View Full Version : Unusual Behaviour

08-12-2013, 10:57 PM
On Sunday I was flying along with the AP engaged following the heading and altitude bugs on the 4500. Everything was fine until ATC announced a pressure change from 1016 to 1017 mlb. When I made the adjustment on the Baro...the aircraft suddenly began to ascend, in a pitching or jerking motion...almost like a stepping function. It was reasonably violent, like someone jerking back the stick, releasing, jerking back, etc. We rapidly gained 500 feet in the span of 30 seconds until I disengaged the AP.

I descended, made sure everything appeared okay and re-engaged the AP. Again it followed the 4500 bugs. I then changed the Baro back to 1016 and it exhibited the same behaviour.

Later in the flight I engaged the AP and changed the Baro and everything seemed ok?

Rob Hickman
08-13-2013, 01:08 PM
Sounds like the AP pitch servo was slipping. Do you have auto trim? If the elevator is not in trim it could be near the torque limit and a small altitude change would cause it to slip.

08-13-2013, 01:26 PM
Thanks...that's what I suspected but I do have auto trim.

08-15-2013, 11:53 AM
You may need to speed the autotrim up a little bit.