A/P disengagement

Dear Fellow Cirrusites:

N1952K has been our newest family member since February 15 of this year and the love affair is steamier than ever. After 40 hours I still find the aircraft totally amazing and I am clearly spoiled by all the goodies what our spam-can driver brethren can only drool after.
Today, however a very odd thing happened when we were coming home into the ChicagoLand area. The lake shore was busier than ever with a full compliment of sightseer GA aircrafts coupled with the usual commercial traffic headed to O’Hare. I just cancelled IFR heading North along the lake shore but still in contact with Chicago center with the autopilot in the HDG mode. Skywatch was doing a great job and I knew where every flying contraption was around us.

At one point however, when I got the annoying “traffic, traffic” warning the A/P suddenly disengaged and the 22 started a gentle climbing turn. The following couple of second were mighty interesting saying the least. There were at least 15 - 20 aircrafts of all kinds around us (pretty common around ORD) and I knew that at least one was very close while I had my aircraft making a climbing turn on its own.
Well, it took only a couple of seconds to reestablish order but, it sure seemed like an eternity.
In retrospect, neither my passenger nor I recalled any conscious act of disengaging the A/P. We were both very busy watching for traffic especially when the traffic alert was announced. The possibility that in the excitement one of us could have pushed the A/P disengage button certainly exists but, neither of us recalled that. Also, the aircraft was not making any abrupt maneuvers that could have caused the A/P to disengage. The POH did not offer any help in explaining what happened.

Does anybody have any thoughts?

Appreciate your input.

I’d bet that one of you did accidentally hit the disconnect button. I’ve done it several times with a hand, or once while opening a Jepp book and having the cover hit the switch. My wife has also on occasion managed inadvertently to disconnect the thing without realizing it. That’s why they have the loud autopilot disconnect warning signal.

On our 22 the turn cord went bad. We would be going along and after sometimes a hour it would disconnect. The turn cord worked fine but did not have enough spin to make the a/p computer happy. Good luck…Ed

I see from the registration that you’ve got an SR22. There are a couple of things to consider. First, the a/p in the SR22 will disengage if you even touch the pitch trim (you don’t need to depress the button, just bumping it up or down will do the trick.) Secondly, the SR22 has a separate pitch servo for the autopilot that is separate from the pitch trim. As such, it only runs the pitch trim when the control forces on the servo are beyond a certain level, so it is quite normal for there to be some residual pitch trim in one direction or the other when the autopilot is disconnected, particularly if the autopilot is working a bit to hold altitude.

For that matter, it is typical to have at least some residual roll left when the autopilot disconnects, as you’re left with aileron trim in whatever instantaneous position it was in when it disconnected.

My guess is that you probably just brushed the trim hat, and all this is normal.

One of our autopilots (we’re on our 5th) had this problem only more severe. It would disconnect, and you could not re-engage it for a period of time. The actual “power” to it was not there. There was no green light in which to re-engage. After a while (the timeframe varied, but in the beginning it was within several minutes) you could turn it back on.

In our aircraft the airplane is never in perfect trim. The autopilot oscillates the ailerons a bit back and forth and depending upon the air will sometimes be out of pitch. You don’t notice this when flying on the autopilot, but will notice it when you disengage.

The solution to the disconnecting was naturally, another new autopilot!


That explains the A/P disconnect but what about the uncommanded climbing turn? It should have been trimmed for straight and level by the A/P. He must have the newer Skywatch which not only warns you of nearby traffic but guides you away from it:)

That explains the A/P disconnect but what about the uncommanded climbing turn?

When I disconnect my autopilot, unless I apply constant pressure to the yoke the plane will fly enter a turn either ascending or descending. It does not have a neutral trim position.

Please see Dave Katz’s reply above for your answer. It is easy to accidentally disconnect the AP and the airplane may well not be in perfect trim.


Your post suggests that the SR22 AP has trim-followup. I.e., a system whereby the AP will trim the airplane in both pitch and roll. I had thought that while of course the roll is done through the roll trim, that the pitch was done with a separate servo, with no trim followup. In my SR22, the AP will flash the trim-up or trim-down indicators when the servo is at its limit and needs me to manually trim it. But if you are right, then there is something wrong with my AP in pitch.

As I read the 55X supplement in the SR22 POH you shouldn’t have to ever manually trim when on autopilot. It is a little confusing because on p.2 of the supplement they list all of the things that are not implemented in the SR22 and then you have to read the S-Tec manual and try to figure out what the differences are. The SR22 POH says that the “optional trim servo” is not implemented. The S-Tec manual on p.23 refers to the “pitch servo”. I think they are talking about the same thing. On p.24 the S-tec manual says that the up or down trim symbol will illuminate indicating trim in motion and the direction of travel. I have never paid attention to this but next time I fly I will put some hand pressure on the stick and see if the trim symbol illuminates when it tries to trim against the pressure. As a complaint for Cirrus - I think the combination of the POH supplement and the S-Tec manual stinks, especially when they don’t always use the same terms. The supplement should rewrite the S-Tec manual so we can see what really applies to the SR22.

The SR22 is wired for “autotrim”–it will run the trim to reduce forces on the pitch servo (the annunciator should come on for a bit and then go off.) If you have to manually trim in pitch (presumably disconnecting the autopilot and then enabling it again when you’re done) then something is definitely goofy.

Jim, not only should you not have to trim when using the autopilot, my autopilot (and I suspect all others in SR22s at least) will disconnect if you manually trim while the A/P in on.
Be careful if you apply manual force to the controls while on autopilot. It should trim against the force and will eventually disconnect leaving you in a significantly out of trim condition.

Thanks for the clarifications. I suspect that the problem was with my understanding. I’ll do some experiments to confirm what you’ve told me works correctly in my a/c.

I agree with the other poster who said the collection of manuals and supplements on this topic are confusing.