Help finding intercom noise when gear is up

[dfurst]

I recently installed a digital ignition.  Works great, easier starts, smoother engine.  Don't have enough data yet to tell if I am getting better performance.

 

One strange annoyance is there is now a loud noise in my headset.  The noise does not start until I start raising my gear, then stays once the gear is up.  When I lower the gear, the noise stays until down and locked, then the noise goes away.

Trouble shooting so far

- Flying straight and level, noise is there

- - Turn off digital ignition.  Noise goes away.  Turn it back on.  Noise comes back.  We know the source, but not the route.

-- Turn of remaining mag, noise stays.

-- Turn off com 2.  noise stays.

-- Not sure how to turn off GTN650?  I guess I could have pulled the CB.  Next time.

-- Lower gear.  Noise stays until down and locked, then quiet.

Digital ignition company said check all the grounds.  The shop has double checked all the grounds on the new ignition.  They have confirmed it is grounded to the frame and not grounded on the same ground as any avionics or intercom.  The next step is to swap out components of the digital ignition, but we doubt that is going to do anything as the noise is not there when gear is down and locked.

 

Any ideas?  Advice?

 

Thanks!!

[PeteMc]

Any chance there's a problem with one of the Up Contact Switches for the gear and the motor still has a load on it?  That could cause a lot of interference and eventually burn out the motor.  (Pending the motor and if it's well built, it could run that way for quite a while before it burns out.)

[dfurst]

1 hour ago, PeteMc said:

Any chance there's a problem with one of the Up Contact Switches for the gear and the motor still has a load on it?  That could cause a lot of interference and eventually burn out the motor.  (Pending the motor and if it's well built, it could run that way for quite a while before it burns out.)

Nice thought.  I do wonder if there is a problem with the signal from the landing gear. If there was a problem with the motor wouldn't that problem have been there all along?  And why would that noise stop when you turn the Digital Ignition off?

[mooniac15u]

Have you listened for the noise with the squelch turned off on the intercom?  If not, is it possible both the ignition and gear motor are making noise and it only breaks the squelch with the cumulative noise?

Have you tried turning off the intercom and seeing if the noise persists?  Usually there's a failsafe mode or second set of jacks that bypasses the intercom and connects straight to your com radio.  Do you hear the noise there also?

[1980Mooney]

46 minutes ago, dfurst said:

Nice thought.  I do wonder if there is a problem with the signal from the landing gear. If there was a problem with the motor wouldn't that problem have been there all along?  And why would that noise stop when you turn the Digital Ignition off?

You can easily rule out the landing gear motor by pulling the gear actuator circuit breaker when you have the landing gear up - no power - no chance of load. Watch the ammeter and voltage when you cycle the breaker also. If the up limit switch is bad then you should see the load pull the ammeter needle a little and volts drop slightly when you push the breaker back in. Also see if it alters the static. 
 

It bet you have already isolated the source. - your new ignition. 

Edited April 29, 2022 by 1980Mooney

[N201MKTurbo]

Humm...

What is different with the gear down? Electrically, not much. The only thing is the gear down and gear unsafe lights go out. Saying they have checked all the grounds, is a lot to ask of an aircraft mechanic. Most have limited electronic skills. Are the grounds grounded to the engine or the airframe? Is the engine well grounded to the airframe? What about the avionics? Are they properly grounded? Ideally a star ground to the steel tubes. Mechanically, the only thing I can think of is the nose gear puts some stress on the steel tubes near the motor mounts that may influence the engine grounding. 

[EricJ]

+1 on triple checking grounds.  Both for solid mechanical connection as well as clean electrical connection.    It might be grounds around the electric gear system or somewhere unexpected.

I'd suggest putting it up on jacks and trying it during gear swings.   It might take taking the belly off and trying manually engaging the down limit switch while the gear is up or things like that in order to try isolate what is different about the gear being down.  

[dfurst]

2 hours ago, mooniac15u said:

Have you listened for the noise with the squelch turned off on the intercom?  If not, is it possible both the ignition and gear motor are making noise and it only breaks the squelch with the cumulative noise?

Have you tried turning off the intercom and seeing if the noise persists?  Usually there's a failsafe mode or second set of jacks that bypasses the intercom and connects straight to your com radio.  Do you hear the noise there also?

No, didn't try the squelch in the intercom.  Will do.  Thanks!

I have turned the intercom off and the noise does go away.  Told avionics shop this and they say the intercom will amplify any noise, this does not mean the intercom is bad.  Avionics shop is looking at this too. Thanks!

