Are EPIRBs dead?

[Wotname]

Originally Posted by estarzinger

…………..
And on a prior topic of debate, not only can USCG assets home on 406 signals (as you all eventually agreed), but they can also in fact de-code and read the signals directly on board - so if it's a g-Epirb they are directly getting the real time location bursts and updating their waypoint.

I can't comment accurately on what the USCG assets are capable of but for readers outside the USA, I can add that this is not universal. In fact it can even vary in a single location. For instance, in Australia (and at single city), some SAR aircraft have 406 receivers with decoders, some only have receivers and some don't have any 406 equipment on board.

Luck of the draw if the best one is in the hangar for maintenance, you will get the next best

[transmitterdan]

Does anyone know when the ACR SARlink device will be for sale? This looks pretty interesting. It is a PLB and an Iridium SEND in one handheld unit. The Iridium radio is rechargeable and the PLB has a dedicated battery.

[hellosailor]

If I remember correctly the USCG was still using the old Sea King helos at Floyd Bennett Field in the 1980's and 1990's, partly because they were (supposedly) the only ones available with explosive guillotine cutters to drop the hoist line in case of emergency. And the crews had so much faith in them, that they ran belly lines under the helos in case they had to make a water landing--in which case, they'd have a line to climb UP onto the inverted hull.


Anyway, these and a lot of other USCG assets had individually purchased GPSes stuck onto the console for many years, while the USCG and the GPS makers thought about whether a GPS has any real use, whether it was worth getting them FAA certified, and whether the USCG really wanted to spend any money on old aircraft instead of scrimping it up for new ones that MIGHT have the stuff built in.


Just saying, historically? The USCG is the youngest sibling that gets the hand-me-downs and leftovers, and just because the equipment would be useful, doesn't mean anyone authorized having it installed.

[Rustic Charm]

Originally Posted by estarzinger

Well, don't bang your head too hard, because in fact some type II models ("manual" Not hydrostatic) do salt water activate. They have two exposed pan head screws on the base or side, and if there is a salt water connection across those screws they activate. This specifically happened in the low speed chase incident - the Epirb got wet in the knockdown and fired off without being manually activated. Both ACR and McMurdo have type II models which do this. They both also sell brackets with built in magnets which hold reed switches open so they will not fire when wet, unless manually released from the housing.

This is copied out of a McMurdo type 2 users manual : "The two studs on the sides of the EPIRB are sea switch contacts. Submerge these in water to activate the EPIRB automatically." http://www.mcmurdomarine.com/images/...Murdo%20V2.pdf

I was NOT suggesting you can't get them as an automatic activation. Read my post!

[Dockhead]

Originally Posted by Wotname

I can't comment accurately on what the USCG assets are capable of but for readers outside the USA, I can add that this is not universal. In fact it can even vary in a single location. For instance, in Australia (and at single city), some SAR aircraft have 406 receivers with decoders, some only have receivers and some don't have any 406 equipment on board.

Luck of the draw if the best one is in the hangar for maintenance, you will get the next best

That's my understanding as well.

To decode the data burst from a 406 beacon, you need different equipment -- something like the Becker BD406, which has only been on the market for a couple of years and which is not common yet.

"The new BD/PBD406 provides an immense improvement in identifying the precise location of a distress beacon when compared to older direction finding systems, in addition to a much lower hardware cost.”

As we've discussed, the continuous 121.5 mhz signal is specifically designed for homing, and homing on this signal is still the primary method for guiding into the last mile. Homing on the 406 mhz signal, which is emitted in bursts, and which is not received by most equipment, is not that common, but maybe useful if for some reason you need to home from a longer distance (406 beacon with no GPS; faulty GPS in the beacon; faulty comms to SAR headquarters).


Direct decoding of the beacon data bursts -- especially now that GNSS receivers have become so precise -- would be the killer app, I guess, better than any kind of radio direction finding. But remember that adoption of new technology comes slowly in institutions like SAR services, because every change in technology requires training of hundreds of people and revision of protocols.

[estarzinger]

Originally Posted by Rustic Charm

I was NOT suggesting you can't get them as an automatic activation. Read my post!

What I am telling you is that a surprising number of "manual" models - type II, not hydrostatic release - in fact have these salt water studs, and a lot of owners don't know it. I had what I thought was a purely manual ACR Epirb, it was a low end model, with nothing obviously "automatic" or "water activated" in the marketing material. But after I was on the low speed chase investigation panel, and learned that many such units had these salt water studs, I looked and low and behold mine did also.

So, I am suggesting this will be news to a lot of owners, perhaps even you. The Low Speed Chase Crew did not know theirs would water activate, and neither did I until after that incident.

