Folks, I've been doing some research on how ELTs function, agonizing over the decision to purchase a new 406 ELT.

We've been having a "lively" discussion on the pros and cons of ELTs on another site. I just spoke on the phone with an engineer from one of the two big ELT manufacturers, and he explained the system to me. This is long, so get something to drink, but I think if you read on, you might get some good info:


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.....

I exercised my ELT two weeks ago returning from a Sioux Falls trip to see the kids. I landed on my "Minimum Maintenance, Travel at Your Own Risk" Road and drifted the right wheel onto the sod and gravel windrow left by the road maintainer. No pounding but instead it was a vibration up the gear leg that I could feel. My wife said, What's that flashing light ahead of me on the panel? It had triggered the ELT so I reached over and reset it. No one else flew over looking for me that afternoon, so I must be OK.

Thanks for the info on the ELT, I never knew how they triggered or how the whole system responds until now.

Excellent info. Thanks!

This points out the benefit of having a GPS-linked ELT. With a GPS-linked 406mhz ELT the SAR people have your exact coordinates as soon at the first burst to the geostationary satellite goes out. The phone is literally ringing at the coordination center with an exact lat/lon while you're unbuckling your harness and crawling out of the airplane.

But with a non-GPS-linked ELT the SAR folks need to wait until a pass or two of the low-orbit satellites have gone over before they have an accurate enough location to launch. The helicopter crew is sitting in the break room waiting for the next pass to happen while you're sitting out there on your own with your compound fracture watching your airplane burn. And those few hours can make a big difference - that single Otter in Ak went down at about 4pm, and by 7pm the weather had come down and everyone at the site was stuck there for the night.

An even worse scenario is having your airplane at the bottom of a lot of cold water while you're bobbing around in a life jacket and the helicopter crew are waiting for a fix that isn't coming.

My 406mhz ELT is not GPS-linked, but I invested in a $400 PLB which I hang on a string around my neck when I'm flying over water or particularily gnarly ground. It doesn't replace self-reliance or survival skills, but its a damned cheap insurance policy..

Good stuff, Mike.

I have been waiting for Pointer to get this unit TSO'ed:

http://www.skyhunter406.com/

Note in my post that Artex is about to release a ELT that has the capability of taking a GPS signal from a PORTABLE GPS. This unit is scheduled to hit the streets in the next couple of weeks. I am holding my breath, but I'm betting that the price will take my breath away nonetheless.....

I have also gotten information from a gent that ELT information goes direct to RCC (Rescue Coordination Center), whereas PLB data has to go to MCC (which for the US is in Washington, DC) where they assign the appropriate SAR asset to respond. In other words, it is POSSIBLE that a PLB would elicit a slightly or maybe significantly different rescue resource than an ELT would.

Still working to verify that bit of information.

MTV

Thats interesting and a little worrying..

I'm going to be purchasing the ACK-E04 which is a direct replacement for my current ACK. Price $585 Yay! .. not so fast. This unit is still hung up in the approval process. I called them and they are optimistic for a mid-September approval. They have been optimistic before. This seems like cheap insurance to me.

http://www.ackavionics.com/406%20Page.html

Like others, this unit needs to interface with a GPS to be more accurate. A Garmin GPS 18PC can be used for this and costs less than $100 if you don't have an on-board gps to couple to:

http://www.google.com/products/catalog? ... EgQ8wIwBQ#

Thanks for the article MTV- the info is useful.

What's to keep some dumb old farm boy from pickin up one of them thar EPIRB thingys, and, if the nature of the "event" warrants it, just slam that damned thing on a stump ground for good measure?

The Alaska Oteer float plane crash a few weeks ago and the Twin Commanche crash here in Montana a few months ago are examples. 406 ELT didn't work in either case.. Didn't matter in the Montana crash as it wasn't survivable but a bigger deal in Alaska. Want to be saved? Get a PLB or SPOT, especially the new Delorme SPOT unit where you can send custom texts from the unit.

