Whats the reason for helicopters drifting after switching into auto- mode?
If helicopter drifts slowly only in one direction, it maybe result from moving of some strick accidentally when the user switches the helicopter into auto mode. This is always caused by some input of a stick when switching into the auto mode. If such situation occurs, there is an easy solution to handle this. What you need to do is only release all sticks and switch to manual mode and then switch into auto-mode quickly.