How does one have CATIA calculate the area (not mass) moments of inertia for a surface (of section cut) in V5 ? It was done by default in V4 for a FACE in the analysis function.
Create a plane where you want the moments of inertia for your section cut. Go in the sketcher mode use the "intersect 3D elements" icons select your body (you'll have the complete boundary of your part). Switch to surface then simply fill this boundary (Fill function). After do an inertia analysis of this new surface.