STEC-30 GPSS Tracking-67 M20F

[Bryan G]

Hello everyone,

My STEC-30 with alt hold and GPSS has always worked great, but it never keeps my Mooney perfectly on track. It doesn’t wander, it just holds a slight offset. Flies perfectly straight from A to B, just ever so slightly off. As soon as I engage GPSS, it flies to this deviation from on course to slightly off. Any ideas?

Thanks,

Bryan

 

 

[Ragsf15e]

2 minutes ago, Bryan G said:

Hello everyone,

My STEC-30 with alt hold and GPSS has always worked great, but it never keeps my Mooney perfectly on track. It doesn’t wander, it just holds a slight offset. Flies perfectly straight from A to B, just ever so slightly off. As soon as I engage GPSS, it flies to this deviation from on course to slightly off. Any ideas?

Thanks,

Bryan

 

 

I have the same set up and mine does that as well. A little less than yours, but very similar. There is an adjustment on the stec, to correct that, but mine is so close that I decided not to touch anything and possibly mess up something else. I think it is a screw to turn in a relatively simple adjustment, but you’ll have to look through the maintenance manual or other installation manual.

[Ragsf15e]

I want to say there’s a screw below/behind the lower left (or maybe right?) mounting screw that is an adjustment.

[Bryan G]

Thanks @Ragsf15e that was quick, I’ll give it a look later this week!

[Ron McBride]

My gns 430 can adjust the track slightly offset, could your navigator be doing that.   You will need to read the owners manual.  
 

[Ragsf15e]

1 hour ago, Ron McBride said:

My gns 430 can adjust the track slightly offset, could your navigator be doing that.   You will need to read the owners manual.  
 

Interesting, I haven’t heard that, do you know where that setting is?

My stec is slightly off center regardless of mode though- gps, vnav or even heading.

[Ragsf15e]

1 hour ago, Bryan G said:

Thanks @Ragsf15e that was quick, I’ll give it a look later this week!

Again, I haven’t tried it but I found a little more info from Btalk.  It’s called the trim pot.  Upper left screw.  Question was, can I adjust it myself?

”Legally? No. But for the STec 30 you remove the upper left screw on the turn coordinator that is the autopilot. Then you stick a very small diameter screw driver into that hole and turn the pot in the direction you want to correct for, in my case counterclockwise. You turn it a little and then give it a minute or so to correct. Repeat as necessary. Don't know how the 55X works.”

[DXB]

3 hours ago, Bryan G said:

Hello everyone,

My STEC-30 with alt hold and GPSS has always worked great, but it never keeps my Mooney perfectly on track. It doesn’t wander, it just holds a slight offset. Flies perfectly straight from A to B, just ever so slightly off. As soon as I engage GPSS, it flies to this deviation from on course to slightly off. Any ideas?

Thanks,

Bryan

 

 

Take out bottom right screw holding control head to the panel.  Get a very fine long skinny flat screw driver (~1mm).  I carry in my flight bag to recalibrate periodically. When in GPSS mode in flight in smooth air, display crosstrack error on your navigator.  Insert screwdriver gently to base of screw receptacle and make small turns toward the course until it settles out.  I can get it within 0.02nm.

[Ragsf15e]

Ha!  So it’s one of the screws… @DXB is probably right.  Sounds like he’s done it before.

[Bob Weber]

The following is an excerpt from a Sys 30 manual, the adjustment is in deed in the lower RH bezel screw.

I like the use of GPSS and watching the track line for centering.

 

4.7 Roll Centering Adjustment
The Roll Centering Adjustment
compensates for any offset that may exist
in the Turn Rate Signal, which
is internally processed by the
Turn Coordinator / Roll Computer. This
adjustment should be performed on the
ground, following replacement of the
Turn Coordinator / Roll Computer. It
should also be performed in flight, if one
of the following symptoms is observed:
1. Heading Bug is offset from the Lubber
Line, while holding a heading with the
heading mode engaged.
2. CDI needle is offset from center, while
tracking a course with a navigation mode
engaged (LO TRK, HI TRK).
4.7.1 Aircraft on Ground Adjustment
4.7.1.1 Preparation for Adjustment
a. Set Autopilot Master Switch to OFF
position.
b. Set Avionics Master Switch to OFF
position.
c. Set Battery Master Switch to OFF
position.
d. Set APU Power Switch to OFF
position.
e. Connect APU to A/C.
f. Set APU Power Switch to ON position.
g. Set Battery Master Switch to ON
position.
h. Set Avionics Master Switch to ON
position.
i. Set Autopilot Master Switch to ON
position.
j. Wait until RDY lamp alone becomes
illuminated on AP display.
k. Turn OFF Navigation Receiver to
center CDI needle.
l. Engage LO TRK mode.
4.7.1.2 Adjustment Procedure
a. Insert the Roll Centering Adjustment
Tool, PN 95101-1, into the bezel hole
shown in Fig. 4-2, until it makes contact
with the Roll Centering Potentiometer.
Caution: To prevent internal equipment
damage, do not apply excessive pressure
to the Roll Centering Potentiometer.
b. Adjust the Roll Centering
Potentiometer in small increments, until
A/C Control Wheel movement is nulled.
Note: Allow time between adjustments for
autopilot to stabilize.
4.7.2 Aircraft in Flight Adjustment
4.7.2.1 Preparation for Adjustment
a. Trim aircraft for level flight.
b. Intercept a course.
c. Engage LO TRK mode.
4.7.2.2 Adjustment Procedure
a. Insert the Roll Centering Adjustment
Tool, PN 95101-1, into the bezel hole
shown in Fig. 4-2, until it makes contact
with the Roll Centering Potentiometer.
Caution: To prevent internal equipment
damage, do not apply excessive pressure
to the Roll Centering Potentiometer.
b. Adjust the Roll Centering
Potentiometer in small increments, until
A/C Control Wheel movement is nulled.
Note: Allow time between adjustments for
autopilot to stabilize.

