@ivan.k.m.ho I thought you were after something like this.
Cylinder and a curve.
Project the curve onto the cylinder
Subdivide the faces around the projected curve
Delete the faces inside the curve
I selected the points around that edge and used tsPull to get them onto the projected curve. I have some distortion in the cylinder because I did not subdivide enough. Will fix that in a minute.
Select the edge and extrude.
I used tsPull to get the points of the extrusion to match the initial planar curve. I also added an edge loop to the left and right sides to get rid of some distortion in the cylinder.
To tidy up that top section select all the faces.
Change the edit mode to vertices/points with those faces selected.
Run tsFlattenPoints to straighten it up.
This is the finished result. Much easier to just do it Nurbs IMO. I would only do it like this if I really had to have a t-Spline object. HTH.