Question about velocity

Hello,
I’m trying to experiment with the movement component of the character and the speed, I’m trying to adjust the speed from walking to falling and then hitting the flight button (boolean).
My problem is when I’m in flight mode, because pressing the input “forward” the Z velocity suddenly changes from around 200 to 50 units. I attach a picture.
I want the forward input not to change the Z speed while the button is pressed, because I would like to drive it independently.
i’ve tested by split and not connect the Z float but no change.
(no physic is used only simulating)