EPIRB DELAYS

Submitted: Thursday, Jan 15, 2009 at 10:33
ThreadID: 65135 Views:2870 Replies:7 FollowUps:7
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Just reading about the new epirbs and came across this....
'The Australian Maritime Safety Authority warns that from February 1 the 121.5MHz EPIRBs would no longer be detected by satellite.

They would only be detected by aircraft still using that frequency, and then only if the plane flew directly overhead.

The 406MHz system has more power, provides rescuers with a more accurate location and notifies emergency services of a beacon activation within 90 minutes, as opposed to up to five hours on the old system.

90 minutes from the time u activate it....my question is..
why does that take so long???They work of satilites dont
they ??
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Reply By: timglobal - Thursday, Jan 15, 2009 at 11:58

Thursday, Jan 15, 2009 at 11:58
Darrell,

Yes they work using satellites, and the best have built in GPS for far reduced locating time.

However they still rely on orbiting satellites for triangulation / trilateration (unless you have GPS enabled one) so it depends on the vagaries of their changing position in the sky. They use geostationary satellites to receive alerts, but these can't locate you unless you have GPS, merely providing a first hit until the orbiting satellites pass over to locate - being up to 90 minutes.

A GPS enabled 406 EPIRB will, under almost all circumstances, provide a precisely located alert within seconds / minutes, with the slowest link here being the GPS getting hot and acquiring.

More info here US Coast Guard EPIRB site

Cheers,

Tim
AnswerID: 344410

Reply By: Member - MUZBRY(Vic) - Thursday, Jan 15, 2009 at 12:02

Thursday, Jan 15, 2009 at 12:02
Gday Darrell
When you activate your EPIRB, the call goes through to a call centre in Bombay, then to a person at 911, then they ask what state you are in, "quite perturbed i should think , or you would not have pressed the button".Then to someone in Canberra , then to the local person in charge of emergencies,who has to finish his tea,and then on they go to get you.Ther you go, 5 hrs..
Muzbry
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AnswerID: 344412

Follow Up By: Member - Kiwi Kia - Thursday, Jan 15, 2009 at 20:46

Thursday, Jan 15, 2009 at 20:46
MUZBRY, that is for the 'SPOT" beacons, not the 406 MHZ beacons.
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Reply By: howie - Thursday, Jan 15, 2009 at 12:27

Thursday, Jan 15, 2009 at 12:27
"They would only be detected by aircraft still using that frequency, and then only if the plane flew directly overhead"

sorry to keep on at this, but i have to correct things about planes & the 121.5.(not directed at you darrell)
IF a plane happened to be monitoring the 121.5 frequency, it MAY be able to detect it hundreds of miles away, not just overhead, depending on terrain and other things.
however, i just want to state that anyone still using a 121.5 epirb and expects every passing plane to pick up the signal is taking a big chance.
if you deem your mode of travel risky enough to have bought a 121.5 unit, surely you should upgrade to a 406mhz.(they could be cheaper IMHO)

in answer to your real question, it only takes seconds for the 406mhz to be received. that figure of 90 mins is for the 121.5mhz
analogue signal




AnswerID: 344416

Follow Up By: Member - Kiwi Kia - Thursday, Jan 15, 2009 at 20:44

Thursday, Jan 15, 2009 at 20:44
Sorry howie - not correct.

The following relates to a 406 MHz EPIRB that does NOT have a built in gps.

The 406 MHz alert signal is transmitted to a geostationary satellite and relayed to the nearest ground station (Canberra) almost instantly. However, to triangulate the signal and work out a very close ground position requires the 406 MHz signal to be picked up by TWO passing low orbit satellites. Depending on the latitude where the beacon is activated this could take up to 10 hours in a worst case scenario.

The first pass of a low orbit satellite will give TWO possible locations, one location either side of the satellite track over the surface of the earth.

The second low orbit satellite pass will also give two possible locations, one of which will be identical to one of the possible locations indicated by the first passing low orbit satellite. This 'matched' location is the position of the EPIRB.

