Bank angle is the angle that a plane turns when it is making a turn. It is similar to when you want to make a turn on a swing at the park. When the swing is going in a straight line, your body is straight. But when you want to turn, you lean to one side. When a plane is making a turn, it does the same thing. The wings tilt to one side and the plane tips a certain way. That angle the plane tips is called the bank angle.