Edited August 9, 2023 by Bob Weber

[Ragsf15e]

3 hours ago, Bob Weber said:

The following is an excerpt from a Sys 30 manual, the adjustment is in deed in the lower RH bezel screw.

I like the use of GPSS and watching the track line for centering.

 

4.7 Roll Centering Adjustment
The Roll Centering Adjustment
compensates for any offset that may exist
in the Turn Rate Signal, which
is internally processed by the
Turn Coordinator / Roll Computer. This
adjustment should be performed on the
ground, following replacement of the
Turn Coordinator / Roll Computer. It
should also be performed in flight, if one
of the following symptoms is observed:
1. Heading Bug is offset from the Lubber
Line, while holding a heading with the
heading mode engaged.
2. CDI needle is offset from center, while
tracking a course with a navigation mode
engaged (LO TRK, HI TRK).
4.7.1 Aircraft on Ground Adjustment
4.7.1.1 Preparation for Adjustment
a. Set Autopilot Master Switch to OFF
position.
b. Set Avionics Master Switch to OFF
position.
c. Set Battery Master Switch to OFF
position.
d. Set APU Power Switch to OFF
position.
e. Connect APU to A/C.
f. Set APU Power Switch to ON position.
g. Set Battery Master Switch to ON
position.
h. Set Avionics Master Switch to ON
position.
i. Set Autopilot Master Switch to ON
position.
j. Wait until RDY lamp alone becomes
illuminated on AP display.
k. Turn OFF Navigation Receiver to
center CDI needle.
l. Engage LO TRK mode.
4.7.1.2 Adjustment Procedure
a. Insert the Roll Centering Adjustment
Tool, PN 95101-1, into the bezel hole
shown in Fig. 4-2, until it makes contact
with the Roll Centering Potentiometer.
Caution: To prevent internal equipment
damage, do not apply excessive pressure
to the Roll Centering Potentiometer.
b. Adjust the Roll Centering
Potentiometer in small increments, until
A/C Control Wheel movement is nulled.
Note: Allow time between adjustments for
autopilot to stabilize.
4.7.2 Aircraft in Flight Adjustment
4.7.2.1 Preparation for Adjustment
a. Trim aircraft for level flight.
b. Intercept a course.
c. Engage LO TRK mode.
4.7.2.2 Adjustment Procedure
a. Insert the Roll Centering Adjustment
Tool, PN 95101-1, into the bezel hole
shown in Fig. 4-2, until it makes contact
with the Roll Centering Potentiometer.
Caution: To prevent internal equipment
damage, do not apply excessive pressure
to the Roll Centering Potentiometer.
b. Adjust the Roll Centering
Potentiometer in small increments, until
A/C Control Wheel movement is nulled.
Note: Allow time between adjustments for
autopilot to stabilize.

Bob, that’s awesome, thanks so much for sharing your expertise!

[Bryan G]

Thanks for the help everyone, life has been a little busy but I was able to make the adjustment and it tracks great!
 

[Bob Weber]

On 8/9/2023 at 10:53 PM, Ragsf15e said:

Bob, that’s awesome, thanks so much for sharing your expertise!

https://webairconsulting.com/

You are welcome

I assist folks all over the planet troubleshooting the old systems I spent 40+ years installing and repairing.

Quite often my guidance can navigate you thru the diagnostics without swinging a prop!

My record time was 15 minutes, a guy with a Cessna 340A, flying in the soup routinely, in Queensland Australia with his family aboard.

We spoke for 5 minutes ground checking the system looking for a trim issue in his 400B IFCS system.

He hesitated after I had him turn on the Avionics Master, saying "it does this sometimes".

I could hear him flipping the switch several times before he said OK what's next?

When I asked him about what just happened, he said the radios won't come on without flipping the switch like I heard.

I answered his question by requesting he put an out of service tag on the aircraft and send me a picture of it.

in minutes I got the pics from 9,000 miles away.

Where's waldo?

He said it was doing this for years and getting worse...