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Emerging Lifesaving Technologies ELT install

Why would you want one without a 121.5 transmitter? So those nasty CAP people can't locate you?
 
"Upon receiving the initial notification of a 406 ELT activation, the Cospas-Sarsat Low Earth Orbiting (LEO) satellites utilize Doppler shift to locate a specific beacon. The satellites pass overhead and chart their position as they pass over the beacon. Cospas reports that a 1-3 nm (2-5 km) accuracy on average is determined this way. This makes the search area approximately 25 sq. nm (65 sq. km) or about 3700 acres large.
The time required to listen to the short message format of a non-gps enabled 406 ELT and make this calculation using the initial detection of the orbiting satellites is about 45 minutes with a maximum of 90 minutes.
Subsequent satellite passes every 60 minutes will refine the position, with a maximum time of 90 minutes for each pass.
A 121.5 homing beacon is then used to narrow the search to within ¼ mile.
406 ELTs equipped with GPS send long message formats that include the latitude and longitude within 4 sec (as in degrees > minutes > seconds) of the location. This gives you an accurate position of better than 300 feet.
GPS position that is sent on the first burst or initial alert provides a near instantaneous accurate fix using the US maintained SARSAT geostationary satellites which monitor nearly the entire globe at any given moment.
Each 406 ELT sends a specific ID combined with registration data and point of contact information. This allows for a potential near real-time immediate launch of search and rescue (SAR) assets to your exact location. There is no need to wait for the multiple passes of LEO satellites required to narrow your position to a manageable search area for SAR.
Emerging Lifesaving Technologies 406 ELT with GPS can be activated while still in the air and send accurate positional data. If for some reason the aircraft was too damaged to send information to SAR after the incident, this could mean the difference between rescue and recovery.
Although the internal GPS updates the unit every second, Cospas Sarsat rules allow the data burst to be only updated every five (5) minutes. This is prevents a new alarm going off at the MCC (mission control centers) at every burst. "

At best 121.5 is redundant.

In reality, in most cases it's just useless.

As Bob T. says.........opinion( I have no opinion on this particular ELT)
 
And nothing can possibly go wrong....go wrong....go wrong....go wrong....go wrong....go wrong....:-?

It's practical(barely) for a satellite-based platform (and ground based computers) to employ doppler and curve matching to DF a signal that only occurs every 50 seconds, but not a search aircraft. Hence, all of the search aircraft out there have 121.5 DF equipment, and even we can use the wing-null method to DF our buds..(works well on cubs)....a little redundancy in the real world is a useful thing to have...

(signed) The Department Of Redundancy Department


everyone know how to do the wing-null method of DF?
 
Fobjob,

For a redundant 121.5 beacon to be theoretically effective the ELT must continue pinging while searchers are arriving into the area. Think about that. For a 406 ELT to trigger a search effort requires the beacon to go active and be identified (you did the required NOAA registration, right?) and a telephone investigation, which is always the first response to a beacon. The rescuers are not going to fire up a helicopter until the event has been validated. In Alaska that takes between 30-60 minutes by the time the RCC contacts the people on your call list, checks flight plans, looks at tracker logs, etc and decides there's a real potential that there's an aircraft emergency. Then they launch. So let's assume the beacon is still active. By that time your location solution has been refined and the rescue guys are going to fly right to you with a reported accuracy of something in the scope of <25 meters. That report from a couple of helicopter captains at RCC who've been flying these missions for years. Interesting that these guys employ ACK ELTs with external GPS interface themselves in their own planes. Having a location report signal for a plane that may burn or sink is a good reason. Leave a path to the recovery site. That's what GPS enabling is good for. Whether the beacon survives to ping away or dies after 2-3 minutes there's little evidence that the 121.5 component of a beacon does anything important. I wouldn't hesitate to use a beacon that didn't have a 121.5 co-broadcast. Nobody would miss it.

The CAP running around an airport with a 121.5 homing device is a funny thing to watch. The RCC will have called me to ask if there's an emergency (406 registered signal) WAY before any CAP guy could locate a 121.5 beacon at Lake Hood. That alone demonstrates the relative uselessness of 121.5. Yet guys still elect to fly into the wild with them. I don't care which 406 any guys choose to buy or why. All TSOd 406 ELTs are far, far superior to any 121.5 ELT that was ever produced. Just get one.

SB
 
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fobjob said:
And nothing can possibly go wrong....go wrong....go wrong....go wrong....go wrong....go wrong....:-?