Edited April 29, 2022 by dfurst

[dfurst]

2 hours ago, 1980Mooney said:

You can easily rule out the landing gear motor by pulling the gear actuator circuit breaker when you have the landing gear up - no power - no chance of load. Watch the ammeter and voltage when you cycle the breaker also. If the up limit switch is bad then you should see the load pull the ammeter needle a little and volts drop slightly when you push the breaker back in. Also see if it alters the static. 
 

It bet you have already isolated the source. - your new ignition. 

Good idea on pulling CB for landing gear.  Will try. Thanks.

Yes, I know the new ignition is the source.  The question is why only with gear in motion or up.

[dfurst]

1 hour ago, N201MKTurbo said:

Humm...

What is different with the gear down? Electrically, not much. The only thing is the gear down and gear unsafe lights go out. Saying they have checked all the grounds, is a lot to ask of an aircraft mechanic. Most have limited electronic skills. Are the grounds grounded to the engine or the airframe? Is the engine well grounded to the airframe? What about the avionics? Are they properly grounded? Ideally a star ground to the steel tubes. Mechanically, the only thing I can think of is the nose gear puts some stress on the steel tubes near the motor mounts that may influence the engine grounding. 

I should have been more specific on who is testing the grounding.  First pass the mechanic rechecked all the grounds.  Since then I have taken it to an avionics shop. The avionics guys would agree with you about mechanics and grounding. The 2nd review of the grounding was by the avionics shop and they confirmed the ignition is properly grounded. 

Nice thought on engine grounding.  Will suggest it.

[dfurst]

1 hour ago, EricJ said:

+1 on triple checking grounds.  Both for solid mechanical connection as well as clean electrical connection.    It might be grounds around the electric gear system or somewhere unexpected.

I'd suggest putting it up on jacks and trying it during gear swings.   It might take taking the belly off and trying manually engaging the down limit switch while the gear is up or things like that in order to try isolate what is different about the gear being down.  

Thought about putting it on jacks but noise only happens with engine running.  Not sure how safe it is to start an airplane engine while on jacks?

[dfurst]

One data point I left out.  When I was flying and lowered the power low enough for the gear warning horn to go off, the noise went away.

[PeteMc]

So not that it can't be something else...   But we're back to the Gear circuitry as a place for you to focus on first.

[1980Mooney]

45 minutes ago, dfurst said:

Thought about putting it on jacks but noise only happens with engine running.  Not sure how safe it is to start an airplane engine while on jacks?

NO!!!!!

IT WILL TIP OFF THE JACKS, IF THE GEAR ARE UP THEN PROP STRIKE. IF THE GEAR ARE DOWN PROBABLY FIRST STRIKE THE PROP AND THEN CAREEN INTO SOMETHING OR KILL SOMEBODY 

Edited April 29, 2022 by 1980Mooney

[EricJ]

49 minutes ago, dfurst said:

Thought about putting it on jacks but noise only happens with engine running.  Not sure how safe it is to start an airplane engine while on jacks?

That's a reasonable point. 

 

[carusoam]

Let’s take some mystery out of the situation… which digital ignition do you have?

There are two electronic ignitions around here… one is quite popular… the other one comes without a good pirep yet…
 

+1 for Jacks being designed as a gravity system…

Their bases are designed to be as narrow as possible… for stability, but not getting in the way…

A prop pulling on the plane may add an unexpected fall from the jacks…

Turning on the ignition without starting the plane may have the same affect…

+1 for reviewing all of the ground wires from engine to instrument panel and everywhere else…

 

Odd that the landing gear has anything to do with the sound caused by a mag… have to really think about that one…

Where does the new ignition system get its power from, and where is it grounded?

Some are running power wires from the engine to the battery in the tail… possibly going right past the gear….

PP thoughts only, not a mechanic…

Best regards,

-a-

[dfurst]

On 4/30/2022 at 12:12 AM, carusoam said:

Let’s take some mystery out of the situation… which digital ignition do you have?

There are two electronic ignitions around here… one is quite popular… the other one comes without a good pirep yet…
 

+1 for Jacks being designed as a gravity system…

Their bases are designed to be as narrow as possible… for stability, but not getting in the way…

A prop pulling on the plane may add an unexpected fall from the jacks…

Turning on the ignition without starting the plane may have the same affect…

+1 for reviewing all of the ground wires from engine to instrument panel and everywhere else…

 

Odd that the landing gear has anything to do with the sound caused by a mag… have to really think about that one…

Where does the new ignition system get its power from, and where is it grounded?

