[Sam Buchanan]

The prelim report on the Ted Stevens crash in Alaska has been released. The following statement was part of the report:

"No emergency locator transmitter (ELT) signal was detected during the aerial search. (The accident airplane was equipped with an Artex ME406 ELT. Examination of the wreckage revealed that the ELT had separated from its mounting bracket during impact, and the antenna cable was found separated from the ELT.)"

The question about where to mount the ELT antenna has been hashed many times on this forum but I wonder if we have overlooked the importance of having a secure mount for the ELT that is likely to survive a crash. Mount integrity and keeping the coax intact is probably more important to transmitting a useful signal than where we mount the antenna.

 

[roee]

... Mount integrity and keeping the coax intact is probably more important to transmitting a useful signal than where we mount the antenna.

Both are important. For the ELT to do its job, a lot of things have to go right. Even with an ideal installation it's a game of probabilities. But installing it in such a way that any one of those aspects is significantly compromised from the get-go -- poor mounting integrity, vulnerable coax run, or poorly placed antenna -- will likely worsen the probabilities significantly.

 

[benamyava]

I will be installing a blade style antenna not an whip with the 406 unit I am waiting to receive.

I want to install the ELT in the aft fuselage with the antenna mounted to the bottom side of the fuselage. The canopy on my -8 slides all the way back to the vertical fin.

Thoughts? Suggestions?

 

[az_gila]

Interesting...

The prelim report on the Ted Stevens crash in Alaska has been released. The following statement was part of the report:

"No emergency locator transmitter (ELT) signal was detected during the aerial search. (The accident airplane was equipped with an Artex ME406 ELT. Examination of the wreckage revealed that the ELT had separated from its mounting bracket during impact, and the antenna cable was found separated from the ELT.)"

The question about where to mount the ELT antenna has been hashed many times on this forum but I wonder if we have overlooked the importance of having a secure mount for the ELT that is likely to survive a crash. Mount integrity and keeping the coax intact is probably more important to transmitting a useful signal than where we mount the antenna.

...and thanks for the link Sam.

I know that the older 121.5 ELTs will work with no antenna - a local mechanic did an accidental field test walking around with an ELT (he didn't know it was on) and got a CAP Cessna visiting our Airpark...

Because of the frequency characteristics and signal strengths of the 121.5 continous signal vs. the pulsed signal of the newer 406 ELT, I wonder if the new 406 ELTs will "hit" the satellite with no antenna attached.

Reading the above report, it looks like the answer may be no...

 

[ao.frog]

Bracket type?

I can't get the link to work, so does anyone know which type ELT-mountbracket was used?
For example a homemade one or the Vans ELT strobe/ELT mountbracket?

 

[pierre smith]

What we also need to consider...

...is that the -4, -6, -7 and -8 are stressed to 6 G's with an ultimate 9 G's before failure. This being the case, the ELT base has to be able to withstand 9 G's as well, as do our seat bottoms, which they will endure.

The problem comes when we mount the ELT without knowing how much forward impact it will stand, before it breaks away from its mounting. Perhaps an engineering graduate on here can offer some guidance as to how to determine how we could mount them substantially enough to be able to absorb most hard forward impacts.

Best,

 

[roee]

...is that the -4, -6, -7 and -8 are stressed to 6 G's with an ultimate 9 G's before failure. This being the case, the ELT base has to be able to withstand 9 G's as well, as do our seat bottoms, which they will endure.

The problem comes when we mount the ELT without knowing how much forward impact it will stand, before it breaks away from its mounting. Perhaps an engineering graduate on here can offer some guidance as to how to determine how we could mount them substantially enough to be able to absorb most hard forward impacts.

Best,

Actually, the airframe g ratings have little or nothing to do with it. Those simply tell you what flight loads the wings can withstand. The ELT installation needs to withstand the forces of any survivable crash, which may be far greater than that -- peaking in the neighborhood of 50 g, and potentially with strong longitudinal and vertical components.

It would be hard to know for certain that your installation could withstand this without actually testing it. However, you should be able to get a good installation by following some general guidelines from the manufacturers, AC 43.13, etc. Most important is to mount directly to a primary structure that is stiff and strong. Also, an aft location in the airframe is preferred, where impact loads will tend to be attenuated somewhat.

In my humble opinion, even the mounting plate that Van's sells is questionable in that regard. Seems pretty flimsy, and attaches to the j-stringers along the skin... On the -7 the best location I could come up with is on the aft deck just forward of the HS forward spar. That's a very strong intersection of the main longerons and a fairly beefy bulkhead. But this, again, is untested.

