Deviation from magenta line in GPSS (GTN750, KAP 150 and GDC31 GPSS)

[M252]

However, the plane actually remained left of the "localizer" and you are right pics taken after coupling after FAF.

[jclemens]

Hand flying the same approach results in centered needles and airplane on magenta line?  Get your autopilot aligned by someone who knows what they are doing.

[M252]

Yes, that is right, hand flying works with centered needles on the magenta line. I will fly to the best avionics shop that we have over here. Thanks again

[carusoam]

M252,

you may want to update your avatar with your location info.  People can tell you what shops they have used near you if they have a feeling for where you are...

Best regards,

-a-

[jclemens]

Germany....didn't see that coming.  

 

[N201MKTurbo]

On ‎5‎/‎13‎/‎2016 at 11:30 AM, M252 said:

Thanks jlunseth.

- Next time I will leave the GDC31 in GPS mode. One very helpful thing I learned today :-) thanks again.

- I am also confused why the AP banks to the wrong side. I will ask an AP expert next week.  I have observed this several times... I will post what I find...

The control system (autopilot) has a function called an integrator. This is an internal variable that changes over time to take out any gain error. When you change the source of the error signal, such as changing the autopilot mode, the error signal will instantly change, but the integrator will not change instantly, it will change over time.

Do you have the autopilot in heading mode when you switch to GPSS? If not the autopilot will be trying to correct for the nav error while the GPSS is steering it with pseudo heading errors. 

[M252]

On 15.5.2016 at 6:13 PM, N201MKTurbo said:

Do you have the autopilot in heading mode when you switch to GPSS? If not the autopilot will be trying to correct for the nav error while the GPSS is steering it with pseudo heading errors. 

Yes, the KAP150 is in HDG mode for both HDG and GPS on the A/P selector of the GDC31.

On 15.5.2016 at 4:12 AM, jclemens said:

Germany....didn't see that coming.  

??, your surname is German :-)

The best avionics shop on this side of the Atlantic is Avionik Straubing in the southern part of the country - I will  talk to them.

[jclemens]

Yes it is   I was going to suggest locations to take it to have it fixed, but I have no avionics connections there.  We are an Aspen dealer and by association I guess an Avionik Straubing dealer.  I put one of their altitude preselect units in our 231, works great.  I do have some contacts over at the Austro plant if you need turbo diesel support. 

[M252]

Thank you jclemens, I will share the result once I have it. May take a couple of weeks...

A diesel engine would be great if it can replace the TSI-360 in our Mooney M20K . Don't see that coming any time, soon.

[gsengle]

I had this very same problem with King flight director and autopilot and Garmin GPS. My problem may not be the same as your problem, but in my case it was a sign of impending failure of the artificial horizon. What was happening was the failing attitude indicator was leaning in one direction and then the autopilot was commanding flight in the other direction in order to get back to where I thought it needed to be. What this resulted in was stable level flight to one side of the magenta one. However eventually it was clear what was going on because the AI failed. How long is it been since your AI has been overhauled?

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[M252]

That is interesting! My AI was actually bench-checked last winter and was OK (it is only ~150 h after the last overhaul). So it seems that A/P misalignment and/or the GDC31 could be my issue.

[gsengle]

They just slowly fail, a year old bench check wouldn't mean anything. Go up in VFR conditions and make sure your AI is working crisply as you expect it to and you'd rule that out...

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