Rolling aircraft when rotating towards an object

Hello everybody,

I'm trying to rotate aircraft through an object. Lets think about a target cube. My aircraft going to it with its forward vector.

 this.transform.position += this.transform.forward * dt; 
 Quaternion lookTo = Quaternion.LookRotation(targetDirectionP);    
 this.transform.rotation = Quaternion.Slerp(this.transform.rotation, lookTo, dt); //Quaternion.RotateTowards

As a natural aircraft movement, I'm trying to roll aircraft around its forward vector by DT while turning but its forward vectors y value changes quickly. How can I handle this problem? I've tried every combination of Quaternion class' rotate functions but none of them works.

When I try to make Quaternion multiplication like below;

 this.transform.rotation = Quaternion.Euler(this.transform.eulerAngles.x, this.transform.eulerAngles.y, dt) * this.transform.rotation;

it is turning crazy and forward vectors Y value is still changing.