Dockhead, regarding 121 homing (http://www.sarsat.noaa.gov/BMW%2008%...2008%20BMW.pdf)

"When initially developed, the electronic signal from a factory EPIRB or
ELT emanated at 75 milliwatts on the 121.5 frequency. The electronic
detection equipment installed on CG aircraft at that time was sufficient to
detect this signal.
However, the FCC subsequently mandated that the power be reduced to
25 milliwatts on the 121.5 MHz homing signal due to interference at the
higher power on aircraft emergency frequencies.
Unless in very close proximity (less than 5 NM), this lower 25 milliwatt
power falls below the threshold of effective detection with the legacy CG
aircraft DF equipment."

[estarzinger]

^^ here are some direct notes from an interview after a fishing boat rescue:

"The 406 DF equipment work extremely well. Once we got up into the Class "A" airspace (above 18,000') we were picking up multiple DF hits. At about 150
nm's out, we got a solid lock.

The weather on scene when we initially got there was really crappy...night time, low ceiling, lightning in the vicinity, about 60-65 knot winds, and at least 8 ft seas. We weren't able to locate the strobe on the first pass. We did get a good needle swing and marked the associated position. With the next couple of passes we positively identified the strobe on the beacon...maybe 15 minutes total into the sortie.

The 121.5 was very very weak...only being audible for a period of a few seconds when we were directly overhead."

[transmitterdan]

That's ok because the helo should be able to get within 5km just knowing the coordinates. Even without coordinates a 4kM search grid can cover a lot of area in a hurry. Much faster than eyeball scanning.

But the second device you want in the ditch bag is a DSC handheld with replaceable batteries. When you hear or see the helo hit the DSC distress button. Their VHF radio should light up and squawk and they will see your coordinates.

[Dockhead]

Originally Posted by estarzinger

^^ here are some direct notes from an interview after a fishing boat rescue:

"The 406 DF equipment work extremely well. Once we got up into the Class "A" airspace (above 18,000') we were picking up multiple DF hits. At about 150
nm's out, we got a solid lock.

The weather on scene when we initially got there was really crappy...night time, low ceiling, lightning in the vicinity, about 60-65 knot winds, and at least 8 ft seas. We weren't able to locate the strobe on the first pass. We did get a good needle swing and marked the associated position. With the next couple of passes we positively identified the strobe on the beacon...maybe 15 minutes total into the sortie.

The 121.5 was very very weak...only being audible for a period of a few seconds when we were directly overhead."

As I wrote, the burst transmission on 406, which is transmitted at 5 watts, will work better for RDF homing at long ranges, like 150 miles in this case. Great in case you don't have position coordinates from GPS, or you lost comms to SAR headquarters, etc. The 121.5 homing signal is not intended for long range -- it's only a few milliwatts. It's intended for the last mile or last few miles.

But RDF homing from long range is not protocol. You would do it only if there is some problem in the normal procedure. Even if the beacon is not transmitting position data, the satellites will give a position accurate to a couple of miles by doppler and triangulation (as the old system did with the old beacons). Standard procedure is to go to that position and THEN start RDF homing using 121.5. "That position" should be within a few cables if the system is working correctly, or at worst within a couple of miles. By that time you will really prefer to use the 121.5 signal specifically intended for this purpose, which is emitted continuously. Not the 406 burst transmission which is emitted only for half a second, every 50 seconds. And which most SAR equipment doesn't even receive, anyway.

It could be that some EPIRBS don't emit the 121.5 signal very well for some reason. Or the antenna is obscured by something, or tilted at the wrong angle, so that you can only receive it from directly overhead. Of course if you have some other means of RDF homing as a backup, like homing on the 406 signal, this is only good. Or best of all, direct decoding of the 406 burst data. The more means of finding the casualty you have, the better, obviously.

[Wotname]

Originally Posted by estarzinger

What I am telling you is that a surprising number of "manual" models - type II, not hydrostatic release - in fact have these salt water studs, and a lot of owners don't know it. I had what I thought was a purely manual ACR Epirb, it was a low end model, with nothing obviously "automatic" or "water propagandain the marketing material. But after I was on the low speed chase investigation panel, and learned that many such units had these salt water studs, I looked and low and behold mine did also.....

This is quite interesting, especially as the marketing information failed to mention the feature. Presumably the operation manual also fails to mention it.

If it was my unit, I would be very suspicious and would want confirmation that the unit was actually water activated. My first thought would be that they used the same case for various models and as mine was the low end model, the internal water switching circuitry would be absent rather than simply being left out of the marketing propaganda.

[Rustic Charm]

Originally Posted by estarzinger

What I am telling you is that a surprising number of "manual" models - type II, not hydrostatic release - in fact have these salt water studs, and a lot of owners don't know it. I had what I thought was a purely manual ACR Epirb, it was a low end model, with nothing obviously "automatic" or "water activated" in the marketing material. But after I was on the low speed chase investigation panel, and learned that many such units had these salt water studs, I looked and low and behold mine did also.

So, I am suggesting this will be news to a lot of owners, perhaps even you. The Low Speed Chase Crew did not know theirs would water activate, and neither did I until after that incident.t."

