I ordered a resq-fix a few days ago, and am expecting it to appear tomorrow, UPS willing.

I was talking about it at my local FBO and the owner of the FBO had some interesting comments on what he says is the procedure followed when you set off a 406 Mhz beacon. I don't know if he is correct or not, which is why I am writing.

He states that no SAR assets will be activated unless the SARSATs pick up two consecutive hits from the exact same location. He went on to say that if you pick up the beacon and move to the other side of the plane, the GPS location transmitted will change, so SAR activation will be delayed until the beacon is left in place for at least two sat passes. He further stated that if you move the beacon, the sats will ignore it until it is stationary for two passes again.

As stated above, I am asking if this is really the way it works.

I will remain happy with my purchase in either case, and hope, of course, that I never need to use it. But getting information on what happens after activation WILL effect HOW I use it, if G-d forbid I need to.

Thanks for your help.

Seth

If that's true, you'd be in bad shape if you were down in the drink. Even if you had a life raft, unless you could hold it dead still for 2 sat passes SAR would never respond.

FBO? Should that be added to the acronym list?

FBO = Fixed Base Operator. The business at an airport that provides services to General Aviation planes and pilots. They sell you fuel, maintenance, etc.

I agree with you, that you would be in real trouble in a raft, which is one of the things that prompted the question.

I received the beacon on Friday and, in reading the directions, see that its guaranteed battery life is 24 hours in temperatures from -4F to 130F, and at least 8 hours in temperatures between -40F and -4F.

My first thought was to keep it inside my parka if I need to activate it. Did I mention that I am going to take it to Alaska in December for some work I will be doing there? But the directions say that it should have a clear view of the sky, unobstructed by structure or clothing. They also warn against blocking it with your head while checking to see if the LEDs are flashing. So keeping it warm in my parka while it is operating looks to be out.

Does anyone have any suggestions for increasing the battery life, or, since it is reporting my Lat and Long, should I just not worry about it?

Thanks again

Seth

Hi Schaz,

To extend battery life in a field computer in the winter I have placed hand-warmer packs around the unit to keep it warm.

This should work with a PLB but I have never tried it.

Mike

There are two affects at work here.

1. A battery's self-discharge rate is lower at cooler temperatures. Storing a device in cool temperatures slows the loss of power over a battery's life.

2. The amount of energy that can be extracted from a battery goes up with higher (reasonable) temperatures. In other words, the amp-hours may be there, but the device may not be able to use them until the battery is warmed up.

The PLB can't be inside a parka or clothing when running. But if there is a motor running or some other source of heat perhaps the PLB can be atop it for warmth once activated.

I am puzzled as to what sort of batteries PLBs use. The operating temperature range and 5 year shelf life imply Lithium ... but I'd expect a 10-20 year shelf life in that case.

And the run time seems short ... if caught in a blizzard I'd be tempted to wait to hit the button until I thought SARS could get out so my beacon would still be running as they tried to close in on me.

Is a PLB the same as a 406mh PERB?

I listened to 2 interviews of the author of Lone Survivor.
He turned his military-PLB off to save batteries, when he was in
a poor locations. I believe he timed the "on" mode to satellite
position (overhead). He was also "on the move" so that might have
slowed his extraction.

I do not see the reasoning behind "not moving" criteria.
"He moved 400 yards in the last 4 hours so he must not need
help", is this an example of the SAR boss's reasoning?
Obviously, people, who are moving, can still need help.

I thought that a PLB may not always transmit position, for
example, a narrow canyon situation. But the position of the
satellite (receiver) or the position of the airplane (receiver),
in such a case, could be a starting point.

I call BS on the FBO.

One ping and the phone calls start to the numbers your registered when you went to the NOAA, website to see if you really may be in a situation to need help. If they cant confirm a false alert, the right folks are alerted.

Link to NOAA's FAQ page for further reading.

And a link for even more reading on how the system works.

I've heard of EPIRB (ship/boat), ELT (aircraft) & PLB (person). I don't know what a PERB is.

Great articles.

Thanks for your help.

Seth

It's my mistake.

