I was wondering about something that happened when I flew with a KFC225 the other day.
We were doing the RNAV 23 into Bordeaux (LFBD). There were howling gales at altitude – we had 44 knots mostly as crosswind. And we were being followed by a 737 and had been asked to keep our speed up. I was flying it as a coupled approach to be sure I knew how the autopilot worked.
I did as asked and kept the speed up, around 130 KIAS, while in APR mode. Suddenly the aircraft rolled left and the AP disconnected (well, in the other order, but that was how it seemed to me).
No big deal, I picked it up and hand-flew the approach until ATC asked us to break it off so the 737 could get by.
The instructor I was with said it was because I was going too fast for the AP. I haven’t found any mention of this in the KFC225 manual.
Any thoughts on this (from Peter or any other KFC225 users)?
Suddenly the aircraft rolled left and the AP disconnected
That is by design. It happens at something like 45 deg roll or 20deg pitch.
The instructor I was with said it was because I was going too fast for the AP
The aircraft is not aware of wind; it flies relative to still air (disregarding secondary factors like wind shear versus aircraft inertia).
The KFC225 has no airspeed input so it is not aware either.
I hope the instructor is not charging too much 
The disconnect was due to turbulence exceeding the max roll angle – unless the autopilot is defective and just failed and that produced the roll. Was there really enough turbulence at your height to produce such a roll angle? LFBD is fairly flat, IIRC.
Wake turbulence?
Yes; possible.
If the autopilot reconnected OK later then the reason for the disconnection would have been just turbulence.
The disconnect was due to turbulence exceeding the max roll angle
That makes more sense. I doubt if it was wake turbulence because we were a way behind the previous traffic. But SOMETHING caused a sudden 20-30 degree roll, for sure. It was VERY windy although not especially turbulent.
As far as I can tell disconnects in APR mode are definitive. It will never pick up the glide slope again since it can’t intercept it. Although we weren’t yet on the glide slope so maybe I could have just reselected APR.
