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  #1  
Old 07-31-2019, 02:34 AM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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Default Altitude Encoder...

I’m having a low-level Baro Alt problem with my uAvionix ADS-B installation. Most PAPR’s are good but some come back with close to 2% Baro Alt error and are marked red for failure. I talked with FAA ADS-B folks at Oshkosh last week and they said problem is intermittent with my altitude encoder reporting. So maybe encoder is bad or wiring problem. See post http://www.vansairforce.com/communit...2&postcount=21

My question…. I bought my 12 from original builder and I’m familiar with all the systems but I can’t figure out where the altitude encoder is located. I have early SN 12 with Garmin GTX-327 transponder and D-180 EFIS. I have looked at electrical schematic and construction drawings but have yet to find info on altitude encoder installation.

Any help appreciated. Thanks in advance…
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Jim Stricker
Hinckley, Ohio (1OA2)
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
RV-12 E-LSA #120058 AWC July 2012 N633CM
RV-12 Bought Flying Oct 2015 with 48TT - Hobbs now 490

LSRM-A Certificate 2016
Special Thanks... EJ Trucks - Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - 1st Lt. Captain B-17H
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  #2  
Old 07-31-2019, 04:55 AM
BigJohn BigJohn is offline
 
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Default

Its in the D-180.
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VAF paid through 10/2019.
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  #3  
Old 07-31-2019, 07:56 AM
Mich48041 Mich48041 is offline
 
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Location: Riley TWP MI
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Default

Most intermittent problems are due to bad connections.
Unnecessary altitude encoder connections can be eliminated in your plane by bypassing the control board.
To do that, connect Pin 13 of the D-180 EFIS 25 pin D-Sub to the transponder encoder input.
Also connect ground Pin 16 of the D-180 EFIS 25 pin D-Sub to a transponder ground.
The extra ground is redundant, but will not hurt anything.
The above may or may not fix the problem, but is worth a try.
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  #4  
Old 07-31-2019, 08:22 AM
moosepileit moosepileit is offline
 
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Location: Floyds Knobs, IN
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Default

At the minor risk of a mfgr drift a bit, this seems a good spot.

GRT Sport SX200 EFIS' encoder, built-in grey code harness wires to a KT-76A transponder.

What would likely cause cycling between 9500' and 9700' on ATC's altitude readout? Steady at 9500' matching ATC local altimeter. Pitot static system well calibrated.

40 miles to antenna. Small ball on stick antenna fwd right on belly near firewall, antenna ground site 3 o'clock relative to nose.

9500' was as high aa I flew and that was max on flight's PAPR: Baro Alt (ft): 400 - 9500

Grey codes- C2 and C4 are the last two digits in each string.

9500'= 000011111010
9700'= 000011111001

Table source: http://www.mglavionics.com/kb/articl...Reference.html
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Last edited by moosepileit : 07-31-2019 at 09:01 AM.
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  #5  
Old 07-31-2019, 08:55 AM
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DaleB DaleB is offline
 
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Location: Omaha, NE (KMLE)
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Jim,

It may not really an alt encoder problem. I recently installed a uAvionix EchoUAT and SkyFyx, and (surprise!!) have BARO ALT errors showing up in the PAPR. Unless you wired the serial data from the transponder to the uAvionix device, it monitors the transponder signal to grab the squawk and altitude data. There is a setting for the sensitivity of the transponder monitor. Here's a quote from the email I received from uAvionix support:

Quote:
Adjusting the threshold value on the echoUAT can improve the performance of the transponder monitor. uAvionix does not recommend changing the value unless directed to do so by uAvionix.

The threshold value adjusts the sensitivity of the echoUAT transponder monitor. Higher values reduce sensitivity, lower values increase sensitivity.

