Trouble shooting Stec 30 Autopilot

[wpbarnar]

I have a Stec 30, GTN 650, and Aspen with GPSS.   Although the airplane gets flown weekly,  the autopilot is not used as often.  This past weekend on a trip, I discovered the AP:

1) with AP in track mode {high or low) it will not track the CDI.  Doesn’t matter if the GPS or VOR is driving the CDI, the AP will not track.  Not even attempt or hunt, the airplane will circle to the right. 

2) in the heading mode, there is now a 10 degree error to the right.  If the desired heading is 180, need to set the bug on 170.   The 10 degree offset is consistent all the way around the compass.  Seems to hold heading well , just 10 degrees off of what the bug indicates.

3) in the heading/GPSS mode,  no problem. The desired track and actual track are within 1 degree.

4) altitude holds OK as normal 

Where is the problem?

1) autopilot 

2) Aspen

3) not enough information to tell

I am thinking it is something in the output of the CDI and heading bug from the Aspen. From what I understand the Aspen GPSS is in a separate modular which performs the digital to analog conversion from GPS and feeds it direct to AP.   Not 100% on this.

Any other suggestions how to pinpoint the problem area?

Bill

 

 

 

[Cruiser]

need some clarification.

By CDI you mean the HSI display on the Aspen?

[wpbarnar]

Yes,  the Lateral indicator within the Aspen HSi

 

[Marauder]

I have a Stec 30, GTN 650, and Aspen with GPSS.   Although the airplane gets flown weekly,  the autopilot is not used as often.  This past weekend on a trip, I discovered the AP:
1) with AP in track mode {high or low) it will not track the CDI.  Doesn’t matter if the GPS or VOR is driving the CDI, the AP will not track.  Not even attempt or hunt, the airplane will circle to the right. 
2) in the heading mode, there is now a 10 degree error to the right.  If the desired heading is 180, need to set the bug on 170.   The 10 degree offset is consistent all the way around the compass.  Seems to hold heading well , just 10 degrees off of what the bug indicates.
3) in the heading/GPSS mode,  no problem. The desired track and actual track are within 1 degree.
4) altitude holds OK as normal 
Where is the problem?
1) autopilot 
2) Aspen
3) not enough information to tell
I am thinking it is something in the output of the CDI and heading bug from the Aspen. From what I understand the Aspen GPSS is in a separate modular which performs the digital to analog conversion from GPS and feeds it direct to AP.   Not 100% on this.
Any other suggestions how to pinpoint the problem area?
Bill
 
 
 

Bill - I am not too familiar with the STEC 30 on an Aspen. I have the STEC 60-2.

For scenario 1, if I want to fly the non-GPSS signal, I would put the unit in heading mode, (altitude hold if desired) then select Nav. This will have the autopilot fly like the old days of using just a CDI. What is puzzling for me is that it doesn’t sound like your unit is engaged. The Aspen is supposed to go into a wings level failure mode if the Nav signal is lost.

The 10° off thing is a calibration issue. I think it can be calibrated in the Aspen through one of the installer menus that avionics shops can get to.


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