Auto Pilot stopped tracking

Dean

Dean

Pattern Altitude
Joined
Mar 11, 2005
Messages
2,222
Location
Southwest Missouri
Display Name
Display name:
Dean
On the way back from Tulsa Friday the autopilot(STEC-40) stopped tracking the heading bug and the nav. No sign what so ever that it was going on the blink. I can turn the wing leveler knob and nothing happens. Anyone know if this is a known problem of the STEC? Or if any of you have had the same problem.
 
Dean said:
On the way back from Tulsa Friday the autopilot(STEC-40) stopped tracking the heading bug and the nav. No sign what so ever that it was going on the blink. I can turn the wing leveler knob and nothing happens. Anyone know if this is a known problem of the STEC? Or if any of you have had the same problem.
Click to expand...

If the turn knob has no effect in wing leveler mode the problem is either the computer, the servo, or the wiring. My money would be on the servo. A factory authorized shop can isolate the problem pretty quickly if access isn't too tough. The only thing you can easily check is for connectors come loose, but IIRC that's not likely on an STec.
 
lancefisher said:
If the turn knob has no effect in wing leveler mode the problem is either the computer, the servo, or the wiring. My money would be on the servo. A factory authorized shop can isolate the problem pretty quickly if access isn't too tough. The only thing you can easily check is for connectors come loose, but IIRC that's not likely on an STec.
Click to expand...
IIRC the STec has a computer, a servo and takes it's signal from the turn coordinator. Any of the three could be the problem.

I agree, take it to an authorized shop to get each component checked.
 
I had the motor burn out on the STEC autopilot.
 
Does the autopilot still work as a wing leveler? If so, the servo is not the problem, as it must function to maintain wings level.

Assuming that (which I am, as I think you would have just written that the autopilot stopped working entirely otherwise), since it affects both tracking and roll with the manual roll knob, I expect the problem is in the controller itself.
 
lancefisher said:
If the turn knob has no effect in wing leveler mode the problem is either the computer, the servo, or the wiring. My money would be on the servo. A factory authorized shop can isolate the problem pretty quickly if access isn't too tough. The only thing you can easily check is for connectors come loose, but IIRC that's not likely on an STec.
Click to expand...

I called a local STEC shop this morning and the tech is leaning toward the servo, then the computer. I hope its the servo, much cheaper to fix.:yes:
 
My sympathies. I had a similar problem this past summer and it turned out to be a broken wire from the heading bug to the AP, but it took a while to find as the DG had also gone TU and needed to be rebuilt. So for a while we were chasing a problem internal to the DG, then when we finally were able to rule that out it got sorted out, but it took over a month,
 
I had the altitude hold servo go out a couple of years ago. The shop said it was "toast" internally....

If the computer (e.g. the panel lights) all seem OK, I'd look at the servo.
 
Are flight control servos in a full-size plane a stepping motor like those in models? If so, how fine are their movements? Meaning, how many degrees of turn in a step?
 
Servos are not steppers; typically, they are analog controlled by a feedback loop such that the null position is moved electronically based upon demand for control movement.
 
I've never had my ULNA autopilot fail. I would look into installing one of these.
 
You must log in or register to reply here.
Back
Top