Abstract: Process for manufacturing a monolithic fan cowl (9) of curvilinear shape for aircraft engines comprising the following steps: a) providing a skin (1) cured, several longitudinal hat frames (3) uncured and several transversal hat frames (5) cured; b) placing said longitudinal hat frames (3) on the skin (1) c) placing said transversal hat frames (5) over the longitudinal frames (3) and the skin (1); d) covering the assembly with a vacuum bag; e) performing an autoclave cycle under high temperature and pressure conditions for co-bonding the skin (1) and the longitudinal hat frames (3), and for a secondary bonding of the transversal hat frames (5) to the skin (1) and the longitudinal hat frames (3).