It's practical(barely) for a satellite-based platform (and ground based computers) to employ doppler and curve matching to DF a signal that only occurs every 50 seconds, but not a search aircraft. Hence, all of the search aircraft out there have 121.5 DF equipment, and even we can use the wing-null method to DF our buds..(works well on cubs)....a little redundancy in the real world is a useful thing to have...

(signed) The Department Of Redundancy Department


everyone know how to do the wing-null method of DF?
Click to expand...

I agree that having a 121.5 signal to track is a bonus. I have a 121.5 DF radio permanently installed in my Cessna. Though the 406 is superior in all ways an actual search is still a search and having a 121.5 signal to track is one more helpful tool.
 
The question is not whether to get a 406 ELT, but: do things always work the way they should in the real world....as much as I like the "no sparrow shall fall" ambitions of the new SARSAT philosophy, it has flaws.(some of which you described)..I would have a 406 ELT(WITH a 121.5 xmitter) AND a PLB, AND a sat phone AND a SPOT before I flew over British Columbia, for example....I'm installing ADS-B (in) and APRS and a strobe power supply at the moment...the 406 will have to wait till later this summer....after spending 20k on rebuilt wings (while my knees and ankle went to junk) over the last two years, I'm kinda wore out....

ps...the people you see CF ing at the airport are trainees, every wing has two or three real experts in Df ing from the air that show up on actual searches....just so you know...
 
Whether a 406 beacon remains viable and active or a GPS enabled 406 sent a couple of transmissions out prior to being destroyed, a 406 beacon action is not a search. It's a rescue and recovery. You can tighten your survival potential by employing a good tracker. 121.5 is past it's prime. It has been for decades. We have much better equipment available to us. There's little reason to cling to the antiquated 121.5 habit. Leave it for the historians. I'm not a fan of government in my life but since ELTs are required and public assets are used to respond to aircraft accidents, I firmly believe that 121.5 beacons should be outlawed and 406 beacons should be required equipment in all aircraft.
 
Thread drift boys... :lol: I'm just looking to see if anyone here has installed one of these babies so I can get some info on the specifics before I wade into it.
 
sb, you and I are arguing over different subjects. Gotta go install stuff now.
 
I too believe the 406 MHz ELTs are vastly superior to previous versions. That said, having searched for ELTs on CAP ground teams, I think the 121.5 homing beacon is a good idea. Locating the plane in the last few hundred yards can be in snowy mountainous terrain can be very difficult. Also, the survivors may have removed the ELT and taken it with them, so the plane itself may not be an effective visual marker.

The new ELTs transmit the 121.5 signal at relatively low power compared to the 406 signal. - it's just intended for close-in location. While redundancy always requires design compromises, there's not much downside to the 121.5 homing beacon other than a little shorter battery life. Given that survivability goes down exponentially with time, I'd rather be found in the first day than save battery for the third day.

Update: Some posts crossed in the night. To clarify, the 406 ELTs have the option to implement a 121.5 MHz homing beacon, and most do. The E.L.T. ELT does not. Most of this discussion is about whether the "redundant" homing beacon is worth it.
 
Pundy,

The hard part of any ELT installation is the structural requirement. Max deflection of the installed ELT can't exceed 1/10th of an inch with 100# of applied force in the most flexible direction. That applies to all ELT installations and there are lots out there that don't meet the standard. Have fun and give us a pirep when you're finished, please.

SB
 
I installed an emerging lifesaving tech 406 ELT's 2 years ago.....had some issues with a fabric aircraft that they had not forseen. I had to ground the unit to the airframe and all was right with the world. Larry
 
So Larry, did you try to create their 285 square inch "ground plane" that they prescribe? Or did you just ground it to the airframe and leave it at that? Was yours an install in a Cub?
 
Install was on Citabria....ground plane small, like 6X6, so ground to airframe did the trick. This was their suggestion as I was out of ideas.....but it worked. Larry
 
Ground plane or counterpoise is what the antenna works against. The antenna has voltage and current on it that has to be "absorbed" someplace (not technically correct but works for a visualization). A quarter wave vertical needs a groundplane 360* around it to function omnidirectionally. Think about broadcast (AM type) towers, they have over 200 buried radials spaced in a spoke pattern radiating from the base of the antenna. If they had only one 1/4 wave groundplane radial they would radiate much more signal in the direction the radial is aiming. This is tantamount to mounting an antenna on say a spar where the signal would be strongest sideways to the aircraft. Things to think about during an install.
 
