ACK E-04 ELT remote transmit light intermittently illuminates

[Steve Knoblock]

Anyone else had to deal with the red remote "ELT TRANSMITTING" light occasionally showing the ELT is transmitting? Every now and then, mine does this (1-2 times every other flight or so). I monitor 121.5 and never hear the ELT, and I have called the AF Rescue center to see if they were getting a signal (they were not). It's a false indication.

I talked to ACK engineering and they think it might be EMI induced at the audio alert connection or at the remote control panel itself. The issue only started after I installed an EI MVP-50 engine analyzer, so I think it's a plausible explanation. Believe it or not, the recommendation was to use some aluminum foil around the connections to shield them................

 

[Daleandee]

When was the last time the battery in the remote was tested/replaced?

 

[Steve Knoblock]

Worthwhile question for folks reading the thread

in my case, all batteries were replaced last year, but the false alerts were happening both before and after battery change

 

[NoHeat]

Google readily finds the installation manual, PDF format, on the manufacturer's website.

Page 9 has this, for the cable to the remote indicator (RCPI)

Run the short audio alert cable from the RCPI to the audio alert module (page 6 Fig. 8) avoid running this cable near
sources of strong EMI/RFI radiation. (i.e. Comm cables, strobe light power cables, starter cables.)

So I'd start by testing what you can turn off that makes the problem go away. Strobe light, for example.

Then look at the cable routing, and see if you can move that cable. Maybe it got moved when your engine monitor was installed.

Adding aluminum foil to a connector is too Mickey-Mouse. If it works at first, what about when the foil falls off?

 

[Steve Knoblock]

Nice catch! I hadn’t noticed that in the manual, and that would explain the engineer’s jump to the EMI cause. Guess this system might have some EMC issues

My MVP50 is installed on the right side of the cockpit, and the RCP is just outboard of that. The data collection unit for the MVP50 is mounted back there too, so all of the sensor wires are back there too. I can certainly adjust the ELT wiring routing to see if there’s an improvement.

thanks guys!

 

[NoHeat]

In the engine compartment, are the sensor probe wires positioned near the spark plug wires or magneto?

I'd guess those wires might be acting as antennae that capture radio-frequency noise from the intense brief currents in the nearby spark-plug wires. I suppose if you see the ELT remote light flickering during run-up, and if it diminishes immediately after the run-up or stops immediately when you pull the mixture to stop the engine, that might indicate exactly that spark is the source, and your sensor probe wires is bringing that RF noise right near your remote ELT indicator in the cabin.

 

[flyingron]

When was the last time the battery in the remote was tested/replaced?

The battery does nothing other than make the LEDs light up.
Make sure that the thing was installed right to begin with. You put the connectors on upside down, you'll get loopy behavior.

 

[Dan Thomas]

I had an ACK E-04 that wanted to trigger on certain com frequencies. I fixed when when I did what the avionics techs suggested: Install a ferrite core over the remote switch cable right up close to the ELT. (Sometimes called ferrite beads, ferrite chokes, ferrite suppressors.) It creates an inductive resistance to the stray RF that is triggering the ELT.

 

[Daleandee]

The battery does nothing other than make the LEDs light up.
Make sure that the thing was installed right to begin with. You put the connectors on upside down, you'll get loopy behavior.

Agreed, but he noted that it wasn't actually transmitting just that the light was coming on periodically. I don't know that a low battery wouldn't cause some kind of fault so it's just a guess. But a replacement battery isn't much and should be replaced/dated during inspection.

I see that the OP has already covered that.

 

[Steve Knoblock]

Some great ideas here. I like the ferrite core idea. Amazon seems to have them cheap. Might be better than aluminum foil!

As far as the magneto idea - not sure how that might apply here. The MVP50 uses the ignition switch to track RPM, so it there shouldn’t be any real voltage going there

BTW, this is my installation

 

[Dan Thomas]

As far as the magneto idea - not sure how that might apply here. The MVP50 uses the ignition switch to track RPM, so it there shouldn’t be any real voltage going there

There's no real current flow, but the voltage can be significant. It's more than the 14 volts in your car's ignition primary. And it has sharp voltage spikes to it, which is why it's such a great broadband radio transmitter if the P-leads aren't shielded. The ELT remote wire might be picking something up off the MVPs tach input wiring. They should have the isolators on them if you have magnetos or CDI and not a standalone electronic ignition. Are they there? From the manual:

 

[flyingron]

Agreed, but he noted that it wasn't actually transmitting just that the light was coming on periodically. I don't know that a low battery wouldn't cause some kind of fault so it's just a guess. But a replacement battery isn't much and should be replaced/dated during inspection.

I see that the OP has already covered that.

The remote is pretty dirt simple. I ended up debugging the thing when I put my plane back together. There are four wires going to it. One is the common. Two of them are just the buttons (short to common). The third is the light which goes through the LED, the battery, and then back to common.

The problem is the silly thing uses a regular telephone cord for the interface. Every RJ11 connector can be put on in one of two orientations on the cord. Get it wrong, and the thing will intermittently trip the ELT. Obviously, not the problem here, but in case anybody ever gets stuck trying to debug this. Amusingly, I'm sitting out in Bumfart Nebraska where the only place in town is some little hardware store. I ended up screwing around with some telephone two-for adapters that flipped it around until I could get somewhere (like home) where I had the tools to redo the plug.

 

[Daleandee]

The problem is the silly thing uses a regular telephone cord for the interface. Every RJ11 connector can be put on in one of two orientations on the cord. Get it wrong, and the thing will intermittently trip the ELT. Obviously, not the problem here, but in case anybody ever gets stuck trying to debug this. Amusingly, I'm sitting out in Bumfart Nebraska where the only place in town is some little hardware store. I ended up screwing around with some telephone two-for adapters that flipped it around until I could get somewhere (like home) where I had the tools to redo the plug.

I almost brought that point up in my previous post but deleted it. I learned that lesson building my current airplane as I wanted a shorter cable from the unit to the remote. Using a standard RJ11 did exactly as you stated. A friend had the needed tool to shorten the existing cable.

 

[Steve Knoblock]

Never thought my question would generate such good banter. Love it! Thanks everyone for weighing in.

I’ll have to check my MVP install for the isolators, but my guess is there are there. I have flown the plane almost 300 hours since the install and I’ve not had any RPM indication issues.

just flew the plane tonite for an hour or so and there was no ELT bad behavior. Guess I’ll just start coordinating my powerball/megamillions purchases for the days it happens

 

[kshaw]

The older versions of this ELT have a technical service bulletin that requires a static suppressor on the antenna. If your antenna requires it, get it and see if this solves your problem.

 

[wilkersk]

I really don't like the RJ11 connections and telephone cable that runs between the ELT and the remote. I don't understand why they did it that way.