Some people have a lot of confusion about the use of EPIRBs and PLBs and the mechanisms by which they work.
Houston, We Have a Problem
Emergency beacons transmitting an SOS signal along with GPS coordinates became available in 1998. Initially, these emergency beacons transmitted on two frequencies: the more powerful 406 MHz signal, detectable anywhere in the world, and at a less powerful 121.5 MHz. The 121.5 MHz signal still offers some usefulness because rescue aircraft are often equipped with 121.5 MHz receivers, allowing them to home in on this signal once near the rescue location. Some devices today continue to use both frequencies, but a 121.5 MHz signal alone won’t be acted on by search and rescue unless it’s corroborated by two independent non satellite sources. Devices transmitted on 121.5 MHz only are forbidden to be sold or used in the United States.
Is Anybody Home?
International law established 406 MHz as an emergency-only transmitting frequency. Two major satellite networks are capable of receiving and relaying an emergency beacon on this frequency: The COSPAS-SARSAT constellation of satellites, an acronym for both search-and-rescue satellite-aided tracking and its Russian equivalent, is in a polar orbit over the North and South poles.
They were put in place as part of a joint effort that included the United States, Russia, Canada and France (where were the Brits, we wondered.) Knowing the position of the satellites when an emergency beacon is received allows search-and-rescue coordinators to narrow down a stricken vessel or occupant to within 2 to 5 kilometers. Sometimes, depending on the satellites’ location at the time of the beacon’s activation, closing the communication loop can take an hour or two.
A second group of satellites in geostationary orbit remain fixed above a particular spot on earth. These GEOS constellations include the GEOSTAR weather satellites. They can repeat an emergency beacon, but they can’t determine an exact location.
Location, Location, Location
Emergency Position Indicating Radio-beacons and Personal Locator Beacons — the latter is designed to be worn or carried by an individual, while the former is designed to be fitted to a vessel — have been equipped with the ability to transmit GPS coordinates with their SOS signal since 1998, giving search-and-rescue personnel a near-pinpoint location of the emergency. Today’s beacons also transmit vital information about the vessel or person wearing the device to aid in certifying the veracity of the emergency and to avoid expensive search-and-rescue efforts in case the SOS signal is an accident.
Don’t test your EPIRB or PLB by turning it on because it is against the law to do so. The law also requires SAR teams to respond to a beacon immediately. Recently, one fellow in the Florida Keys received a midnight call from the authorities verifying that his PLB pinging from the boat on his backyard hoist was an accident. Only 15 minutes earlier, rainwater had flooded the container of his PLB, activating it.
It’s important to note you are required to register your EPIRB or PLB. Registration permanently associates key information about the owner and the vessel. It also designates emergency contacts who can confirm the reported emergency and its GPS coordinates, speeding rescue.