STEC-50 Heading Hold Failure - Need Advice

[DualRatedFlyer]

Took a nice trip from Lancaster PA to Hickory NC this weekend to visit some family.   I have been trying to duplicate a problem that I only see on long cross countries with my STEC 50.

Usually after departing IFR from LNS I get a few vectors that I use my heading mode on the autopilot for.  After a few turns I usually get direct to some way-point in the SFRA and continue on my assigned route through the SFRA.  

It seems like after around 1 hour of flying, my heading bug stops working.  I say 1 hour, because once I start my route I am usually on Nav mode and its not readily apparent when heading mode stops working, until I switch back to it if I am given vector/heading to fly. 

I have turned the autopilot off and then back on with no change.  I have pulled the circuit breaker and reset the unit with no joy. 

Sometimes at the end of my flight near my destination I will give it one more try, and it starts working again - sometimes it doesnt. 

It always works during the beginning of a flight. 

Not that it provides a lot of diagnostic help, but heres a short video of the issue after around an hour to an hour and a half of flying.  

https://photos.app.goo.gl/QAAWf96pTwGHegAw5

Any suggestions?

 

[Marauder]

45 minutes ago, DualRatedFlyer said:

Took a nice trip from Lancaster PA to Hickory NC this weekend to visit some family.   I have been trying to duplicate a problem that I only see on long cross countries with my STEC 50.

Usually after departing IFR from LNS I get a few vectors that I use my heading mode on the autopilot for.  After a few turns I usually get direct to some way-point in the SFRA and continue on my assigned route through the SFRA.  

It seems like after around 1 hour of flying, my heading bug stops working.  I say 1 hour, because once I start my route I am usually on Nav mode and its not readily apparent when heading mode stops working, until I switch back to it if I am given vector/heading to fly. 

I have turned the autopilot off and then back on with no change.  I have pulled the circuit breaker and reset the unit with no joy. 

Sometimes at the end of my flight near my destination I will give it one more try, and it starts working again - sometimes it doesnt. 

It always works during the beginning of a flight. 

Not that it provides a lot of diagnostic help, but heres a short video of the issue after around an hour to an hour and a half of flying.  

https://photos.app.goo.gl/QAAWf96pTwGHegAw5

Any suggestions?

 

It has been a while since I had a mechanical DG with HDG bug on my STEC. It seems like it was trying to turn but at a very slow rate. Have you done the full STEC AP checkout procedure from the manual? I agree for it to fail after flying a bit is unusual. Have you seen what it does if you completely disconnect the AP in flight and just try to put it back in HDG mode without switching from Nav?

Based on what I am seeing it could be a number of components. The DG heading bug could be problematic, the roll computer might be involved or the control head is not really going into HDG mode. Who are using for a shop? I would recommend using Smart Avionics at N71. He is extremely busy but is a fair guy and a good troubleshooter. 

[DualRatedFlyer]

7 minutes ago, Marauder said:

It has been a while since I had a mechanical DG with HDG bug on my STEC. It seems like it was trying to turn but at a very slow rate. Have you done the full STEC AP checkout procedure from the manual? I agree for it to fail after flying a bit is unusual. Have you seen what it does if you completely disconnect the AP in flight and just try to put it back in HDG mode without switching from Nav?

Based on what I am seeing it could be a number of components. The DG heading bug could be problematic, the roll computer might be involved or the control head is not really going into HDG mode. Who are using for a shop? I would recommend using Smart Avionics at N71. He is extremely busy but is a fair guy and a good troubleshooter. 

It does seem to want to turn... but just cant commit.  I have done the full checkout listed in the "STECT 50 Functional Preflight Procedures" http://aerofliers.org/documents/s-tec-40-50-operating-manua.pdf  I believe this is what you are referring to. 

I **think** I have done a full disconnect and went straight to HDG mode without switching from NAV.  I will check this box for sure next time I fly.  Even when HDG mode stops working, the Turn Knob continues to function normally - so I end up commanding a turn until reaching a desired heading and then moving the Turn Knob back to neutral to remain on that heading.  

So far the only avionics work I have had done was at Lancaster Avionics with my IFD 440 install.  We are both based on the same field.  Thought I would shop around the issue a bit on here to see if anyone had any ideas before contacting a shop.