STEC 55X Alt VS and Trim Issue

[Txbyker]

I had a strange thing happen today while departing the busy Dallas Class B.  I have G-1000 with STEC 55X and at preflight I trim to takeoff position. Once I departed and began climbing to assigned altitude the autopilot trim, trimmed full down position when I activated the Alt and VS.  After fighting the yoke and trying to keep up with ATC telling me to climb at 1000 fpm I finally disengaged the trim rocker switch and used the manual trim wheel.  Each time I reactivated the trim rocker switch the plane pitched down and started full trim down from whatever position I had it at.  I hand flew altitude for half and hour and later own I switch the trim on again, without ALT engaged, and noticed I could trim the plane with the yoke trim switch.  I then reengaged ALT on the 55X and it held and did trim corrections as normal.  From that point on it all operated fine.

 

Any ideas what could have caused this?

 

Russ

[Danb]

Russ, good luck, I have a Bravo Gx with the same bastard system as you, the G1000 was made for the Garmin gfc auto pilot, I went through 3 computer boards for trims problems of all types, changed the trim servos twice and have put in a breaker between the computer and trim.. After having all the servos rebuilt again since Garmin would not work on the computer board until I did this...I have been ok for the last 100 hours. My plane went into a couple 360's in hard ifr ..anyway I do not believe our planes built with g1000 and stec 55x will ever be right...an engineer who was at mooney told me the only way We would be in the clear was to spend 60-70k to have the Garmin autopilot installed. We have been screwed and Mooney will do nothing. If we had enough pilots to do a class action against a Mooney?? I really hope all will be ok for you..there are some threads awhile back re this matter. Good luck. And keep eyes on panel you'll never know when your bird will fly crazily on its own....Dan

[John Pleisse]

I have a 55X with an Aspen 2000 system. May I suggest you look at the Altitude Can before getting into the G1000. Sometimes it can not work,  deflect full elevator before trim, then trim excessively to make up for it. I am utterly floored by your problems. Discretely, you have two of the best FCS's in GA. In unison, they are a train wreck.

 

John

[ghovey]

I had the same thing happen on an approach in IMC, barely able to hold the yoke back until I flipped off the electric trim Replaced all trim servos and it did it again and replaced the garmin board. 10k later finally got the problem fixed. It was not the servos

[flyboy0681]

Glad you recognized the situation as it was unfolding. As I wrote here a year ago, I experienced runaway down trim shortly after takeoff and for the second time in 33 years of flying, got an adrenaline rush that I was in a serious situation (the first time was when I lost power on x-wind). I found myself pulling back on the yoke with both of my elbows clutched behind the wheel. I finally looked down and saw the trim indicator in the full-down position, grabbed the trim and turned it like there was no tomorrow.

 

After a few more similar incidents (I was on my guard for those), it turned out to be the trim switch was sticking in the down position. 

[fastmooney2]

 The stec 55 never integrated well with the G1000. I  have heard that from a few other Mooney owners. Scared the bejeezes out of me one time climbing out in low ceilings it just pitched up hard as i went through 1000' altitude. Took me by surprise. Now i have another issue in that it wont hold a level altitude. All other functions work , tracking, heading etc. but when i set it to climb it will initially level off, then after 5-10 seconds, either starts to descend or climb. Stec said it might be the transducer...any thoughts?

[carusoam]

Welcome aboard FM

Best regards,

-a-

[fastmooney2]

Thanks!