 

[Dave Cole]

Check the CG change

On the -7 the best location I could come up with is on the aft deck just forward of the HS forward spar. That's a very strong intersection of the main longerons and a fairly beefy bulkhead. But this, again, is untested.

Unfortunately, that location can have a significant effect on CG location in the -7, which tends to an aft CG anyway. For example, the ACK 406 MHz E-04 weighs 3.6 pounds (including the ELT, battery pack, and mounting tray). That's a lot of weight to put that far aft.

It would be a good idea to do some CG calcualtions before installing an ELT on the aft deck.

 

[terrye]

I couldn't find the FAA regulation, but the Canadian requirements in Part V, Airworthiness Manual Chapter 551 Section 104(f) ELT Installation states:
The ELT must be installed to withstand ultimate inertia forces of 10g upward, 22.5g downward, 45g forward and 7.5g sideward

So here's an easy way to make sure your mounting structure will withstand these loads. Multiply the ELT weight by these "G" loadings. Apply each of these forces to the bracket at the center of gravity of the ELT. This can be done with a spring scale. If unable to apply the load to the ELT itself, make up a dummy bracket to attach to the structure so the forces can be applied at the ELT CofG.

 

[N941WR]

I will be installing a blade style antenna not an whip with the 406 unit I am waiting to receive.

I want to install the ELT in the aft fuselage with the antenna mounted to the bottom side of the fuselage. The canopy on my -8 slides all the way back to the vertical fin.

Thoughts? Suggestions?

The only thought I have is that many people mount them aft of the baggage compartment bulkhead, which makes them unreachable in the event of an accident. Think twisted skins and a broken arm or hand, how are you going to reach it?

I mounted mine under the baggage compartment floor and used large knurled knobs to close the "door". The ELT tray is bolted to the side of a rib and does not rest on or touch the floor or bottom skin. I also made the portable antenna accessible. This adel clamp and cap screw hold the right flap arm cover in place. Some shrink tubing was put over the antenna to keep it from sliding out and the tip of it rests against the bulkhead so it won't slide forward in an accident.

Another location is to mount the ELT, point forward, right behind the passenger seat.

 

[roee]

Re: other installation considerations...

Unfortunately, that location can have a significant effect on CG location in the -7, which tends to an aft CG anyway. For example, the ACK 406 MHz E-04 weighs 3.6 pounds (including the ELT, battery pack, and mounting tray). That's a lot of weight to put that far aft. ... It would be a good idea to do some CG calcualtions before installing an ELT on the aft deck.

True, the effect on CG must be considered, and depends on other equipment you have installed in the airplane (e.g. heavy constant speed prop, or light weight fixed pitch?). FYI, there are other 406 MHz ELTs that are far lighter than that one. The compact units from Kannad are about half that weight.

The only thought I have is that many people mount them aft of the baggage compartment bulkhead, which makes them unreachable in the event of an accident. ...

Yep, that's another important consideration. Mounting the ELT on the aft deck allows easy access to it from outside the airplane, by simply removing or breaking the fiberglass empennage fairing.

 

[N941WR]

...Yep, that's another important consideration. Mounting the ELT on the aft deck allows easy access to it from outside the airplane, by simply removing or breaking the fiberglass empennage fairing.

Besides the aft CG issue you will create by putting your ELT on the aft deck, if you are injured, chances are you will not be able to break the fiberglass (or reach it if the tail is sticking straight up and you have a broken leg/ankle). You will have to keep a screwdriver handy to remove that fairing, which is another tool that may not be available.

In addition to all that, you will have to find a place to mount the antenna. Under the empennage fairing seems like a good location. This will require you to run the cable forward and then back to the antenna. If you want an external ELT antenna, you will have to run that cable through three bulkheads to get it far enough forward to keep it from hitting the VS in flight.

PS. Heck, even if you are not injured, you probably can't break that fiberglass empennage fairing. That FG is tough stuff!

 

[Ron Lee]

Opinion follows

A 121.5 Mhz ELT and possibly 406 MHz units (unknown) are mandated dead weight.

I have zero confidence that they will work when needed. I carry a 406 MHz (internal) GPS PLB that offers a far better notification to SAR assets should I be alive. Actually if I am going down in a controlled situation, ideally it would be activated while airborne.

If I am dead, no one cares anyway and I have a will for that contingency.

 

[Sam Buchanan]

If I am dead, no one cares anyway and I have a will for that contingency.

Most likely the SAR folks will want the assistance of an ELT (APRS is my best bet) to conclude the search for your plane and recovery of your corpse as quickly (inexpensively) and at as low risk to their personnel as possible.

