Troubles with Landing Height System

[AndreiC]

About 6 month ago I had an LHS installed on my M20E (rev C, the one that warns also of landing gear not being lowered). Ever since the beginning the system has worked intermittently. Even when they installed it, the avionics shop thought the audio panel (a KA134) must have had a dirty contact in the MKR switch, cleaned that up, and said it was good to go. (The audio output is fed through the old Marker Beacon channel that was removed.)
 

Since then it’s been working about half the time. When I turn it on I can always hear the greeting message, but half the time I get nothing at all when landing. A few times it gave me correct readings below 70 ft only. The rest of the time it either works perfectly (about half the landings) or it says nothing all the way to the ground. 

I thought it must be the audio panel that was faulty, but I spent $150 to get a replacement one on ebay, and the new one behaves just like the old one: half the time it works great, half it is totally quiet. 

Has anyone else had a similar problem? Where should I begin to debug it?

[toto]

Might be worth pulling in the expert here, since you’ve already spent money on a hardware fix ..

@Microkit

[LANCECASPER]

36 minutes ago, AndreiC said:

About 6 month ago I had an LHS installed on my M20E (rev C, the one that warns also of landing gear not being lowered). Ever since the beginning the system has worked intermittently. Even when they installed it, the avionics shop thought the audio panel (a KA134) must have had a dirty contact in the MKR switch, cleaned that up, and said it was good to go. (The audio output is fed through the old Marker Beacon channel that was removed.)
 

Since then it’s been working about half the time. When I turn it on I can always hear the greeting message, but half the time I get nothing at all when landing. A few times it gave me correct readings below 70 ft only. The rest of the time it either works perfectly (about half the landings) or it says nothing all the way to the ground. 

I thought it must be the audio panel that was faulty, but I spent $150 to get a replacement one on ebay, and the new one behaves just like the old one: half the time it works great, half it is totally quiet. 

Has anyone else had a similar problem? Where should I begin to debug it?

My bet is wiring is incorrect. I've had two of the LHS in two different airplanes and they both worked fine.

[alexz]

Mine does the same. About 1/3 of the landings I don’t hear count until last 10 or 5 announcement. System was installed by very good shop. 

[GeeBee]

Did you try cleaning the lens?

[Yetti]

Did you contact the manufacture support?  I would think there is a calibration or self test routine.

 

  When driving in the snow muck in Colorado my truck informed me that the Front Camera was dirty.    My thought was "Why tell me and expect me to do something about it.   Clean it yourself fancy truck"

[dkkim73]

Mine (installed when I bought it) has been flawless and very useful... If the audio fix was not decisive perhaps there is a bad ground or similar issue? Perhaps microkit can look at logs and see if there's any erratic data that would shed light on the dirty window hypothesis. 

BTW Mooney did the install, they were very thorough on the installation and the documentation of the installation. 

[alexz]

8 hours ago, GeeBee said:

Did you try cleaning the lens?

I use similar devices on the drones and never needed lens cleaning for laser powered device. Lenses usually protected by front filter for expected wavelength which seems to be done in LHS as well. And that surface is clean on my install. System does work most of the time so i don’t want to spend time/money on figuring what is wrong when it does not work. Typically on a systems like that we have a recorded log of data for the last 30 minutes but it adds to the cost of the system to do the logging reliably and/or not to wear flash storage too quickly.  

[RoundTwo]

1 hour ago, alexz said:

I use similar devices on the drones and never needed lens cleaning for laser powered device. Lenses usually protected by front filter for expected wavelength which seems to be done in LHS as well. And that surface is clean on my install. System does work most of the time so i don’t want to spend time/money on figuring what is wrong when it does not work. Typically on a systems like that we have a recorded log of data for the last 30 minutes but it adds to the cost of the system to do the logging reliably and/or not to wear flash storage too quickly.  

How about using the built in Wi-Fi interface to test it in flight? It’s an unorthodox approach, but it may work. (This would best done with two people)

The Wi-Fi interface runs for 5 minutes after startup, so when you are within 5 minutes of landing, cycle power to the unit and attempt to log into it. If connection works, you could trigger alerts and also see it’s observed height.

If you do this, please let us know how it works.

 

[Pinecone]

I would call MicroKit.

Mine has been perfect.

[GeeBee]

2 hours ago, alexz said:

I use similar devices on the drones and never needed lens cleaning for laser powered device. Lenses usually protected by front filter for expected wavelength which seems to be done in LHS as well. And that surface is clean on my install. System does work most of the time so i don’t want to spend time/money on figuring what is wrong when it does not work. Typically on a systems like that we have a recorded log of data for the last 30 minutes but it adds to the cost of the system to do the logging reliably and/or not to wear flash storage too quickly.  

Most drones don’t have an oil breather with a propeller in front of it. I find when I clean mine with some alcohol performance improves 

[exM20K]

17 hours ago, alexz said:

Mine does the same. About 1/3 of the landings I don’t hear count until last 10 or 5 announcement. System was installed by very good shop. 

Mine did the same. Microkit was very quick to respond.  Mine is mounted on the fuselage, just inboard of the step.  It does get LOP exhaust residue on it in that location from time to time, and when it does, the behavior is as you describe.  A quick wipe, and all is good.

-dan

[kortopates]

Mine did the same. Microkit was very quick to respond.  Mine is mounted on the fuselage, just inboard of the step.  It does get LOP exhaust residue on it in that location from time to time, and when it does, the behavior is as you describe.  A quick wipe, and all is good.
-dan

Mine is installed out on the wing impervious to exhaust & oil residue and has been flawless. If this issue gets to anyone consider moving it outboard to eliminate this issue.

i do have to turn it off whenever going IMC since it will start reporting about ~3’ repeatedly as soon as entering the clouds which is a bit unsettling with pax aboard as well as a nuisance.


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[exM20K]

1 hour ago, kortopates said:

Mine is installed out on the wing impervious to exhaust & oil residue and has been flawless. If this issue gets to anyone consider moving it outboard to eliminate this issue.

i do have to turn it off whenever going IMC since it will start reporting about ~3’ repeatedly as soon as entering the clouds which is a bit unsettling with pax aboard as well as a nuisance.


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I think there is a software update to fix this.  Mine doesn'tdo this.

-dan

[RoundTwo]

56 minutes ago, exM20K said:

I think there is a software update to fix this.  Mine doesn'tdo this.

-dan

They use a gps speed feed with a setting for a threshold. You have to be flying slower than the threshold speed in order for it to know you’re landing and it will alert. 

[kortopates]

I think there is a software update to fix this.  Mine doesn'tdo this.
-dan

I don’t have the latest version so will have to check that out. thanks!
But if i need a GPS feed iam out of luck as mine is only connected to audio output.

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[Pinecone]

I think it only one more wire.