S-TEC 60-2 Altitude Hold Problem

[Peter Rejto]

A new problem surfaced yesterday with my S-TEC 60-2 which has been super reliable for many years. I'm sure I will need to take this to a shop but I'm curious if anyone might guess what is going on?

Tracking works as expected. Vertical hold seems to work fine for a few minutes but then commands a very sudden and rapid pitch down (and less frequently a sudden pitch up). Today I flew again and these failures did not happen but altitude hold was accompanied by a lot of porpoising. 

Thanks,

Peter

[vorlon1]

Had the same behavior with mine. Turns out the wiring to the pressure transducer was faulty. Check that as well as the transducer itself.

[carusoam]

Find the pressure transducer, and see how good the hose to the static system is...

Often, a low cost rubber hose is used to connect to the static system...

Old hoses leak... the AP senses the slight vac of the cabin instead...

Next thing you know... the AP thinks you are at a higher altitude and starts to adjust for it...

PP thoughts only, not a mechanic...

Best regards,

-a- 

[thinwing]

had the same problem on a baron...replacement pressure transducer located behind the panel and connected to static line (blue plastic top with nipple)cured the problem

[Peter Rejto]

Thanks for all the replies. The tubing to the pressure transducer was quite brittle with numerous small cracks...but, I don't think it was actually leaking. In any case the tubes are now replaced and I've exercised the pitch servo.

I'm flying today and will report any results.

Peter

[DXB]

19 minutes ago, Peter Rejto said:

Thanks for all the replies. The tubing to the pressure transducer was quite brittle with numerous small cracks...but, I don't think it was actually leaking. In any case the tubes are now replaced and I've exercised the pitch servo.

I'm flying today and will report any results.

Peter

FWIW the STEC-30 and STEC-60 altitude hold systems are very similar I believe - there are numerous possibilities I tried to document in this tread, including excercising servos - which didn't work for me. My problem got worse and worse until it liked to behave like an prototype for the 737 MAX MCAS system 

Amazingly, painting some liquid semiconductor (Stabilant 22)  on the contacts for the connector between the pressure transducer and the panel unit completely solved the problem, and it has worked perfectly since.  I certainly wouldn't pay anyone to look at it until you've tried that....

 

[Peter Rejto]

I seem to have fixed the problem. Flew 1.4 hours today and altitude hold was perfect. I’m not sure if it was the hoses or running the servo but hopefully things remain fixed. 

Thanks again for all the suggestions!

Peter

[carusoam]

Nice follow up Peter!

Thanks for sharing it...

Best regards,

-a-