Altitude reporting issue

[0TreeLemur]

Howdy everyone,

 

[midlifeflyer]

Howdy to you too.

[0TreeLemur]

I hate it when this happens.  I just typed in a long explanation of my problem and it disappeared...   Grrrrr.

In late June my mode C and ADS-B reported elevation became a random number generator.   I bought a used working Terra AT3000 encoder off eBay, plugged it in, and it made no difference on a test flight.   So it is the cable/connector or Appareo xponder.  

Here is a photo I took yesterday evening in my hangar, which is at 175 ft elev.   Obviously something wrong.  I don't think that is the correct Gray code for -1100 ft either.  Something is seriously wrong.   Any ideas?  Wouldn't the Appareo throw and error flag if it detected an internal problem?   I don't see any error flags.

All the avionics shops in my area are busy and/or focused on high $$ upgrades, not minor repairs to 52 y.o. Mooneys...  Any help appreciated.

 

Edited July 15, 2019 by Fred₂O
spelling.

[carusoam]

It’s ok, I wrote an answer before the question came available....

Am i close?

Well...

1) Altitude reporting starts with the static system...

2) connects to the altimeter...

3) turns into data via the encoder...

4) The encoder sends the data to the transponder...

5) the transponder rats you out to everyone that is looking... (if you have a challenge)

6) Leaks are a usual challenge...

Unfinished answer of a PP, not a mechanic...

Best regards,

-a-

Looking back at the actual question, I feel pretty confident my answer wasn’t going to get any better... 

[N201MKTurbo]

It depends on how your encoder is wired. If it has a gray code connection, an open wire can cause that type of error and your transponder will not be able to detect it. If you have a modern encoder with a serial connection, it can detect a loss of signal. 

Have your avionics guy hook his transponder tester to it along with his static tester and run it up, he will be able to tell you which wire is broken in short order.

Or inspect the wiring yourself if you have those skills.

[0TreeLemur]

It reports a "parallel" connection, which is what the old Terra AT3000 would support.   Those are 1970's encoders.    Might be a broken wire/connector issue.   The problem is, as I said, the one Avionics shop within a reasonable distance of me is too busy.  

[Browncbr1]

Ring out all your pins to make sure you don’t have any wires backwards, which is easy with so many Gray code connections.    If all pins/connections are correct.    Are any of your wires shielded?

if you end up needing it, I have a nice Sandia SAE5-35 encoder on my shelf that is like new with connector.   It has about 100hrs on it and it was always spot on, but I pulled it to to install a tt22 adsb out transponder that has an encoder built in.  

[Baker Avionics]

On 7/15/2019 at 1:32 PM, Fred₂O said:

It reports a "parallel" connection, which is what the old Terra AT3000 would support.   Those are 1970's encoders.    Might be a broken wire/connector issue.   The problem is, as I said, the one Avionics shop within a reasonable distance of me is too busy.  

Where are you located?  We can help.  We are ahead of schedule and can start fitting folks in as needed.  I have noticed that these other issues are falling by the wayside.  

[Oldguy]

6 minutes ago, Baker Avionics said:

Where are you located?  We can help.  We are ahead of schedule and can start fitting folks in as needed.  I have noticed that these other issues are falling by the wayside.  

He might be a little too far to run it over to you - Tuscaloosa, Alabama.

[Baker Avionics]

Just now, Oldguy said:

He might be a little too far to run it over to you - Tuscaloosa, Alabama.

Hey, you have a Mooney for a reason don't you?  LOL

[steingar]

Have you contacted Appareo about the matter?  I've one of those sitting in my panel and to the  best of my knowledge its worked flawlessly.

[takair]

Fred

do you recall what the pressure altitude was when you took the picture or what the baron setting was?  

[0TreeLemur]

Today I took my airplane to the company that installed the Appareo last year.  A big shout out to Jerry and Jason of Deep South Avionics in Okolona, Mississippi, for meeting me on a Saturday.   They believe in supporting what they sell and install.

It turns out that that the problem was a finicky connection at the back of the transponder where it plugs into the tray.   It seems that the range of error is small given the length of the pins and positioning of the female D-connector in the back of the tray.   It must be installed within about less than 1 mm tolerance. 

My take home message is: 1) don't fill your 430W and KX155 with water by using an appropriate sealant on the instrument bay; and 2) don't pull out the Appareo transponder if it is working.   The good news is that it all passed muster (encoder, static test, and ADS-B out).    I'm relieved.  Coming back it worked flawlessly.

[carusoam]

Great follow-up Fred₂...

Thanks for sharing the results.

Best regards,

-a-

[0TreeLemur]

On 7/15/2019 at 3:04 PM, Fred₂O said:

I hate it when this happens.  I just typed in a long explanation of my problem and it disappeared...   Grrrrr.

In late June my mode C and ADS-B reported elevation became a random number generator.   I bought a used working Terra AT3000 encoder off eBay, plugged it in, and it made no difference on a test flight.   So it is the cable/connector or Appareo xponder.  

Here is a photo I took yesterday evening in my hangar, which is at 175 ft elev.   Obviously something wrong.  I don't think that is the correct Gray code for -1100 ft either.  Something is seriously wrong.   Any ideas?  Wouldn't the Appareo throw and error flag if it detected an internal problem?   I don't see any error flags.

All the avionics shops in my area are busy and/or focused on high $$ upgrades, not minor repairs to 52 y.o. Mooneys...  Any help appreciated.

 

For the record and others who come upon this thread- the indication shown in the photo is what the Appareo transponder says when it receives no data from an encoder.  That is not the correct Gray code for -1100 ft elevation.   All 0's on the Gray code and -1100 ft indication is Appareo's way of saying "I'm not getting any elevation data from an encoder".  I this case, it was because the transponder was not making appropriate contact with the connectors in the back of the tray- particularly the "D" connector on the back right-hand side.   Proper re-installation by an experienced installer solved the problem.

[carusoam]

Nice detailed follow-up, Fred!

Thanks for sharing...

Best regards,

-a-