There are three types of beacons used to transmit distress signals, EPIRBs (for maritime use), ELTs (for aviation use), and PLBs (used for land-based applications). More information on these beacons is provided below.
Beacons are designed to transmit to satellites on either 121.5 or 406 MHz, although the 121.5 MHz beacons are now only used by the aviation community, and are being phased out. 406 MHz beacons can and should be registered. If for some reason a beacon activates inadvertently and it is registered, the Coast Guard or other rescue authorities can contact the owner and possibly avoid a costly and risky search. More importantly, registration will help rescue forces find persons in distress faster in an emergency.
Registration can be handled online at: http://www.beaconregistration.noaa.gov/ .
One common feature of all beacons is that in addition to their distress alerting signals, they transmit a low-power continuous 121.5 MHz signal that rescue units can home on to precisely locate them.
Some beacons are referred to as location-protocol beacons. The 406 MHz distress beacon message contains a beacon identification number, which is used by SAR personnel to identify a beacon owner and to initiate a preliminary location investigation. Approximately 30 percent of existing beacons incorporate a GPS navigation signal receiver into their design. These “location protocol” beacons can transmit their precise geographic location in addition to an identification number.
Emergency Position-indicating Radio Beacons (EPIRBs)
All authorized EPIRBs now operate on 406 MHz. The 406 MHz EPIRBs are divided into two categories. Category I EPIRBs are activated either manually or automatically. The automatic activation is triggered when the EPIRB is released from its bracket. Category I EPIRBs are housed in a special bracket equipped with a hydrostatic release. This mechanism releases the EPIRB at a water depth of 3-10 feet. The buoyant EPIRB then floats to the surface and begins transmitting. If you own a Category I EPIRB, it's very important that you mount it outside your vessel's cabin where it will be able to "float free" of the sinking vessel.
Category II EPIRBs are manual activation only units. If you own one of these, it should be stored in the most accessible location on board where it can be quickly accessed in an emergency.
A 406 MHz EPIRB signal can be instantly detected by geostationary satellites. This means that even a brief inadvertent signal can generate a false alert.
For more information on EPIRBs, see http://www.navcen.uscg.gov/marcomms/gmdss/epirb.htm.
Emergency Locator Transmitters (ELTs)
|Different types of ELTs are currently in use. There are approximately 170,000 of the older generation 121.5 MHz ELTs in service. Unfortunately, these have proven to be highly ineffective. They have a 97% false alert rate, activate properly in only 12% of crashes, and provide no identification data. To fix this problem 406 MHz ELTs were developed to work specifically with the Cospas-Sarsat system. These ELTs dramatically reduce the false alert impact on SAR resources, have a higher accident survivability rate, and decrease the time required to reach accident victims by an average of 6 hours.
General aviation aircraft must carry either a 121.5 MHz ELT or a 406 MHz ELT. One government study concluded that 134 extra lives and millions of dollars in SAR resources could be saved per year if these aircraft switched to 406 MHz ELTs, although these more effective ELTs cost more. For a comparison of 121.5 and 406 MHz beacons, see http://www.sarsat.noaa.gov/406vs121.pdf.
Most ELTs are designed to survive and activate automatically in a crash.
|Personal Locator Beacons (PLBs)
PLBs are portable 406 MHz units that operate basically the same as EPIRBs or ELTs, but are designed to be carried by an individual person instead of on a boat or aircraft. The number of these beacons in use has grown rapidly since they were authorized in July 2003. They can only be activated manually.
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