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An EPIRB, or Emergency Position-Indicating Radio Beacon, is a distress beacon which broadcasts a signal on a distress frequency able to be picked up by satellites and aircraft. It indicates to search-and-rescue authorities that someone is in difficulty and requesting assistance in a particular location. EPIRBs has led to a number of successful rescues of bushwalkers in recent years, avoiding costly search-and-rescue operations.
Criteria for use
Users should realise that triggering a beacon will initiate a search. This means that their use should be restricted to situations that meet one of the following criteria:
1. someone's life is in danger,
2. a delay in getting a sick or injured party member to medical attention will lead to further serious injury, or
3. you are already long overdue and have good reason to believe that a search for you has already begun.
Limitations of the system
The COSPAS-SARSAT system (the worldwide system's official name) has a number of limitations. The principal one is to do with the time it takes to receive a signal. The 121.5/243mhz system, widely used on smaller and simpler beacons, does not immediately locate the source of the signal. Depending on where you are, it may be several hours before the signal's location is determined. There are two reasons for this: firstly, the satellite uses the doppler effect to determine the position of the beacon, which generate two possible positions; one real, one false. It requires a second orbit to determine which one of the signals has moved (the false signal) and which has not moved (the real signal). Secondly, the satellite requires a direct line-of-sight to both the beacon and a ground station, which may not occur for a couple of orbits. Additionally, the 121.5/243mhz system does not broadcast any identification information. although the newer 406mhz system can. Therefore, search and rescue authorities (in our case, AUSSAR and through them state S&R organisations) have no idea what the nature of the emergency is.
Phase out of 121.5mhz system
The current analogue 121.5mhz EPIRB (electronic position-indicating radio beacon) system is due to be phased out in 2009 and replaced by an individually-coded digital system operating at 406mhz. While 406mhz EPIRBs are available, they are still relatively expensive. EPIRBs are available for hire from a variety of outdoor stores in Victoria and Tasmania at reasonable rates.
There are penalties for misuse of EPIRBs.
EPIRBs are for use in life-threatening situations only; the standard to use when deciding to activate an EPIRB is, "will someone die or be seriously injured if I do not?". If a walk is sufficiently dangerous that a distress beacon is necessary rather than optional, you should consider carefully whether the walk is appropriate for your party.
Over-reliance on electronic devices is a potential cause of problems for a party which does not have the equipment and skills to do without that device. An obvious example of this is a party which sets off with a map and GPS but no compass or spare batteries. You should never rely solely on electronic devices if the safety of your party could be compromised by the failure of the device to work properly.
More information
Australian Maritime Safety Authority This site contains information on EPIRB satellite distress beacons
COSPAS-SARSAT Largely technical site for the International Maritime Safety Organisation, which runs the EPIRB satellite distress system
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