SB said


"I firmly believe that 121.5 beacons should be outlawed and 406 beacons should be required equipment in all aircraft. "

Ditto
 
I would have done the 406 ELT last year, but it needs a new(additional) plywood mounting platform, and a new antenna mount on the aft fuselage, because I will not use the hatch cover again, and I don't want to put it on top of the wing for crash vulnerability reasons. Acceptable losses in the coax run to the antenna also limit you to 9 feet, and my personal limit is 5 feet. So, I was going to fabricate a .032 mount to bridge the fuselage aft of the access hatch. That's a lot of PITA fabrication that I haven't been willing to deal with as yet. (I might wind up settling for the hatch cover, but the idea makes me cringe, as it is a minimal counterpoise) It still has to operate and radiate when it's on it's back, so there's no point in doing a quickie half-vast job of it....
 
fobjob said:
I would have done the 406 ELT last year, but it needs a new(additional) plywood mounting platform, and a new antenna mount on the aft fuselage, because I will not use the hatch cover again, and I don't want to put it on top of the wing for crash vulnerability reasons. Acceptable losses in the coax run to the antenna also limit you to 9 feet, and my personal limit is 5 feet. So, I was going to fabricate a .032 mount to bridge the fuselage aft of the access hatch. That's a lot of PITA fabrication that I haven't been willing to deal with as yet. (I might wind up settling for the hatch cover, but the idea makes me cringe, as it is a minimal counterpoise) It still has to operate and radiate when it's on it's back, so there's no point in doing a quickie half-vast job of it....
Click to expand...

Fob,

thats what precipitated my question on the other thread about mounting the ELT antenna internally. That certainly seems the best for survivability, but only if the fabric and coatings don't seriously degrade the outgoing signal.

i installed an ACK 406 in my 170. It malfunctioned (bad switch....covered under warranty) and transmitted. I removed it from its bracket, disconnected it from its external antenna, and placed in the center of the aft cabin....about where the rear seat would normally be.

The faulty switch activated again, and RCC received the signal....with NO antenna attached to the unit, and with the unit inside a metal fuselage. And, the ELT was still transmitting the last known position from the GPS, which was also disconnected.

Based on that experience, I suspect that an antenna mounted internally in the aft fuselage would probably work fine, and be a lot less susceptible to crash damage.

And by the way, the 406 signal goes out at a full five watts, compared to the milliwatt signal that the old 121.5 units transmitted. Since the 406 is a very short burst signal, as opposed to the continuous 121.5 signal, it can be sent at much higher power without compromising battery life.

FWIW

MTV
 
Mike,

I believe you're misinterpreting the other thread. The GPS receiver in that unit is internal and does not require an external antenna. The ELT transmitter does use a BNC connector to a cable to an external antenna. Or you can connect the supplied short whip antenna and take the unit mobile. In any case it requires an antenna.
 
Mike, an internally mounted antenna requires a lot of testing, and I consider it to be bad practice in general, but the crash vulnerability of an external one leads one to search for a good compromise....I intended to mount one (externally) just forward of the vertical stabilizer,(for ground clearance while inverted) but that requires additional structure, with metal running just under the surface of the fabric, and a transition through the fabric that an FAA person might have to be convinced of...an antenna mounted to the access hatch has a big problem with adequately anchoring the coax against crash loads. The existing (dual band) 406-121 antennas I see seem to be compromises that probably need an adequate ground plane more than the average single-band antennas. Remember that the 406 burst has to reach the GPS satellites 5000 miles up there...they were going to put the translators on synchronous satellites, but 23,000 miles proved to be just too much path loss...
 
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sierra bravo said:
Mike,

I believe you're misinterpreting the other thread. The GPS receiver in that unit is internal and does not require an external antenna. The ELT transmitter does use a BNC connector to a cable to an external antenna. Or you can connect the supplied short whip antenna and take the unit mobile. In any case it requires an antenna.
Click to expand...

Stewart,

read my post, please. My point was that at least one 406 ELT was able to alert RCC of its location (at shutdown) EVEN THOUGH the ELT was not connected to ANY antenna. That was the point of my post. I SUSPECT, based on that experience, that a 406 ELT with an antenna mounted INSIDE the aircraft structure MAY work just fine.

I would not consider mounting an ELT antenna inside a metal fuselage, but I'm thinking that mounting an ELT antenna (NOT a GPS antenna, Stewart) inside a fabric covered airplane may be a good plan. That might provide some level of protection for the antenna in an accident.

MTV
 
We put both the comm and 406 antennae inside the fuselage on our Rans build. Works fine. I asked my AK Airlines buddy who is an avionics maintenance guy about it first, he said "Boeing is doing it on their -37's so it should be good enough for you."
 
"In Theory, theory and practice are the same...in Practice, they aren't"....

