AK) in the Alaskan wilderness on October 16, 1972. A massive search effort failed to locate them. The result was a U.S. law mandating that all aircraft carry an emergency locator transmitter. Technical and organizational improvements followed.
Cospas-Sarsat is an international organization that has been a model of international cooperation, even during the Cold War. SARSAT means Search And Rescue SATellite. COSPAS is a Russian acronym with the same meaning. A consortium of Russia, the U.S., Canada and France formed the organization in 1982. Since then 29 others have joined.
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.
The U.S. Coast Guard once promoted an emergency beacon on maritime VHF emergency channels. It now promotes the superior Cospas-Sarsat system, and no longer services emergency beacons on maritime VHF frequencies.
=See also=

★ Civil Air Patrol (US Air Force Auxiliary)

★ Global Maritime Distress Safety System

★ Search and Rescue Transponder

★ GMDSS
=References=
COSPAS-SARSAT, Document C/S T.001 October 99
RTCM, Standard for 406 MHz Satellite EPIRBs
FCC, Part 80 and GMDSS
MED, 0735/2001
=External links=

★ Cospas-Sarsat - the International Satellite System For Search and Rescue

★ ITU - Maritime mobile Access and Retrieval System (MARS)

★ International Satellite System for Search and Rescue

★ NOAA SARSAT website

★ NOAA notice of planned phasing out of 121.5/243 MHz beacons in 2009