Hi, we have been flying the Bergen Intrepid Gas EB. For maintaining the heading, Futaba GY611 Gyro and controller have been mounted, along with S9256 servo. We did not face any heading problem in flight until now. During the recent couple of flights, the helicopter started yawing all of a sudden or in case of a disturbance. In some cases, it was able to return to its original heading, but only after turning for about 90 degrees. In other cases, it was unable to return to the original heading and it continued yawing while executing one or two complete rotations (in the direction opposite to that of the main rotor rotation). We tried replacing all the corresponding components like gyro, controller and servo but the problem still persists. The gain values have always been the same. The helicopter is always flown in AVCS mode. The following values are the current gains being used.

GY611 Gyro Gain Settings:
DIR = REV
G:1A = 35%
G:2N = 100%
NCG = A 130%,B 130%
ACG = A 120%,B 70%
D1I = A 0%, B 0%
D1D = A 0%, B 0%
TRK = 0%
MODE = CMT
FMOD = F3C
AVS =100%
LMT = A 100%, B 100%

What could possibly be the problem? Could the gain settings be incorrect?