Antenna theory, especially...in certified aircraft, you have to conform to what is referred to as "Generally Accepted Practices" in order to get an easy approval to something you are doing ...with ELT antennas, that generally implies:
Use an externally mounted antenna, (the one provided!!)fastened to a structural ground plane, with coax securely fastened(adel clamps, usually) at both ends and every six inches along the length...mounted as high as possible, and clear of other structure....the reasons are that every conducting piece of structure within several wavelengths of the antenna become a parasitic element of the antenna and affect it's radiation pattern and efficiency.(drastically!) That means that putting an antenna inside a (truss type) metal structure will result in unpredictable results* ...that means you would have to measure the antenna's radiant efficiency and directionality....anyone have the equipment to do that to the satisfaction of the FAA?? They don't have guidelines for that, so good luck. And, bear in mind, that it still has to radiate upwards, when the aircraft is on it's back, as well....
Airliners sometimes use slot antennas, which use metal adjacent to a slot in the skin to radiate. (which is structurally problematic in a monocot airframe)You could cut a slot antenna in a sheet of aluminum and mount it to the fabric(or under the fabric) on the top of the rear deck, BUT the fabric near the slot area AND the area around it would have to be non-conducting and non-resistive. No metallic UV protection...Also, it wouldn't radiate upwards too well when it was on it's back. AND it would still interact with nearby structure....which could result in directional lobes that could prevent contact with a satellite....unpredictably...
After a lot of cogitation, it seems to me that using the provided antenna, fastened to an aluminum deck just forward (40 inches or so) of the vertical stabilizer, and canted(to the side) to the max allowable 30 degrees, would be the best compromise to all of the above problems.

* 'unpredictable results' means multiple lobes and notches in the directionality. If the satellite happens to be in a lobe, no problem...if it's in a notch, tough kanuckies....
 
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fobjob said:
"In Theory, theory and practice are the same...in Practice, they aren't"...
After a lot of cogitation, it seems to me that using the provided antenna, fastened to an aluminum deck just forward (40 inches or so) of the vertical stabilizer, and canted to the max allowable 30 degrees, would be the best compromise to all of the above problems.
Click to expand...

Perhaps....Until you wind up on your back. That is the conundrum with these aircraft......and a very likely outcome of an "oops". A "properly mounted" (according to the "normally accepted guidelines") antenna that is broken off and upside down may or may not provide any better radiating properties than an intact internally mounted antenna.

i agree that it would be nice to have this configuration tested, though.

But, while probably not a sound test, the fact that my ACK ELT lying in the passenger area of a metal airplane, not attached to ANY antenna at all still transmitted a valid signal via the satellite to RCC certainly suggests to me that internally mounted in a fabric plane, WITH an intact antenna MAY be a suitable program.

Did I use enough weasel words on that? :lol: :roll:

And when this occurred, I spoke to the nice Major at RCC McDill and specifically verified that they were receiving a strong signal, AND it was clear enough for him to decode and generate GPS coordinates, from the last GPS location before I disconnected the ELT from the aircraft....the location he read to me was indeed within a few meters of where the airplane was parked.

The only explanation I can offer is that, as I noted before, the 406 signal is transmitted at very high power, compared to the old 121.5 beacons. Five watts is a lot of power.

I haven't decided where the antenna's going on my Cub yet, though. :oops: :roll:

MTV
 
mvivion said:
Perhaps....Until you wind up on your back. That is the conundrum with these aircraft......and a very likely outcome of an "oops". A "properly mounted" (according to the "normally accepted guidelines") antenna that is broken off and upside down may or may not provide any better radiating properties than an intact internally mounted antenna. MTV/QUOTE.

Mike, my reasoning is that the antenna on the ACK is flexible and roughly 23inches long...mounting it where I stated would protect it from the ground and get it sufficiently clear of structure and ground (remember the side cant angle) to survive the flip and still have a view of the sky....unless you packed up a wing as well, and it was now exactly under the structure...again, inside the fuse is not predicable, not certifiable, not testable....However, for the purposes of Bovine Scatology, I'm more than willing to discuss it! My favorite approach would be a balanced dipole, located along the longitudinal axis of the aircraft, above the truss, below the top deck, as clear of structure as possible. Hope that you have wood stringers, though....if you don't, that's not necessarily a deal killer. Make sure the ends of the dipole (especially) are as clear of metal structure as possible. The center of the dipole could be close to the stringer, but make the end as far away as possible. The stringer has now become part of your antenna...not necessarily a good part... I am NOT recommending this...
Click to expand...
 
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