I typed what I remembered from reading an earlier article, what I purchased is a PLB. Somehow I got the phrase Personal Emergency Rescue Beacon stuck in my head. So much for my memory.

Seth

I was on the SARSAT website today looking without success for formal beacon activation guidelines but did stumble across some information pertinent to beacon movement.

The SARSAT system sends regional centers one of several kinds of alerts when beacon activation is detected and continues to send them each above-horizon satellite pass until the incident is closed. Of interest:

- one message gives a satellite fix but states that the beacon ID information is not understood (for 406 Mhz). Even if they can't tell what or who you are the message is forwarded.

- the good position fix messages do tell the regional center if a satellite fixed the position or if the beacon supplied GPS data.

- if a satellite passes over a site and a signal was expected but not received the system sends an expected / not received message which regional centers receive.

- any position fix that differs from any previous position fix by more than 30 miles is specially flagged. I'm not sure what clears this flag: it seemed that any good fix by satellite or GPS would clear this.

There's nothing at the national Control Center about “two exact same location fixes”. SARSAT isn't that accurate: I think they get the GPS info tenths of an minute resolution, a few hundred feet at best (this is why ARC didn't bother to get ResQFIX's GPS accuracy better – there appears to be no way to send additional resolution even if they have it).

A consideration is that in many cases the estimated position will “move” thousands of feet at first. If a satellite position fix is made right away it will be sent through the system as a satellite fix. But the GPS will take some time to get a fix – 15 or more minutes – since it's cold started, meaning that only some later satellite pass gets GPS data. Since GPS fixes are so much better than satellite fixes that next pass may be a lot better than, and move some distance from, the first fix. It's possible that a regional center might look at a first message and see that it's satellite fix but know that the beacon manufacturer/model has internal GPS, and wait for a second satellite pass to get the GPS fix before launching SAR.

But the Control Center is going to keep sending the regional center updates every satellite pass, and if a regional center keeps simply ignoring them, with reports having good position fixes, good UID uploads and no reports of false beacon activation ... that regional coordinator is probably looking for a new job if Senator Jones' stepson owned that beacon.

As for comments in earlier messages:

- 406 MHz beacons definitely aren't good enough to tell what part of the plane you're in, even with GPS. The beacon can't give that kind of precision to the satellite as far as I can tell, even if the beacon knows.

- The satellites do not ignore any signals. Even gabled 406 MHz signals are sent to the Control Center, and policy says even unknown 406 MHz signals are sent to the regional centers if there is a satellite fix. The signal does need to be repeated correctly for the satellites to lock onto it but if the beacon sends stable garbage it's not the satellite that ignores it.

- If a position fix is on water I assume the regional center – Coast Guard? – won't be shocked to see subsequent fixes drift. They've done this before.

- Turning off a PLB during an alert seems unwise. It probably looks like a false activation being deliberately cancelled.

- In a very cold environment where the rated PLB runtime is reduced I'd try to wait until dawn to activate it. My concern is that SAR might not start at night since the odds of success are low and that environment is dangerous for SAR crews too. By activating at dawn you should still have batteries running for direction finding by the time SAR gets to you. If you activate at dusk and SAR doesn't launch until dawn you may be nearly out of beacon battery by the time SAR reaches your area.

Incidentally, there is only one system for these beacons, from PLBs up to commercial airplanes and cruise ships. It even appears that in some cases beacos for Navy subs (!) are routed through the national Control Center. The beacon's uplink data does indicate what kind of beacon it is, and of course registration data is on file, but the system itself it not segmented based on user type. PLBs are the same as the big boys as far as the satellites are concerned.

Others seem to have adequately answered most of your questions. To sum it up, the FBO owner doesn't know his butt from a hole in the ground when it comes to PLBs.

The replacment life of the lithium batteries is given at a conservative 1/2 their normal life, after taking into account all normal reduction in capacity over time including a self-test at the intervals recommended by the manufacturer, still alowing for a min. 24 hours run time at either -20 or -40 C, depending upon beacon class.

Turn on your PLB as soon as you determine you need help and leave it on.