The 406 MHz beacons also contain a 121.5 MHz transmitter and this signal is to aid searching aircraft to 'home in' as they approach the position derived from the two satellites.

So, the rescue centre will be alerted that an EPIRB has been activated and it's unique identifying number almost immediately. IF the beacon has been registered then from the identifying number they will also be able to ascertain the ownership of the beacon and details of the nominated persons who should know where the owner was planning to travel.

Now, back to the TWO possible earth locations of the activated beacon. If one of those possible positions is out in the Indian Ocean and the beacon is registered as being for land use then there is a very good chance that the land location is in fact where the beacon is located so the second pass of a low orbit satellite is only really a confirmation that the owner has not lent the beacon to a boatie mate who has taken out deep sea fishing.

.

.

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Follow Up By: howie - Thursday, Jan 15, 2009 at 21:24

Thursday, Jan 15, 2009 at 21:24
i did not say your position would be known in seconds, only the signal will be received in seconds.
the final positioning of the non gps beacon(within 5 miles) will be done by successive satellite passes as you say.

my main reason for posting is that there seems to be the idea, by people on this forum, they do not need to get the new 406mhz unit as every passing plane will come to their rescue.


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Follow Up By: Member - Kiwi Kia - Thursday, Jan 15, 2009 at 22:39

Thursday, Jan 15, 2009 at 22:39
Hi again Howie, I was referring to the following in your posting;

"in answer to your real question, it only takes seconds for the 406mhz to be received. that figure of 90 mins is for the 121.5mhz
analogue signal"

The 121.5 MHz transmission has nothing to do with 90 minutes. The 90 minutes may relate to the satellite passes only.

.
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Follow Up By: howie - Thursday, Jan 15, 2009 at 23:19

Thursday, Jan 15, 2009 at 23:19
we seem to be going down a path that i did not intend.
but, according to the amsa, the old 121.5 takes 90 minutes on average to be detected.
yes, that relates to satellite passes obv.

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FollowupID: 612483

Follow Up By: Member - Kiwi Kia - Friday, Jan 16, 2009 at 06:51

Friday, Jan 16, 2009 at 06:51
Howie, please also note that 'detected' does not mean located. It just means that a rescue center has been alerted that a beacon has been switched on somewhere.
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Reply By: The Rambler( W.A.) - Thursday, Jan 15, 2009 at 19:58

Thursday, Jan 15, 2009 at 19:58
The biggest delay is trying to get one--they are out of stock in most shops in WA.
Bush camp

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AnswerID: 344496

Reply By: slave - Thursday, Jan 15, 2009 at 20:32

Thursday, Jan 15, 2009 at 20:32
If you look at the new GME 406 epirbs you would see "quote" features a supporting 121.5 Mhz homing transmitter,so someone is still listening to this frequency, weather flying directly overhead or not.I think it has more to do with false alarms as the EPIRB is to be registered to a person/vessel
AnswerID: 344501

Follow Up By: Member - Kiwi Kia - Thursday, Jan 15, 2009 at 20:50

Thursday, Jan 15, 2009 at 20:50
Slave, the 121.5 signal will only be heard hundreds of km away if the aircraft is at very high altitude AND they are listening. The signal propagates outwards in an inverted cone shape (or funnel if you like).

.
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Reply By: Member - Graham H (QLD) - Friday, Jan 16, 2009 at 11:00

Friday, Jan 16, 2009 at 11:00
Dont know what all the fuss is about.

The new ones are obviously better.

The old ones may or may not be picked up by a hopefully in range plane.

You are stuck, out of water", food, everything including hope.

No good saying to yourself "Jeez wish I did buy that new EPIRB".

Just buy one if you feel you need one.
AnswerID: 344586

Reply By: Mogul - Friday, Jan 16, 2009 at 13:56

Friday, Jan 16, 2009 at 13:56
121.5 is an aircraft distress frequency so they will still be monitered.
AnswerID: 344612

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