Some are running power wires from the engine to the battery in the tail… possibly going right past the gear….

PP thoughts only, not a mechanic…

Best regards,

-a-

It is the Eltroair EIS-61000-1M.  I assume this is the on one you are referring to as the "other one".  I compared the systems and I liked some of the features of the Eltroair over others.  I may be paying the price for that, but so far, noise aside, it has been good.  Starts are easy, engine runs smoother.  Don't know if I have any performance improvement as I have not had a chance to collect any data.

I am torn.  if this was an Electroair problem, it would be happening all the time, not just with the gear in motion and up.  Now, that being said, if they cannot figure it out I will be forced to go with another option. As you said, "Odd that the landing gear has anything to do with the sound caused by a mag"  Really has me stumped.

Now that Avionics shop has confirmed the EIS grounds are good, they are checking the rest of the grounds.  Also ordered a replacement 

 

  

[dfurst]

So, more data.

Took it for a test flight with the avionics guy. Pulled every single circuit breaker, one a at a time.  The only time the noise went away is when we pulled the intercom CB, which makes sense, because you can't hear anything if the intercom is off. 

BTW, side note, it is a good exercise to try this with another pilot with you.  I leaned a lot about what happens when various CBs pop, and what it takes to really shut down a 650.  I am now much more comfortable with what will happen if I ever have to pull a CB on purpoase.

 

A couple of things that struck the avionics guy as odd

1) Gear warning horn came through intercom

2) AP disconnect (very loud) came through intercom

3) Stall warning horn came through intercom

In his opinion none of those sounds come through the intercom in a stock Mooney.  Can someone confirm that is the case?  I did some quick Googling and from what I see, he is right.  All 3 of those are actual aural warnings, outside the intercom.  

The reason this is important is someone most have modified some systems or added a third party device to route these sounds via the intercom.  If this is the case, he wants to find that device and make sure it is not causing the problem, or remove it and rever these sounds back to their normal hardware.

[Fly Boomer]

1 hour ago, dfurst said:

A couple of things that struck the avionics guy as odd

Please let us know what he finds.  I thought those things were connected to Sonalerts.

[PT20J]

Early Mooneys just had sonalerts for the gear and stall warnings. Later ones (like my '94 J) have a tone generator that emits the sound through an overhead speaker (not the same one connected to the audio panel) and also through an unswitched input to the audio panel so that the tones are heard in the headset. If your overhead panel has two speakers rather than a bunch of sonalerts, then you have this setup.

The same applies to some autopilots. The original KAP 150 in my plane came with an overhead sonalert. However, the GFC 500 is wired to an unswitched input on the audio panel. 

Skip

[Fly Boomer]

1 minute ago, PT20J said:

Early Mooneys just had sonalerts for the gear and stall warnings. Later ones (like my '94 J) have a tone generator

How about a 1989 K?  I have no idea what I've got.

[PT20J]

1 minute ago, Fly Boomer said:

How about a 1989 K?  I have no idea what I've got.

 

3 minutes ago, PT20J said:

If your overhead panel has two speakers rather than a bunch of sonalerts, then you have this setup.

[Fly Boomer]

7 minutes ago, PT20J said:

If your overhead panel has two speakers rather than a bunch of sonalerts, then you have this setup.

To be clear, you mean two speakers instead of one?  I thought the Sonalerts (if they are there) would be hidden from view?

[PT20J]

17 minutes ago, Fly Boomer said:

To be clear, you mean two speakers instead of one?  I thought the Sonalerts (if they are there) would be hidden from view?

Yes. One speaker is connected to the audio panel for radio audio. The other is connected to the tone generator for the warnings. Sonalerts, if installed  protrude through the plastic headliner and are visible. If you tape the stall warning vane up temporarily and turn the master switch on, you can tell where the sound comes from. If you have the tone generator, it will come from the overhead speaker. If you also turn the radio master on you should hear it through the headset.

Skip

[Fly Boomer]

2 hours ago, PT20J said:

Yes. One speaker is connected to the audio panel for radio audio. The other is connected to the tone generator for the warnings. Sonalerts, if installed  protrude through the plastic headliner and are visible. If you tape the stall warning vane up temporarily and turn the master switch on, you can tell where the sound comes from. If you have the tone generator, it will come from the overhead speaker. If you also turn the radio master on you should hear it through the headset.

Ah, this is actionable.  Now I know what to do.  Thanks!