Help identifying ELT antenna

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bkspero

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bkspero
Went to the plane today and found what I think is my ELT antenna bent horizontal and broken to the point that it was barely hanging on to the stub (it's an old 121.5 ELT).

I could use some help identifying its replacement. The antenna is a piece of 1/16th inch stainless steel wire that goes into a plastic collar that projects through a ca. 1/2 inch diameter hole in the fuselage. Mounted below the antenna against the inside of the skin is a sheetmetal box (see the attached photo). There are two screws through the fuselage skin from the outside that seem to hold the box and antenna in place. One screw is about 1 inch ahead of the antenna and the other about 1 inch behind the antenna. What appears to be coax cable runs from the box to the tail of the plane where the ELT is located.

I can't find any antennas that look like identical replacements for mine, and would appreciate it if someone could identify it for me.

Thanks, Barry.
 

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bnt83 said:
Why do you have to have the exact same one?

Looks to me like you have AmeriKing AK450 ELT...


http://www.aircraftspruce.com/pages/av/elts_rant/ak450eltant.php
Click to expand...

Mine doesn't widen near the base for several inches. The plastic collar from which my antenna extends is only anout 3/16 of an inch in diameter and about 1/8 inch high. Just enough to barely protrude through the skin. I don't see how it can be separated from the box below.

Was too late yesterday when I found it to have the shop look a it. I'll have the shop look at it today. It would be great if I was missing something and the fix is a $40 part installable from outsde.

Thamks for the input.
 
1RTK1 said:
Looks like a Grumman, try Ken Blackman or Fletchair
Click to expand...

It is a Tiger. But the antenna install is different from what is described in the maintenance manual. The manual describes it as being underneath and protruding through the dorsal fin. Mine is off to the side.

Still, I should and will call them today. Thanks
 
1RTK1 said:
Looks like a Grumman, try Ken Blackman or Fletchair
Click to expand...

It is a Tiger. But the antenna install is different from what is described in the maintenance manual. The manual describes it as being underneath and protruding through the dorsal fin. Mine is off to the side.

Still, I should and will call them today. Thanks
 
1RTK1 said:
Looks like a Grumman, try Ken Blackman or Fletchair
Click to expand...


It is a Tiger. But the antenna install is different from what is described in the maintenance manual. The manual describes it as being underneath and protruding through the dorsal fin. Mine is off to the side.

Still, I should and will call them today. Thanks
 
Is the fuselage skin too thick to mount the antenna directly on it, hence the need for a sheet metal bracket and a plastic grommet?

 
Skin is normal thickness there. No honeycomb. I looked at it again this AM and was wrong about my recollection of a 1/2 inch hole. The antenna hole is only about 1/4 inch. The plastic collar that extends thru that hole is about 3/16 in dia and 1/8 inch tall, and the mast was 1/16 dia and about a ft long. All this mounts into top of box below skin and that box is held (sealed) against the underside of the skin by 2 screws thru the skin and into the box from above. No apparent way to disconnect antenna mast from box under the skin.

Shop not familiar with model.
 
bkspero said:
Skin is normal thickness there. No honeycomb. I looked at it again this AM and was wrong about my recollection of a 1/2 inch hole. The antenna hole is only about 1/4 inch. The plastic collar that extends thru that hole is about 3/16 in dia and 1/8 inch tall, and the mast was 1/16 dia and about a ft long. All this mounts into top of box below skin and that box is held (sealed) against the underside of the skin by 2 screws thru the skin and into the box from above. No apparent way to disconnect antenna mast from box under the skin.

Shop not familiar with model.
Click to expand...

You could mount a new $38 antenna directly to the skin or a variant of this:






This would make it possible to R&R the antenna without having to climb back into the tailcone. But you will need string to drag the antenna/plate assembly up to the hole.
 
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I don't think you are going to find another antenna like the one you have. I looked all over the net and couldn't find anything which leads me to believe that was the original from when the airplane was built AND not replaced when the AK450 ELT was installed (replacing an even older ELT).

Which makes me question if that old antenna is even appropriate for the ELT you have.
 
Can you find in you aircraft records what ELT was originally installed? That might lead you to a system description which might have an antenna part #.

Aircraft logbook or the equipment list might even have the antenna part #, elt part # or something helpful.
 
bnt83 said:
Can you find in you aircraft records what ELT was originally installed? That might lead you to a system description which might have an antenna part #.

Aircraft logbook or the equipment list might even have the antenna part #, elt part # or something helpful.
Click to expand...