Yes, that is interesting. There usually referred to 'water activated'. I'm not at all sure why they are called 'manual' if they are indeed designed to be 'set off' automatically when exposed to water. I'm also not to sure how many are out there like that as doing a rough Google search is a struggle to get much if a result. GME produce one. But again, roughly twice the cost of a manual non water activated one. Acr also produce one which is a standard price.

The one thing for sure though, I'm sure you would agree, is that the owner/and users should know how to use them before they need to use them.

In the 90's a police launch I used to use had an early model Epirb which you needed to do two things. Firstly you had to attach the Ariel to it as it was kept in a bracket on its side. The second thing was to break off a plastic cover in order to then expose the switch which was activated when thrown into the water. Similar sort of thing.

[transmitterdan]

A common problem is people think the "manual" units are activated by some switch. Most units have to be floating in the water to activate.

The "manual" part is removing the unit from the holder and putting it in the water. The rest is automatic.

[hellosailor]

The purpose of a unit being both "manual" and "water activated" is that it allows you to punch the button, turn it on, and KEEP THE EPIRB ON THE BOAT or in the liferaft with you.


Adding water activation is there mainly in case you, the boat, and the EPIRB somehow wind up swimming without a lifeguard. Unlike the Holy Hand Grenade, you do not want to pull the pin and TOSS the EPIRB, since it might be fouled, eaten, or simply drift away in the wrong direction.


A nice backup means of activation, but I'd rather have the EPIRB relatively high and dry, with me, and not take a chance it was going to leak and flood and die in the water.


I suspect the water activation circuit means there is always some part of the circuit that is on, even when it is "off", and draining some tiny amount of power all the time as well. Dunno.

[socaldmax]

Originally Posted by Dockhead

As I wrote, the burst transmission on 406, which is transmitted at 5 watts, will work better for RDF homing at long ranges, like 150 miles in this case. Great in case you don't have position coordinates from GPS, or you lost comms to SAR headquarters, etc. The 121.5 homing signal is not intended for long range -- it's only a few milliwatts. It's intended for the last mile or last few miles.

But RDF homing from long range is not protocol. You would do it only if there is some problem in the normal procedure. Even if the beacon is not transmitting position data, the satellites will give a position accurate to a couple of miles by doppler and triangulation (as the old system did with the old beacons). Standard procedure is to go to that position and THEN start RDF homing using 121.5. "That position" should be within a few cables if the system is working correctly, or at worst within a couple of miles. By that time you will really prefer to use the 121.5 signal specifically intended for this purpose, which is emitted continuously. Not the 406 burst transmission which is emitted only for half a second, every 50 seconds. And which most SAR equipment doesn't even receive, anyway.

It could be that some EPIRBS don't emit the 121.5 signal very well for some reason. Or the antenna is obscured by something, or tilted at the wrong angle, so that you can only receive it from directly overhead. Of course if you have some other means of RDF homing as a backup, like homing on the 406 signal, this is only good. Or best of all, direct decoding of the 406 burst data. The more means of finding the casualty you have, the better, obviously.

You keep arguing this point about homing in on the 121.5 MHz signal. Why bother switching to a lower power signal when you've already been flying directly toward the contact for 150 mi?

Hell, by the time they pick up a 25mw signal, they can see the whites of their eyes. At night. In dense fog.

Rather than continuing to make assertions, let's see some info from the USCG that states they switch to tracking the 121 MHz signal, right about when they're close enough to smell them.

[socaldmax]

Originally Posted by hellosailor

The purpose of a unit being both "manual" and "water activated" is that it allows you to punch the button, turn it on, and KEEP THE EPIRB ON THE BOAT or in the liferaft with you.


Adding water activation is there mainly in case you, the boat, and the EPIRB somehow wind up swimming without a lifeguard. Unlike the Holy Hand Grenade, you do not want to pull the pin and TOSS the EPIRB, since it might be fouled, eaten, or simply drift away in the wrong direction.


A nice backup means of activation, but I'd rather have the EPIRB relatively high and dry, with me, and not take a chance it was going to leak and flood and die in the water.


I suspect the water activation circuit means there is always some part of the circuit that is on, even when it is "off", and draining some tiny amount of power all the time as well. Dunno.

The water activation circuit doesn't need to use any power, it's just an open circuit that gets completed, like a bilge sensor. Until the circuit is complete, no current flows.


That brings up another point, battery self discharge rate based on battery chemistry. Lipo batteries (I'm lumping the whole family of Li based batteries together) have a very slow self discharge rate, but they haven't been around for 35 yrs, so earlier EPIRBs must have used a different chemistry like NICAD, or NIMH.

Does anyone know what older EPIRbs used, and when they started using Li based batteries? I'm sure that increased reliability just because they wouldn't be discharged when you needed them. I can't imagine batteries from 35 yrs ago lasting 5 yrs baking in a sealed device without losing a great deal of it's charge.