Create cross section curves from stl file

I got an airplane cockpit in stl format whom I would like to trace cross section curves, using splines, along the airframes longitudinal axis. Using the loft function it should then be a simple task to create a solid surface of the cockpit.

I thought the cross section view would be possible to use but it doesn’t cut the stl file as expected possibly since its not a solid surface but rather a sheet body.

Any suggestion on how this process can be achieved?

Attached figure is showing two curves of what I would like to do… the red object is the imported stl file of the fuselage.

If only there was a capture sketch to a plane at intersection.

Can you slice the model at that point and use the cut face to sketch on?