 

[roee]

Besides the aft CG issue you will create by putting your ELT on the aft deck, if you are injured, chances are you will not be able to break the fiberglass (or reach it if the tail is sticking straight up and you have a broken leg/ankle). You will have to keep a screwdriver handy to remove that fairing, which is another tool that may not be available.

In addition to all that, you will have to find a place to mount the antenna. Under the empennage fairing seems like a good location. This will require you to run the cable forward and then back to the antenna. If you want an external ELT antenna, you will have to run that cable through three bulkheads to get it far enough forward to keep it from hitting the VS in flight.

PS. Heck, even if you are not injured, you probably can't break that fiberglass empennage fairing. That FG is tough stuff!

Bill, I think the main reason you'd want to be able to physically get to the ELT unit itself is in a scenario where you choose to hike away from the wreck and take the ELT with you to use as a portable. If you're so injured that you physically can't get out of the airplane, then you're not going anywhere anyhow, and so physically getting at the ELT is moot.

The fiberglass fairing is easy to break away with any prying tool, stick, rock, or even bare hands. It is not that tough at all. We're talking about a scenario where the airplane is wrecked... gently unscrewing the fasteners is not what I had in mind.

The external antenna goes on the top of the fuselage just aft of the F-708 bulkhead. That's about 18 inches forward of the base of the vertical stabilizer. With the newer 15 inch antennas there is no possibility of contact with the VS. With the older 24 inch antennas there is still practically no possibility of contact unless you bend over the antenna 90 degrees at its base.

The coax only has to pass through one bulkhead, the F-709, which has a 4 inch diameter lightening hole just forward of the ELT unit.

 

[az_gila]

You may have a will...

.....
If I am dead, no one cares anyway and I have a will for that contingency.

...but your family/loved ones will be in limbo until you are found, or quite a length of time has passed.

I know of one case where a missing plane (and fatality) did cause family troubles...

 

[N941WR]

Bill, I think the main reason you'd want to be able to physically get to the ELT unit itself is in a scenario where you choose to hike away from the wreck and take the ELT with you to use as a portable. If you're so injured that you physically can't get out of the airplane, then you're not going anywhere anyhow, and so physically getting at the ELT is moot.

Exactly what I had in mind but with the hard core backpacking I have done, you would be surprised at how far someone can go with a broken arm or leg. However, if I were injured and the plane damaged, I would still dig out my ELT and put on the external antenna to make sure it was sending a signal, even if I were to stay with the plane.

The fiberglass fairing is easy to break away with any prying tool, stick, rock, or even bare hands. It is not that tough at all. We're talking about a scenario where the airplane is wrecked... gently unscrewing the fasteners is not what I had in mind.

That's what I understood but make up a section of fiberglass as thick as the fairing and then try to break it. You will find it isn't that easy, even with a rock, prying tool, or stick.

The external antenna goes on the top of the fuselage just aft of the F-708 bulkhead. That's about 18 inches forward of the base of the vertical stabilizer. With the newer 15 inch antennas there is no possibility of contact with the VS. With the older 24 inch antennas there is still practically no possibility of contact unless you bend over the antenna 90 degrees at its base.

The coax only has to pass through one bulkhead, the F-709, which has a 4 inch diameter lightening hole just forward of the ELT unit.

IMHO, it is better to keep the center of of mass in the center of the plane to make it handle better. Putting the ELT right behind a passenger seat is probably the best option and makes it easy to access, no bulkhead to remove, no fiberglass to brake, etc. and it really doesn't take up much room in the baggage compartment or get in the way of luggage.

Better yet, if you are incapacitated, it will be easy for your passenger to locate and hopefully you have briefed them of its existence, location, and use prior to flight. (I don?t always do this, as most of the time I am flying with my wife or other pilots.)

One other thought, before you put that concentrated weight back there, read up on Art Scholl?s accident in his Pitts S2 during the filming of Top Gun. Somewhere I read that the concentrated weight of the camera mounted on the tail made it impossible to recover from an inverted flat spin, even though the aircraft was within W&B. Not that you will do inverted flat spins in your RV, but it is something to think about.

 

[roee]

... if I were injured and the plane damaged, I would still dig out my ELT and put on the external antenna to make sure it was sending a signal, even if I were to stay with the plane.

Bill, if you're staying with the airplane and the ELT/coax/antenna installation has not been compromised, then you're likely to get a better transmission with the installed antenna which has a good ground plane. That of course assumes that you've installed the antenna in a suitable location, per manufacturer's guidelines. If that's not the case, or if the installation has been damaged or the airplane is up side down, then indeed you may be better off going to the portable antenna, even if you stay with the plane.

