STEC55X off track issue

I have a recurring issue with my STEC55X autopilot. The airplane remains right of course about 2 degrees (1/4 scale). It’s especially noticeable during coupled approaches using either the GPS (GNS430W) or Localizer. I have done inflight A/P calibrations on the PFD and manual alignments with a technician using a special screwdriver without success. It’s most noticeable during an ILS approach. The AP tries to center but then drifts right of course. I have replaced the PFD, based on apparently low voltages noted by my avionics shop, but the the problem persists.

If anyone has had a similar issue with the STEC55X please let me know if you resolved the problem. Attached is a picture of my PFD while enroute. Notice the airplane to the right of course on the CDI. Thank you for your help.6557.IMG_1287.jpg

Maybe, perform the roll trim in-flight test and check the trim motor start-up voltage.

I had that exact issue but only in GPSS mode. NAV was fine. Ended up sending STEC for service and that fixed the issue. There are certain calibrations that only STEC can do, would have to dig out an email from them about it.

Very simple fix. the are 2 small holes on the face of the 55x. One is for removing the unit from the tray, and the other hole is an aligning the track. You can turn the small adjustment left or right to get the autopilot back in alignment, or on the course line.

If you consult the STEC 55X install manual, It describes the procedure.


A couple of tips for the adjustment - it has to be done in flight, it’s quite sensitive, and you need a long fine point screwdriver. I made a tool from some piano wire with the end ground to a screwdriver tip.

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After rereading your original message it looks like you may have done that already. Maybe it’s time for a DFC90.

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I started a string on this a few months ago, same problem. That string has all the references to which screwdriver to buy, and how to adjust. It worked perfectly. I’m running now and can’t find the string and link to it, but if you search my posts you’ll find it. Feel free to PM me and I can call you later and talk you through it. Easy fix.

Here is the link. It is on the pay side though.

Thank you. I used the small screw driver you recommended and it helped. Needle not as far to the left as before. But I noticed it required quite a bit of turning for very small result. Was this your experience?

I was taking a check ride in my SR22 so I was concerned if it was off too much the examiner might make issue of the faulty autopilot. But all went well and now I can take my time addressing this issue.

Are you referring to the AP calibration that is done in flight? I’m not familiar with the roll trim inflight test.

I got a special screw driver but turning it gave me only a little improvement. Where you in NAV mode (not GPSS) when you made the adjustment? Also, when you turned the screwdriver did it roll immediately? Thanks.

A quick way to determine if your aircrafts flight controls and aileron trim tab are properly aligned is to do the in flight roll rate balance check. Fly to a safe altitude in smooth air With equal fuel levels. Trim the aircraft as best as possible for hands off flight. Run the Roll Trim full RIGHT while holding the aircraft level. Then bank to 30 degrees LEFT bank and release the controls. With a stopwatch, start timing as the attitude indicator passes through 20 degrees and stop timing as the attitude indicator passes through 0 degrees. Record that time. Now run the trim full LEFT, bank the aircraft to 30 degrees RIGHT bank and release the controls. With a stopwatch, start timing as the attitude indicator passes through 20 degrees and stop timing as the attitude indicator passes through 0 degrees. Record that time. Retrim the aircraft for straight and level flight. If the two recorded times are within .5 seconds of each other your aileron trim tab is properly set. If the recorded time difference exceeds .5 seconds then have your flight controls and trim tabs checked by a Cirrus Authorized Factory Service Center for proper rigging and tab alignment.

also, you may have a lazy turn coordinator!

I can’t recall if it was HDG or GPSS mode. Not NAV.