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Sail-World.com : Rescue Beacons - detection times

Rescue Beacons - detection times

'Deployment of an EPIRB was instrumental in the rescue within hours of the crew of Groupama 3 from the Pacific Ocean' Groupama - Franck Cammas © Click Here to view large photo

Over recent years, the latest generation of 406Mhz Rescue Beacons have been gradually introduced. A total changeover to the new system was forced in February this year with satellites no-longer monitoring the older 121.5 / 243MHz versions.

406 EPIRB - photo by Connie Terrell, US Coast Guard - .. .

The new 406 system encompasses EPIRB’s (Emergency Position Indicating Radio Beacons) designed for marine use, PLB’s (Personal Locator Beacons) designed for tramping and other land activities and ELT’s (Emergency Locator Transmitters) designed for aircraft. All operate in the same way, they are just optimised for their designed use. NOTE: Most new PLB’s are waterproof and can be suitable for limited close to shore marine use.
Rescue beacons are also divided into GPS and non-GPS versions. The GPS version has a built in GPS resulting in quicker resolution of the position of the activated beacon. They are wonderful devices and have saved many lives.

This article discusses only one aspect of Rescue Beacons – that is the time taken to detect both sorts of 406 beacon (both GPS and non-GPS equipped beacons). There has been significant publicity stating that the non-GPS beacon will initially be detected in about 5 minutes but take longer to determine the position, while the 406 GPS beacon will be detected including an accurate position in around 5 minutes.

Both statements unfortunately can be quite wrong and to understand why we need a little understanding of satellites.

Two basic satellite types exist and both are used to receive and relay signals from rescue beacons:

LEO’s (Low earth orbiting) These are constantly orbiting around the world with one somewhere near New Zealand approximately once every hour. These were the satellites used for the redundant 121.5/243 type rescue beacons.

GEO’s (Geostationary) These are all located over the equator and sit in the same position relative to the earth at all times – the Optus Sky TV satellites are one example of this type (but are not used to detect distress beacons).

Sole survivor Nick Schuyler in a recent US boating incident clung to the upturned boat for 46 hours - they had no EPIRB on board. Three drowned. - .. .

Because the radio frequency transmitted by a Rescue Beacon travels in a straight line (does not refract), in order to get the rapid detection and position resolution that the new generation 406 Rescue Beacons are capable of, they must be able to 'see' (be line-of-sight with) one of the GEO satellites used by the Cospas-Sarsat Rescue Beacon system.

Only one GEO satellite covers New Zealand. It sits above a point around the mid-Pacific Ocean, with New Zealand near its western coverage extremity. This means to get rapid detection, you must be positioned to see a clear horizon towards the east-north-east. The actual bearing and angle above the horizon varies from the north to the south of New Zealand. In Auckland it is around 23 degrees above the horizon, but if we go to the west of Stewart Island it is only 11 degrees above the horizon. In Auckland the Sky TV satellite is about 44 degrees above the horizon!

If you cannot see the GEO, you will have to wait for a 'good' pass of one of the LEO’s. On the open sea, generally we can see a GEO with reasonable success but on land it can be a different story. Detection delays of over two hours are quite possible, but it will still work and can still save your life.

EPIRB process - .. .

The message – if you want to be located quickly, make sure you have a GPS equipped beacon and can see a good low horizon in the north easterly quarter. If you don’t have a clear view to the north-east, or more correctly east-north-east, don’t expect a rapid detection of your distress – it could be at least 2 hours before SAR authorities are aware of your situation and can start arranging rescue resources.

It is vital that all 406 beacons are registered – so that SAR authorities know who/what is in distress. 406 beacon registration is a free service and can be done on-line at www.beacons.org.nz

For more information on this and other marine safety issues check out the range of Coastguard Boating Education courses offered throughout New Zealand www.cbes.org.nz

by Martin Balch

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9:00 AM Wed 29 Jul 2009 GMT

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