A couple of folks suggested bringing this topic over on its own, rather than continue to discuss on the accident thread. I am in agreement with that. Let's try to keep the ELT discussion over here.
This is long, but I think it contains important information on how these units function.
I just got off the phone with a fellow named Mick, who works for Cobham, Inc, the manufacturer of Artex ELTs. He was VERY informative and clarified a LOT of things for me, so here's his information:
1) Much of the information on how an ELT signal goes through the "system" that's posted on this site is WRONG. Here's the way it works, from an ELT designer:
The Beacon activates, and transmits a data burst every 50 seconds on a carrier wave, with an encoded data packet, into the atmosphere. That signal is picked up (assuming the antenna isn't broken, underwater, or????)within ten minutes by EITHER a polar orbiting satellite OR a geosynchronous satellite, and is transmitted down to a Local User Terminal (NOT RCC), of which there are ABOUT 10 to 12 world-wide. There are two in the US.
IF the initial data burst provides sufficient information and signal strength (strong enough, and maybe received by more than one satellite) the signal is passed along to the Rescue Coordination Center with jurisdiction over the LOCATION of the beacon.
If the signal isn't strong enough, or the triangulation isn't good enough for a position solution (not uncommon), the signal is passed to the country of origin for the beacon registration (NOT necessarily where the beacon hit came from in other words).
This goes to the MCC (Mission Control Center, NOT RCC) which decodes the data, searches the database, finds the contact info for the owner and makes the calls. THEN, if it is determined to be a REAL emergency, the information is transmitted to the RCC with jurisdiction and a SAR is initiated. By this time, HOPEFULLY, a better location will have developed, based on multiple satellite hits. Point is, if there is a "decent" general location initially, the system then knows which RCC to notify.
Note that, as I posted earlier, by the time a SAR crew is actually airborne or ready to launch, ANOTHER polar orbiting satellite will have passed, and refined the location better. So, by the time the CG/ANG/CAP/Troopers head out to actually search, the position of the ELT signal will have been refined more than the initial triangulation, BUT the system, without a GPS enabled ELT DOES NOT provide precisely accurate position location.
Finally, as the SAR element goes into action, they MUST search using the 121.5 signal, since the 406 signal transmits in momentary bursts every 50 seconds. There is NO way that you can DF on a 406 signal, which is why every 406 ELT and PLB and EPIRB has on board a 121.5 beacon as well.
Other points that Mick provided information on:
1) As I suspected, the new 406 ELTs are using the same G-switches as the old 121.5 beacons. So, the reliability of activation by switch hasn't and will not improve UNTIL the manufacturers get a solid state G-switch approved. Mick pointed out that this is a HUGE project, and adding a better switch will increase the cost of the units a LOT due to certification costs. Nevertheless, at present, the same switches are in use.
2) BUT, Mick then informed me that historically, 40 % of the ELTs that failed to activate (121.5 and 406) were torn from their mount in the accident sequence. This is apparently what happened in the Otter accident near Dillingham a few weeks ago, and by the way, Mick was the technician who disassembled and examined that ELT yesterday. In that case, the antenna cable was broken, so no signal was transmitted.
SOOOO, properly mounted, the current crop of ELTs would work 40 % more of the time (presumably) IF they were properly mounted. THAT is huge, and we should ALL give some consideration to that.
3) In the remaining cases where an ELT didn't activate, it turns out that the switches haven't been exercised annually, as part of the annual inspection of the ELT. This is recommended by the manufacturers, by the way. Never heard of this myself BUT..... Mick said that the problem is that the switch is a steel ball inside a cylinder, with springs holding it in position. If it's not exercised, it can seize up (my description, not his) or in any case, won't work. He says ALL ELT G-Switches should be exercised EVERY year. Write that one down, folks.
4) As I noted on the other thread, I spoke with RCC at Elmendorf, and, as I suspected, they gave me some incorrect information. In fact, the information that Beavercub got from RCC Coast Guard is also wrong in several points. Bear in mind that these are simply the folks who get the message and they aren't necessarily knowledgeable of the system's fine points.