First, at the time an ELT was an option on Tigers and if it was installed at the factory the antenna would have been centered left/right on the fuselage and projecting through a hole in the dorsal fin leading to the vertical stabilizer. That my antenna is mounted off center alongside the dorsal fin indicates that it was an aftermarket installation. This is corroborated by an logbook entry about 5 months after issuance of its Airworthiness Certificate (in 1976) that the plane was being flown without an ELT installed.

I see two log entries that relate to installation of what appears to be an ELT and nothing identifying the antenna. Six months after the airworthiness certificate was issued the owner had the original Narco Nav/Com replaced with a stack of Edo-Aire comm and nav radios. That list included the model number and type of device for every entry on the list except one. That one was identified as an ELT-551 (no device type listed). Google doesn't show up anything relevant in a search of that model number, but I still suspect that it was the 1st ELT in the airplane. There was a radio antenna on the list (for the 2nd Com radio) and an ADF antenna for the ADF, but no listing for an ELT antenna.

Every annual thereafter had a reference to either changing the ELT battery, or the date when the ELT battery needed to be changed. So there was an ELT in the airplane from then on.

Nineteen years later in 2005 there is an entry where the unspecified existing ELT was replaced with an Ameri-King 450 ELT to comply with TSO-C91a and DO-160c requirements. There was no mention of anything relating to the ELT antenna.

Not much to go on. Best guess would be that the antenna in the plane was the original one that came with an ELT from Edo-Aire model ELT-551 (would be great if someone could confirm or refute the existence of such a unit in the past). And the antenna was not changed when the AK-450 was installed in 2005.

One more thing. Every annual since I purchased the plane in 2012 we have done an ELT check in the airplane using the panel switch to activate and then reset the ELT. We have always gotten a strong signal broadcast from the AK-450 ELT via the now broken antenna.
 
To be legal, the antenna should be matched to the ELT. That old antenna probably doesn't match up well at all with the AK-450. Whoever installed the ELT was too lazy to install the antenna that came with it.

AK-450s are horrible ELTs. Their G-switch fails the annual tests way too often and the factory won't play ball. I wouldn't spend any money on it whatever. For a 121.5 I'd buy an ACK E-01 (if you can find one) since it uses Duracell D-cells and works well and comes with an antenna. Other than that, a 406 would be the best bet but you'll spend money doing it.
 
Dan Thomas said:
To be legal, the antenna should be matched to the ELT. That old antenna probably doesn't match up well at all with the AK-450. Whoever installed the ELT was too lazy to install the antenna that came with it.

AK-450s are horrible ELTs. Their G-switch fails the annual tests way too often and the factory won't play ball. I wouldn't spend any money on it whatever. For a 121.5 I'd buy an ACK E-01 (if you can find one) since it uses Duracell D-cells and works well and comes with an antenna. Other than that, a 406 would be the best bet but you'll spend money doing it.
Click to expand...

I think the AK450s aren't very good either. The one I see every year has yet to fail the G switch tho. If you bang them against something, even your hand, they won't reset. If you firmly grasp them with both hands and just swiftly move it and suddenly stop they seem to work fine.
 
Mine has passed its annual test for the last 10 years. Found out earlier today that the old antenna disqualified the install for the TSO and decided that I had to change to the AK antenna and keep the ELT. Will ask for a quote usthing the install method suggested by Brian so replacement is easier. If its more than about 3 hrs of labor, then I may switch to a 406.

Thanks all for the help.
 
bkspero said:
Mine has passed its annual test for the last 10 years. Found out earlier today that the old antenna disqualified the install for the TSO and decided that I had to change to the AK antenna and keep the ELT. Will ask for a quote usthing the install method suggested by Brian so replacement is easier. If its more than about 3 hrs of labor, then I may switch to a 406.

Thanks all for the help.
Click to expand...
Even if you keep your old ELT, I recommend you replace the antenna with one certified for 121.5 and 406 MHz (all 406 ELT antennas will work on 121.5). That way if you update the ELT later (e.g. when it fails) you won't need to change out the antenna.
 
gismo said:
Even if you keep your old ELT, I recommend you replace the antenna with one certified for 121.5 and 406 MHz (all 406 ELT antennas will work on 121.5). That way if you update the ELT later (e.g. when it fails) you won't need to change out the antenna.
Click to expand...

That makes great sense, and I would love to do it. I see 2 issues, though. As far as I have been able to read, the TSO for the AK-450 is specific to their one 121.5 antenna. No mention of the dual 121.5/406 antenna. So while it may work, I don't think the shop will install an antenna that does not comply with the TSO. I will call AK on Monday to see if they have a 121.5/406 antenna that is ok for the AK-450, just in case, though.

