Rain and autopilot unstable

[W9MV]

I have an S-tec 55 in a 1999 Piper Archer III.

Last weekend I was in moderate rain in a climb out of 2000 feet (900 AGL)
heading for 6000 feet when all of the sudden the nose pitched down.

I pushed the two drains located in the cockpit when the event first occured and
it did not solve the problem.

I disconnected the autopilot and handflew it. When it was safe to do so, I
engaged the autopilot again, and again, it would either pitch up or down.

Later in the flight when the rain had stopped, it worked as usual.

Any ideas?

Mark

[Nathan Young]

On 17 May 2004 22:09:08 GMT, (W9MV) wrote:

>I have an S-tec 55 in a 1999 Piper Archer III.
>
>Last weekend I was in moderate rain in a climb out of 2000 feet (900 AGL)
>heading for 6000 feet when all of the sudden the nose pitched down.
>
>I pushed the two drains located in the cockpit when the event first occured and
>it did not solve the problem.
>
>I disconnected the autopilot and handflew it. When it was safe to do so, I
>engaged the autopilot again, and again, it would either pitch up or down.
>
>Later in the flight when the rain had stopped, it worked as usual.
>
>Any ideas?
>
>Mark

Does it have a separate static line / static port than the
altimeter/VSI?

Wierd things can happen to the static equipment when in IMC/rain. The
altimeter in my Cherokee used to oscillate when in IMC. A new
altimeter and blow out of the lines fixed that problem.

-Nathan

[W9MV]

Thanks Nathan:

I did see the altimeter fluctuate during this event. I don't know if it does
have a seperate port, I don't think so but I will investigate.

The altimeter is only 3 years old, I'd hate to think it has already failed.

Thanks for your feedback, very helpful.

Mark

[Bill Hale]

(W9MV) wrote in message >...

The Stec is very sensitive to static port performance. On
some aircraft, like C 182 models, you need to add some
separate static ports to make it work.

I have a hunch that you have a little water in your static
system. If the changes in air pressure have to drive a water
plug, it will make the autopilot nuts.

Bill Hale BPPP instructor


> I have an S-tec 55 in a 1999 Piper Archer III.
>
> Last weekend I was in moderate rain in a climb out of 2000 feet (900 AGL)
> heading for 6000 feet when all of the sudden the nose pitched down.
>
> I pushed the two drains located in the cockpit when the event first occured and
> it did not solve the problem.
>
> I disconnected the autopilot and handflew it. When it was safe to do so, I
> engaged the autopilot again, and again, it would either pitch up or down.
>
> Later in the flight when the rain had stopped, it worked as usual.
>
> Any ideas?
>
> Mark