Mick is VERY informed of the finer points of the system, since he designs ELTs to alert the system.
5) Advantages of the 406 beacons:
--They emit a MUCH stronger signal, since this is a digital signal and it goes out in bursts, as opposed to continuous as in the case of the 121.5 beacon.
--The 406 system triangulates similarly to the 121.5 beacons, but uses TWO layers of satellite systems instead of just one: a geosynchronous layer of satellites, AND a set of polar orbiting. In the days of 121.5 monitoring, the polar orbiting satellites monitored the 121.5 freq, and the geosynchronous monitored the 406 freq. So, NOW, the 406 has better satellite coverage, which will result in faster acquisition of a better, more accurate position, and often does.
--Nevertheless, initial position location for a 406 without a GPS interface is still 8 to 10 square kilometers at best. The accuracy for the 121.5 was 30 to 50 square kilometers. That's a huge advantage, no doubt, BUT the 406 CANNOT pinpoint a precise location of a beacon, regardless of the number of satellite hits .
--Some of the 406 ELTs are capable of connecting to a panel mounted GPS. At present, NO ELTs are capable of interfacing with a PORTABLE GPS. Cobham (Artex) is a couple weeks from releasing a NEW ELT that DOES offer a link to a portable GPS, via an NMEA connection port. He didn't give me a price, but it's not going to be cheap. The model number will be the Artex ME-183. I'll be looking at that one.
--As I suspected, ALL EPIRBS (the vessel version of the aircraft ELT) have onboard GPS units, which is how the 406 system can immediately and precisely locate a vessel that's sinking. Again, without the GPS interface, the initial 406 signal is still sort of vague, BUT it can get rescuers into close enough range so that they can home on the 121.5 signal.
I asked Mick why the ELT folks don't install GPS in ALL ELTs. His answer was that these boxes have to meet certification standards for ELT's, Comm devices, GPS, Antennas, AND mounting, etc. The GPS standards are especially difficult to meet, and so-----
both Kannad and Artex (the two largest manufacturers of ELTs in the world) are working on such units, but again, due to certification costs, they will be MUCH more expensive than the basic units. On the other hand, building such capability into an EPIRB for vessel use requires minimal certification.
I asked him about mounting protocols, and he noted that many manufacturers have mounting protocols for current production aircraft, and you can use that, or the mounting criteria are spelled out in the instructions. By the way, Mick is also an A & P mechanic, with 15 years experience in that field.
I also asked whether the velcro mounting straps used to secure both the Kannad and the Artex units are strong enough to meet the mounting standards. He said, essentially, that you can't believe how strong those velcro straps really are--they far exceed the 100 G standard.
Whew!!!! That was a looooong phone call, and very informative.
I'm now getting closer to the information that I've been looking for.
Seems like we can IMPROVE our chances of an ELT working by:
1) Ensure the mounting is STRONG
2) Exercise the G-Switch annually, by removing the unit, and shaking it to activate. Doesn't activate?? Get it fixed.
3) And, there are distinct advantages to the 406 beacons, which I recognized to start. This discussion, however has clarified some advantages that I wasn't aware of, AND clarified how we can improve the odds of the things activating in an accident.
I'm still going to wait to see the cost of that GPS enabled unit from Artex, though.....
And, by the way, from the SAR website:
Alaska Search and Rescue
The Alaska State Troopers, Dept. of Public Safety, have primary responsibility for civilian search and rescue in Alaska. Any search and rescue emergency should be reported to the nearest Trooper Detachment, Village Public Safety Officer, or to Trooper Dispatch in Anchorage (428-7200).
This is INFORMATION, not hearsay. It's not from "a neighbor", "someone I knew once", or.....as I said, the sergeant I spoke with at RCC Elmendorf yesterday had a LOT of this information wrong when I spoke to him.