To modify the threshold value perform the following steps:
1. Turn the avionics master on.
2. Place the Transponder in "ALT" mode.
3. Connect a mobile device to the echoUAT Wi-Fi.
4. Open the echo mobile application.
5. Verify the app shows "Connected to Device"
6. Tap two fingers simultaneously on the echo logo.
7. Scroll to the bottom of the app screen and find the Transponder Threshold values.
8. Change the Transponder Threshold by -50 and press Update Advanced.
9. Switch to the Monitor screen and watch for pressure altitude and squawk.
Please note transponder must be receiving radar interrogations for the fields to populate. Most transponders have a reply light or indicator.
Note Mode S does not reply with pressure altitude in a ground state.
10. When the appropriate threshold has been reached the Squawk and Pressure altitude will display. Repeat 8 & 9 until ALL fields are populated
11. Values lower than 1100 should not be used and most installs seem to land between 1400-1600.
If you are still having difficulty and cannot get a reliable/stable readout please contact support@uavionix.com
Hope this helps.
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  #6  
Old 07-31-2019, 10:45 AM
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Piper J3 Piper J3 is offline
 
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Dale

Yes, I'm familiar with threshold monitor. I tried for several months to fine tune this setting with some good / some bad PAPR and finally decided to hard wire the transponder with uAvionix supplied MUX cable. So now I get a low incidence of Baro Alt failure. About one out of ten flights gets a red box on PAPR.

As a side note, I talked with FAA ADS-B specialist at Oshkosh last week and he said I should continue to try to fix the problem but FAA would not reprimand me if the problem doesn't get fixed. He said they consider this a low level problem.

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Jim Stricker
Hinckley, Ohio (1OA2)
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
RV-12 E-LSA #120058 AWC July 2012 N633CM
RV-12 Bought Flying Oct 2015 with 48TT - Hobbs now 490

LSRM-A Certificate 2016
Special Thanks... EJ Trucks - Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - 1st Lt. Captain B-17H
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  #7  
Old 07-31-2019, 10:46 AM
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Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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Quote:
Originally Posted by Mich48041 View Post
Most intermittent problems are due to bad connections.
Unnecessary altitude encoder connections can be eliminated in your plane by bypassing the control board.
To do that, connect Pin 13 of the D-180 EFIS 25 pin D-Sub to the transponder encoder input.
Also connect ground Pin 16 of the D-180 EFIS 25 pin D-Sub to a transponder ground.
The extra ground is redundant, but will not hurt anything.
The above may or may not fix the problem, but is worth a try.
Thanks Joe. I'll hold this information for future consideration...
__________________
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Jim Stricker
Hinckley, Ohio (1OA2)
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
RV-12 E-LSA #120058 AWC July 2012 N633CM
RV-12 Bought Flying Oct 2015 with 48TT - Hobbs now 490

LSRM-A Certificate 2016
Special Thanks... EJ Trucks - Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - 1st Lt. Captain B-17H
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  #8  
Old 07-31-2019, 10:51 AM
BigJohn BigJohn is offline
 
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Location: Gloversville, NY
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I believe that is old information. I have been told the boxes come out of the factory now with the threshold set at 1350. I had to go lower to get good ops.

On some transponders you can trigger an output for testing purposes by tweaking the mode knob into the “test” position.

My observation is that the Baro Out data is the first thing to fail if you are in a marginal coverage area.

If you have a good passing PAPR in your file to show compliance then why worry about an occasional 2% error?
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“Master Pilot” Award, UFO Member.
RV-12 N37JP 120176 Flying since 2012.
One Week Wonder Build Team, OSH 2018.
VAF paid through 10/2019.
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  #9  
Old 07-31-2019, 12:15 PM
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Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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Quote:
Originally Posted by BigJohn View Post
If you have a good passing PAPR in your file to show compliance then why worry about an occasional 2% error?
A few reasons I can think of...
  • Equipment might continue to deteriorate.
  • Maybe Big Brother (FAA) will not be lenient in the future.
  • I like everything working 100% correct.
__________________
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Jim Stricker
Hinckley, Ohio (1OA2)
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
RV-12 E-LSA #120058 AWC July 2012 N633CM
RV-12 Bought Flying Oct 2015 with 48TT - Hobbs now 490

LSRM-A Certificate 2016
Special Thanks... EJ Trucks - Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - 1st Lt. Captain B-17H
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