Originally Posted by
Owain Glyndwr
PS: Looking at the traces again with a critical eye I see there was a permanent small rudder trim offset ( 0.5 deg right rudder) which could have generated a slow spiral divergence to the right.
Right, but the rudder position appears to be more-or-less centred correctly. Would the Yaw Damper not compensate? Unfortunately the graphs are imported at a low resolution, so it's harder to determine exactly what the Yaw Damper and TLU were doing exactly (0.5 degrees offset being relatively minor on those graphs).