Autopilot Trim-Fail Warning over the Ötztal-Alps
On February, 20th 2015 on a sightseeing flight with two passengers on board the Diamond DA40 (D-ERRP) we encountered a Trim-Fail Message of the autopilot system (KAP140 2-axis-autopilot) at about 12500ft above MSL ...
On that day we departed LOWI at about 15:40 UTC from runway 08. Thereafter we flew through the Selltaintal to Kühtai and turned into the Ötztal. In the Terminal Area Forecast (TAF) valid for LOWI at that time a moderate (~ 30-40kt) southern flow was forecasted in the west and southern parts of Austria. After reaching the area of Sölden I could see the flow from about 180-200° at 40kt on my Primary Flight Display (PFD) but the flow was indeed very steady and smooth. So I continued flying the aircraft on the autopilot. From time to time the autopilot system announced "Trim in motion" which is absolutely normal and indicates that the trim was active (induced by the autopilot to hold the assigned heading and altitude) at time of call out for at least 5 seconds. Near Wildspitze a Trim Fail Warning message appeared at the ECU-Display which indicates that the autopilot trim system failed (the picture shows all messaged flashing during the preflight check).
As proposed in the Pilot Operating Handbook (POH) I disconnected the autopilot and got manual control on the aircraft. Thereafter I acknowledged the Warning-Message on the ECU-Display and took the autopilot down from the aircrafts electrical system (e.g. I pulled the associated circuit breaker). The manual trim of the aircraft is still possible only the autopilot with its trim function and the electrical trim was disconnected from the system. So I continued manually flying the aircraft back to Innsbruck. In the end the passengers did not even recognize the malfunction in the system.
After this report that incident might appear to you as this was near an emergency but in fact it was not. Such a malfunction of the autopilot is well described in the POH and there it is not declared as an emergency. With such a failure, sure, you are going to fly back to your airport and report it to the aircraft holder.
If you are interested in the KAP140 2-axis-autopilot system check out the following PDF-document ... (KAP140 BENDIX/KING autopilot system.pdf)