... That's what I understood but make up a section of fiberglass as thick as the fairing and then try to break it. You will find it isn't that easy, even with a rock, prying tool, or stick.

I'd bet money I could tear that fairing right off the airplane with one hand. If you wish, I'd be happy to demonstrate on YOUR airplane

... Somewhere I read that the concentrated weight of the camera mounted on the tail made it impossible to recover from an inverted flat spin, even though the aircraft was within W&B. ...

Understand the issue with concentrated mass at the extremities, but keep this in perspective. How much do you think a 1980's film camera weighed? A modern ELT installation weighs only about 2 lb. I'd have no major concerns with adding 2 lb near the tail of my 7A. How much does the tail wheel installation weigh on the non-A model? I'll bet it's no less than 2 lb, and it's located even further aft. Clearly that hasn't been a problem.

... Putting the ELT right behind a passenger seat is probably the best option and makes it easy to access ...

Installing the ELT there as you suggest could be ok, but all the same issues still need to be considered: sturdy mounting, correct orientation (parallel to longitudinal axis), suitable antenna location, coax run that is not likely to be severed in a crash, etc. And then with an installation in the baggage compartment there are additional issues that must be carefully considered. That level of accessibility is a double-edged sword. The ELT is in an area that is routinely accessed by pilot and passengers, objects (baggage, etc.) are routinely taken in and out, and when baggage is in it may not always be quite so secured so it can't shift around. The location is not inherently protected, so you should have some means to ensure that the ELT doesn't get hit by these other objects, which could potentially damage it or its wiring harness, or accidentally activate it with even a casual bump. I'm sure you've considered all this and taken precautions, but I thought it would be worth mentioning.

 

[Ron Lee]

The portable 406 MHz PLBs (with integral GPS) are selling for around $200 USD (ACR Terrafix) or $250 USD (Fastfind 210).

 

[N941WR]

Roee,

Sounds like you have thought about this a good bit and have made up your mind to place the ELT that far aft. Let us know how it works out.

When contemplating a modification or installation that is different from “standard” (if there is such a thing as “standard” on our homebuilts), how many RV's are flying with idea X vs. the standard or generally accepted practice? That usually brought me around to dropping my idea.

Something else for you to think about, you mentioned the tailwheel weight. Just remember, the main gear on the A models are aft of the CG and depending on your engine/prop combination, they tend to suffer an aft CG issue when compared to the TW models. Something to think, about should you elect to put even two pounds that far aft.

Ron,

I tend to agree with you. The ELT is only there to make the CAP happy. Some time ago one of our VAF members who is also an SAR specialist mentioned that in all the accidents he worked, when the ELT went off it was a "recovery" effort, not a "rescue". His comments were very telling.

 

[ACR406]

If you want to make sure the 406 MHz ELT is installed correctly and the ELT is transmitting to the satellites use www.406Test.com service from ACR. You get a confirmation SMS text message when you perform a self test of an installed 406 ELT seconds after you perform the test. This way you know (1) that the beacon is transmitting with enough power, (2) the antenna is working and properly installed and (3) that the satellites picked up the signal.

We just launched this website and its quick and easy to use. Plus it doesn't require any expensive ELT Testing equipment. If you have any questions let me know.
Mikele from ACR Electronics.

 

[ChiefPilot]

A 121.5 Mhz ELT and possibly 406 MHz units (unknown) are mandated dead weight.

I have zero confidence that they will work when needed. I carry a 406 MHz (internal) GPS PLB that offers a far better notification to SAR assets should I be alive. Actually if I am going down in a controlled situation, ideally it would be activated while airborne.

If I am dead, no one cares anyway and I have a will for that contingency.

I couldn't agree with you more. Numerous ELT failures have shown that they aren't a surefire bet, but the cost + weight penalties sure are.

The only reason my plane has an ELT is because I have to have one. I don't really care much how it is mounted so long as it doesn't interfere with anything else. That, and not crash survivability, was the primary factor in how I mounted mine.

 

[roee]

Let's stay on topic...

Every time an ELT-related thread comes up, no matter what the specific question or topic, a number of people insist on interjecting what amounts to nothing but blanket statements that ELT's are useless dead weight, etc., etc. The opinion has been heard and noted. The general efficacy of ELT's is a fine topic for debate, but it doesn't belong in endless repetition in every single ELT-related thread. That serves nothing but to dilute the discussion on the original topic of the thread. For those who insist on debating the general ELT efficacy question, please do so in a thread dedicated to that question, preferably under the "never ending debate" section next to the primer wars et al. Thank you.