The other issue is that I would not want to replace my 450 with an AK-451 based on the consistently bad reviews given that unit and AK support. So that would mean that whatever other brand I purchase would have to accept the AK 121.5/406 antenna as compliant. But those that I have researched all come with both the ELT and their own antenna as part of the TSO's package. So the shop may insist that I have to change to another 121.5/406 antenna with a new non-AK ELT even if we install an AK 121.5/406 antenna next week. I will call ACK and Artex and see what they advise.

Thanks for the suggestion.
 
bkspero said:
No mention of the dual 121.5/406 antenna. So while it may work, I don't think the shop will install an antenna that does not comply with the TSO. I will call AK on Monday to see if they have a 121.5/406 antenna that is ok for the AK-450, just in case, though.

Thanks for the suggestion.
Click to expand...

That's a point that I've been pondering for this whole thread. Are you **absolutely** sure that the broken antenna is your ELT antenna? And not an obsolete LORAN antenna? Have you done a continuity check between the antenna ends and gotten positive confirmation that the antenna connected to the ELT is in fact the one connected to the antenna?

The reason I ask is that the old ELTs had to meet specification on both 121.5 AND 243.0 simultaneously. Trying to meet that spec without some sort of gimcrackery in the center of the antenna was nigh near impossible, and yet, you say it was a single spike antenna. Just for $#!ts and giggles, how LONG was that spike above the airframe?

Let's be sure we aren't chasing wild geese here.

Jim
 
weirdjim said:
That's a point that I've been pondering for this whole thread. Are you **absolutely** sure that the broken antenna is your ELT antenna?

Just for $#!ts and giggles, how LONG was that spike above the airframe?

Jim
Click to expand...

Jim, good point. To answer your question, the broken piece of the mast that I have at home is 17 3/4 inches long from the break to the top of the ca. 3/16 inch diameter loop at the top. My guess is that the broken stub extends about 1/4 inch above the skin of the fuselage. That could be as little as 1/8 inch or as much as 1/2 inch.

After looking online I see that 18 inches is about 5 inches shorter than 1/4 wave on 121.5 mHz. Could there be circuitry within the box at the base to compensate for the difference?

The easiest thing for me to do will be to look at the plane. I'll do that tomorrow. If you look at the photo in my original post, though, you can see a piece of black coax going from the box at the base of the broken antenna inside the fuselage towards the rear and through a hole in a rear bulkhead next to the ELT. The coax routing behind the bulkhead is blocked from view sufficiently that it isn't completely clear that this wire goes to the ELT, but the that seems to almost certainly to be the connection. There are several lighter colored wires running along the bottom of the fuselage. One of them also runs up towards the ELT. I am certain that one is the wire for the panel switch for the ELT.

The plane doesn't have any unaccounted for antennas (as far as I can see). VOR/ILS antennas trailing back from both sides of the top of the vertical stabilizer. The broken antenna which I think is the ELT. Another antenna on the top of the fuselage which the maintenance manual says is Comm2, the GPS antenna on the top of the fuselage ahead of the dorsal fin, a bent antenna on the bottom of the fuselage which the maintenance manual says is Comm1, and the stub antenna for the transponder on the bottom of the fuselage.

This information, plus the fact that the appearance of the broken antenna matches the type used in the original ELT in the plane (and none match the appearance of an AK ELT antenna), makes me pretty confident that the broken antenna served the ELT. But just in case, I will double check at the plane tomorrow.

Thanks for raising the issue, though. Would be really embarrassing to have the shop order an ELT antenna and when we open up the fuselage find that the broken one served something else (or nothing at all).
 
bkspero said:
Jim, good point. To answer your question, the broken piece of the mast that I have at home is 17 3/4 inches long from the break to the top of the ca. 3/16 inch diameter loop at the top. My guess is that the broken stub extends about 1/4 inch above the skin of the fuselage. That could be as little as 1/8 inch or as much as 1/2 inch..
Click to expand...

WOuldn't it be better to break open the fuselage and be SURE? Anyway ...

Would you like to make one for $5 that nobody except you knows is hand-made (unless you spill the beans)? You can certainly make one that is a hell of a lot better than that kludge you took off, and a lot sturdier ... AND you can paint and finish it to make it look original.

Just a random thought, although ** I ** would never put something that didn't have STC-PMA-TSO-PMS-RDT-AM-FM on MY airplane. No sir, not me, not never.

Jim
 
Checked the plane. It is the ELT antenna.
 
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