Rain and autopilot unstable

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

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

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

(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