In the Otter accident, the ELT wasn't adequately mounted. So, one of the lessons to come out of these accidents is make certain your ELT, whatever flavor it is, is adequately mounted to prevent it from dislodging in an accident.

I agree that a PLB is still a good adjunct to the ELT. But, what happens if you're alive but busted up so bad you can't activate the PLB, such as unconcious from a knock on the noggin......?

I think the points that this discussion highlighted for me is that the 406 system is a better system, but we aren't quite there yet in the "best" technology. A PLB is still a good unit to have along for a bunch of reasons. And, ANY ELT can be expected to work far better IF it's properly installed and the G-switch is properly exercised periodically.

Wannabe, an EPIRB is just a very expensive version of a PLB. Buy a PLB instead, most of which also have a GPS. The EPIRBs typically have an automatic activation device that turns them on when they get wet. Not really much value in aircraft.

MTV

Just to add confusion to this thread.

All aluminum bodied aircraft and fabric aircraft with "silver" in the covering process almost certainly will have to have their 406 ELT antenna mounted on the outside of the aircraft.

My question is if if the antenna is snapped off during an accident, what happens? Maule has an approval from (Airtex maybe) to mount the antenna inside the fuselage. Now this makes a lot more sense to me if you are able to do it. I seems something surrounded by a bunch of steel tubing has a much better chance of surviving than something external.

$0.02 worth.

TD

So, does anyone know anything about Emerging Lifesaving Technologies ELT406GPS? It appears to be a straightforward ELT with built in GPS, that Aircraft Spruce, and many others, sells for about $1,360.

mtv wrote:
I have also gotten information from a gent that ELT information goes direct to RCC (Rescue Coordination Center), whereas PLB data has to go to MCC (which for the US is in Washington, DC) where they assign the appropriate SAR asset to respond. In other words, it is POSSIBLE that a PLB would elicit a slightly or maybe significantly different rescue resource than an ELT would.

Still working to verify that bit of information.

MTV

It's my understanding that MCC will scan the registration information to see if it could be associated with an aircraft emergency, and if it is, it immediately goes to RCC. So there might be a delay, but if you have put the right data (N#, notes about typical use in an airplane, etc.) in your PLB registration information that goes to NOAA, the delay will be an extremely short one, and one might question the relative advantage of the AFRCC in the lower 48 knowing that you are tits up somewhere vs. the county sheriff or state EOC. Not much in my opinion. They'll call the RCC if they need the CAP anyhow :shrug:

In Alaska OTH, it might make a difference, but I doubt it because the four entities which typically take care of search and rescue no matter if it is aircraft-related or not - The Alaska Rescue Coordination Center which dispatches and controls CAP and ANG resources, the US Coast Guard, the Alaska State Troopers, and the National Park Service - all instantly call each other for help anyhow.

375,

I just called Aircraft Spruce about that ELT. I asked if it was approved for certified aircraft. His response was that it isn't APPROVED yet, for any aircraft. "Expecting approval sometime mid October".

Where have I heard that one before?

Once and Futr,

Yeah, that's what I figured. As long as a signal goes out as a distress, I seriously doubt ANYone is going to sit on it, and if it's in a remote part of the country, with the only access by air, I'm guessing that's who'll come looking. On the other hand, down here if you splat next to a road, the County Mounties might be your best bet anyway.

MTV

a 121.5 homer with a GPS 406 is what I run, well kinda

I have the standard issue 121.5 on the plane, then I have a epirb 406/121.5 with GPS with a built-in xeon strobe, in the rear of the plane, if I know it is going to be one of those days I will activate the epirb and aircraft's elt (remember reception vs altitude, also if your GPS is under a pile of rubble it wont be very effective.

The thing I like about the epirb is it is portable, floats and even has a tether. If the plane catches on fire I'm not going to try to wrestle a ELT out!



kinda like this one

I just installed an Artex ME406 ELT in my Maule MX-7-180 and discovered that the interface between the ELT and my panel mounted GX60 GPS/Comm is not yet FAA-approved. I'll have to do this later. I also carry a SPOT Messenger, which is more portable and can be used to send non-emergency messages without summoning SAR.